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The Eastern Bering Sea Shelf
m
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Bepimi Sea Shelf:
ani MesoMrce
Edited by Donald W. Hood and John A. Calder
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UNITED STATES
DEPARTMENT OF COMMERCE
Malcolm Baldrige, Secretary
UNITED STATES
DEPARTMENT OF THE INTERIOR
James E. Watt, Secretary
BUREAU OF LAND MANAGEMENT
Robert F. Burford, Director
NATIONAL OCEANIC AND
ATMOSPHERIC ADMINISTRATION
John V. Byrne, Administrator
OFFICE OF MARINE POLLUTION
ASSESSMENT
R. L. Swanson. Director
Published in 1981
by the Office of Marine Pollution Assessment
of the National Oceanic and Atmospheric Administration
with financial support from the United States Department of the Interior,
Bureau of Land Management
Library of Congress Catalog Card Number 81-600035
Distributed by the
University of Washington Press
Seattle, Washington 98105
Contents
Volume I Errata ix
VI: Marine Birds 627
Feeding Ecology of Seabirds of the Eastern Bering Sea
George L. Hunt, Jr., Barbara Burgeson, and Gerald A. Sanger 629
Breeding Distribution and Reproductive Biology of Marine Birds in the Eastern Bering Sea
George L. Hunt, Jr., Zoe Eppley, and William H. Drury 649
Pelagic Distribution of Marine Birds in the Eastern Bering Sea
George L. Hunt, Jr., Patrick J. Gould, Douglas J. Forsell, and Harold Peterson, Jr. 689
Shorebirds of the Eastern Bering Sea
Robert E. Gill, Jr. and Colleen M. Handel 719
Waterfowl and Their Habitats in the Eastern Bering Sea
James G. King and Christian P. Dau 739
VII: Interaction of Ice and Biota 755
Ice-Biota Interactions: An Overview
V. Alexander 757
Primary Production at the Eastern Bering Sea Ice Edge: The Physical and Biological Regimes
H. J. Niebauer, V. Alexander, and R. T. Cooney 763
The Role of Epontic Algal Communities in Bering Sea Ice
V. Alexander and T. Chapman 773
Ice as Marine Mammal Habitat in the Bering Sea
John J. Burns 781
Birds and the Ice-edge Ecosystem in the Bering Sea
George J. Diuoky 799
VIII: Mammals 805
Marine Mammals of the Eastern Bering Sea Shelf: An Overview
Francis H. Fay 807
Feeding and Trophic Relationships of Phocid Seals and Walruses in the Eastern Bering Sea
L. F. Lowry and K. J. Frost 813
Foods and Trophic Relationships of Cetaceans in the Bering Sea
K. J. Frost and L. F. Lowry 825
Distribution and Abundance of Sea Otters in the Eastern Bering Sea
Karl B. Schneider 837
Northern Fur Seals in the Bering Sea
George Y. Harry and James R. Hartley 847
The Energy Cost of Free Existence for Bering Sea Harbor and Spotted Seals
S. Ashwell-Erickson and R. Eisner 869
IX: Microbiology 901
Microbiology of the Eastern Bering Sea
Richard Y. Morita 903
Fish Diseases in the Bering Sea
B. B. McCain and W. D. Gronlund 919
X: Plankton Ecology 931
Phytoplankton Distribution on the Southeastern Bering Sea Shelf
J. J. Goering and R. L. luerson 933
Bering Sea Zooplankton and Micronekton Communities with Emphasis on Annual Production
R. Ted Cooney 947
Nutrient Distributions and Dynamics in the Eastern Bering Sea
Akihiko Hattori and John J. Goering 975
Distribution of Walleye Pollock Eggs in the Uppermost Layer of the Southeastern Bering Sea
Tsuneo Nishiyama and Tsutomu Haryu 993
XI: Fisheries Biology 1013
Commercial Use and Management of Demersal Fish
R. Bakkala, K. King, and W. Hirschberger 1015
Eastern Bering Sea Crab Fisheries
Roberts. Otto 1037
vi
XII: Benthic Biology 1067
Benthic Invertebrate Macrofauna of the Eastern Bering/Chukchi Continental Shelf
Sam Stoker 1069
A Survey of Benthic Infaunal Communities of the Southeastern Bering Sea Shelf
Karl Haf linger 1091
Disturbance and Diversity in a Boreal Marine Community: The Role of Intertidal Scouring by Sea Ice
Charles E.OVlair 1105
Epifaunal Invertebrates of the Continental Shelf of the Eastern Bering and Chukchi Seas
Stephen C. Jewett and Howard M. Feder 1131
Bivalve MoUusks of the Southeastern Bering Sea
J. McDonald, H. M. Feder, and M. Hoherg 1155
Stock Assessment and Life History of a Newly Discovered Alaska Surf Clam Resource
in the Southeastern Bering Sea
Steven E. Hughes and Neil Bourne 1205
Large Marine Gastropods of the Eastern Bering Sea
Richard A. Macintosh and David A. Somerton 1215
Feeding Interactions in the Eastern Bering Sea with Emphasis on the Benthos
Howard M. Feder and Stephen C. Jewett 1229
XIII: Interaction of Sedimentary and Water-column Regimes 1263
Interplay of Physical and Biological Sedimentary Structures of the Bering Continental Shelf
Hans Nelson, Robert W. Rowland, Sam W. Stoker, and Bradley R. Larsen 1265
XIV: Summary and Perspectives 1297
Consideration of Environmental Risks and Research Opportunities on the Eastern Bering Sea Shelf
Donald W. Hood and John A. Calder 1299
INDEX 1323
vn
Volume I Errata
On pa^^c 356, equations 2, 3, 4, 5, and 6 should
all have the term
-CO.
- (c:o, =i>pt)
In the Table of Contents of Volume One, the
name of Louis H. Barton should appear as second
author of the chapter in the Fisheries Oceanography
section entitled Distribution, Migration, and Status
of Pacific Herring.
On page 20, the figure numbers and legends are
reversed for Figures 2-7 and 2-8. Thus, the figure
designated 2-7 represents the summer weather
scheme, and 2-8 is the winter pattern.
On page 117, the last sentence should read:
Tidal type may be classified (e.g., Defant 1961)
by the value of the ratios of the sums of amplitudes
of principal diurnal constituents K, and O, to the
principal semidiurnal constituents M. and S. .
On page 126, in the first paragraph of the dis-
cussion, the comma after "Kelvin- waves near the
peninsula" should be a period, eind the following
words should be inserted:
In the mid-shelf region and along the Alaska
Peninsula, (the semidiurnal wave is progressive, etc.).
On page 130, the last item referred to should
read Cape Spencer.
On page 137, in Table 9-1, the second line should
read:
1976
-5.6
-2.3
-3.8
-2.5
On page 215, line 7, for "steady-state" read
'synoptic."
On pages 217 and 222, for "Parmenter" read
'Pcirmerter."
added to the end to account for that carbon dio.xide
lost to the system by biological or chemical precipi-
tation. This term is obtained experimentally by
measurement of alkalinity which is unaffected by
photosynthesis or respiration, whereas carbonate
removal also lowers alkalinity proportionately.
Equation 3 should read:
n(i)
F4 (ICO:^,, -CO:,,,) R„ CO:^
CO , =ppt)
Line 21, column 2, of page 356 should read:
This amount minus the 10 g of carbon exchanged
gives an estimate for respiration for the nine days
involved of approximately 3 gC/m- /day.
On page 402, left column, Cline and Holmes 1979
should be 1977.
On page 403, left column, line 3 should read:
There, the dominant homolog is 17q(H), 18q(H) ....
On page 406, Crisp et al. 1979 ... (in press)
should read 43:1791-1801, and on page 408,
Simoneit and Mazurek, 1978a, pages 565-70, and
1978b, pages 541-45.
On page 464, the last two sentences of the left
column should read:
An NWAFC tidal model study (Hastings 1975) in-
dicated that the reversals of flow are largely NE/SW
in inner Bristol Bay, between Nunivak and St.
Matthew islands and between St. Matthew Island and
the Gulf of Anadyr, and N\V/SE over much of the re-
mainder of the shelf (Fig. 29-9). Although these
flows have not been verified except in inner Bristol
Bay (Dodimead et al. 1963), the offshore/onshore
flow south of St. Matthew was apparently noted
by Dall (1882).
tx
fitl«
EaBtePi
Bopiiii E^h
"^anofip^j
Shelf:
11
and KesottPee
Section ¥1
Marine Birds
George L. Hunt, Jr., editor
I
Feeding Ecology of Seabirds
of the Eastern Bering Sea
George L. Hunt, Jr.,' Barbara Burgeson,' and
Gerald A. Sanger^
' Department of Ecology and Evolutionary Biology
University of California, Irvine
^ United States Fish and Wildlife Services
Biological Services Program— Coastal Ecosystems
Anchorage, Alaska
ABSTRACT
In this paper we review the current state of knowledge of
the trophic relations of seabirds of the eastern Bering Sea shelf
and provide new data obtained since 197 5. On the basis pri-
marily of foods used during the breeding season, it is clear that
a very few species of fish and invertebrates provide the major
portion of foods used in any one region, although the principal
prey species may vary from one region to another. In addition
to regional differences in prey use, seasonal and year-to-year
fluctuations in food habits are documented. Despite the rela-
tively narrow resource base used by the seabirds, there is con-
siderable evidence for resource partitioning.
The potential impact of seabird foraging on their prey pop-
ulations is discussed in the light of the consumption of be-
tween 5.8 and 11.5 \ 10"^ metric tons of food annually. The
consumption of juvenile walleye pollock by birds is estimated
to be about 50 percent of the tonnage of adult fish taken for
human consumption.
INTRODUCTION
In 1975, during an international symposium on the
conservation of marine birds of northern North
America, Ainley and Sanger (1979) identified three
particularly critical data needs pertaining to the tro-
phic relations of marine birds: (1) information on
foods used at times other than the breeding season;
(2) analysis of the trophic relations of the entire sea-
bird community, including migrant, nonbreeding
species; and (3) integration of trophic data from
seabirds into a holistic understanding of the dynamics
of the marine ecosystem. These goals have yet to be
attained, although a modest start has been made. Di-
voky (this volume) studied the ecology of seabirds at
the ice edge, including trophic relations, thereby pro-
viding our only knowledge of wintertime ecology.
629
Complementary studies during the breeding season by
several investigators have started to elucidate the tro-
phic relations of the Bering Sea seabird community as
a whole. These data will allow us to relate the pelagic
ecology of seabirds to the physical and biological
properties of the Bering Sea. This report presents
data on the diets of the seabirds of the Bering Sea
during the summer months (June-September).
Before the initiation of the Outer Continental
Shelf Environmental Assessment Program (OCSEAP)
in 1975, relatively little was known about the diets of
the marine birds of the Bering Sea. Ainley and San-
ger (1979) summarized the most important studies
of seabird diets available in the literature. These in-
cluded Swartz's (1966) study of nesting seabirds at
Cape Thompson in the Chukchi Sea, Bedard's
(1969a) study of auklets on St. Lawrence Island,
Preble and McAfee's (1923) survey of the seal:)irds of
the Pribilofs, and Ogi and Tsujita's (1973) examina-
tion of stomachs of birds caught in gillnets in Bristol
Bay. Of these, only Swartz (1966) and Bedard
(1969a) have sufficiently detailed quantitative data to
compare with data reported here.
A primary problem is to learn the functional role
of birds in the marine ecosystem. Detailed informa-
tion on the types and quantity of prey organisms
taken and their assimilation rates is necessary to un-
derstand this role. Information on diet allows us to
assess the trophic level at which the birds are for-
aging, and thus their role in cycling nutrients and
energy. To this end, identification of prey taken and
the relative use of prey types has proven feasible; we
630 Marine birds
have had less success in determining rates of con-
sumption, assimilation, and excretion. These param-
eters generally have been estimated on the basis of
untested assumptions.
As part of our attempt to understand the role of
birds in the marine ecosystem, we have tried to iden-
tify species of prey critical for the persistence of the
seabird colonies of the Pribilof Islands. Data from
other major Bering Sea colonies are needed, but in
most cases data are inadequate to tell if food require-
ments are similar to those at the Pribilofs, or to tell
the relative importance of prey species.
We can expect prey species to vary between colo-
nies (Biderman et al. 1978, Drury and Biderman
1978, Ramsdell and Drury 1979) and we should not
assume that prey selection is constant from one re-
gion to another, or from one year to the next. When
we learn what the variations in diet are, and can com-
bine this knowledge with information on population
dynamics and reproductive success, we will be able to
learn the functional role of seabirds in the marine
ecosystem (Biderman et al. 1978, Drury and
Biderman 1978, Ramsdell and Drury 1979).
A second problem of interest to ecologists is how
co-existing organisms partition critical resources. Par-
titioning of food resources may consist of taking dif-
ferent species and sizes of prey, or of foraging for
prey in different places or with different methods. If
food requirements and foraging methods are suffi-
ciently distinct, interspecific trophic competition in
multispecies colonies is reduced. The opportunity to
obtain dietary information from many species simul-
taneously in large multispecies colonies has made it
possible to examine the ways in which seabirds parti-
tion prey. Partitioning of food resources by prey size
and foraging habitat will be dealt with elsewhere.
This chapter summarizes the data on seabird prey
preferences gathered during the OCSEAP studies in
the Bering Sea in 1975-78. We also attempt to com-
paire these results with other studies from the Bering
Sea and, when relevant, with studies of the same spe-
cies in other areas. This chapter provides brief ac-
counts of the foraging methods of each species and
tables of the most important kinds of foods taken on
the bases of percent occurrence, percent volume, and
percent numbers. Prey items constituting less than 5
percent of the diet by all of these measures are com-
bined under "Other," except for prey species which
we wish to compare between regions.
Seasonal changes in diet are illustrated for three
species to show how diets may change throughout
the breeding season, in response either to changes in
the availability of a preferred item, or to changes in
physiological needs as birds shift from the incubation
of eggs to the feeding of chicks.
METHODS
Food samples were obtained in the field, either by
collecting adults or from the regurgitations of chicks,
and preserved. In the laboratory, the samples were
sorted, identified to lowest taxon possible, and
counted. Displacement volumes were measured
after draining (Pribilof Islands samples) or estimated
visually.
Percent occurrence was determined for each bird
species on the basis of the percentage of samples in
which a prey type occurred. Since several different
prey types might occur in a single sample, the sum of
the percent occurrences is greater than 100 percent.
Percent volume was calculated by dividing the sum of
the volumes of a particular prey type from all samples
by the total volume of all samples combined. Percent
individuals was calculated by dividing the total num-
ber of individuals of a particular prey taxon by the
number of all prey individuals recovered from a par-
ticular bird species.
These three measures provide complementary
types of information about diets and allow the meixi-
mum opportunity to relate our results to those of
other investigators. Pinkas et al. (1971) used these
three measures in calculating an Index of Relative
Importance, and discussed their individual limita-
tions. Percent occurrence tends to overestimate prey
with persistent hard parts. Percent volume, on the
other hand, overestimates items that may be slow to
be digested, and quickly digested prey, whether or
not they have hard parts, are underestimated.
RESULTS
Northern Fulmar (Fulmarus glacialis)
Fulmars obtain their food at or near the surface of
the water (Ashmole 1971; Ainley and Sanger 1979;
G. Hunt, personal observation). Although fulmars are
widely distributed in the southeastern Bering Sea,
their principal foraging concentrations are along the
shelf break (Hunt et al.. Chapter 40, this volume). Be-
cause of their knovm preference for feeding on offal
from fishing vessels (Fisher 1952), relatively little ef-
fort was made to collect this species. This may have
been an error, as the stomachs which were collected
showed a wide vairiety of natural foods (Table 38-1).
Of the 10 fulmars collected, 1 came from St. Paul, 4
from St. George, and 5 from the southeastern Bering
Sea about 105 km north of the Alaska Peninsula.
Although fulmars made a greater use of cephalo-
pods than any other bird species studied, they also
made heavy use of walleye pollock (Tlieragra chalco-
gramma). Some of these pollock may have been scav-
enged from fishing fleets. On the other hand, the
Feeding ecology of sea birds 631
TABLE 38-1
Foods of Northern Fulmars
Pribilof Islands and Southeastern Bering Sea, 1975-78
N = 10
%
%
%
Species
occurrence
vol
number
Cephalopoda
40.0
21.2
32.3
Crustacea
10.0
3.0
2.9
All Euphausiidae
10.0
3.0
5.9
All fish
70.0
72.7
58.8
Theragra chalcogramma
10.0
60.6
11.8
pelagic distribution of fulmars coincides with an area
in which one might expect large numbers of pollock
(based on fishing effort). We are left without a good
idea of the present-day natural diet of fulmars be-
cause there is no way of distinguishing foods obtained
in conjunction with fishing operations from those ob-
tained independently of man. Fulmars were also ob-
served foraging on jellyfish (Preble and McAtee 1923;
G. Hunt, personal observation), although it is difficult
to judge the importance of this food in their diets.
Our findings closely agree with those of others.
Preble and McAtee (1923) stressed the use of cepha-
lopods by fulmars during a period before there were
major fishing operations in the Bering Sea, and later
authors dealing with Alaskan waters or the north At-
lantic emphasized the use of fish offal in addition to
cephalopods (Gabrielson and Lincoln 1959, Fisher
1952). Among OCSEAP investigators, only G. Hunt,
G. Sanger, and D. Forsell (U.S. Fish and Wildlife Ser-
vice) gathered data on fulmar diets in the Bering Sea.
Short-tailed and Sooty Shearwaters (Puffinus tenui-
rostris, P. griseus)
Short-tailed and Sooty Shearwaters nest in the
southern hemisphere; Sanger and Baird (1977b) esti-
mated that approximately seven million Short-tailed
and three million Sooty Shearwaters spend the north-
em summer in the Bering Sea. Recently this estimate
was increased to a minimum of nine million shear-
waters in the eastern Bering Sea alone; of these 10
percent were estimated to be Sooty Shearwaters
(Hunt et al.. Chapter 39, this volume). These species
forage primarily by pursuit plunging (Sealy 1973,
Ainley and Sanger 1979, Brown et al. 1978), by hy-
droplaning (Sealy 1973), and by surface seizing (G.
Hunt, personal observation). Their foraging is be-
lieved to be restricted to the upper 5 m of the water
column (Sanger 1972), on the basis of observations of
birds drowned in gillnets.
Recent unpublished data (Sanger, U.S. Fish and
Wildlife Service) indicate that the diet of Short-tailed
Shearwaters in the Bering Sea in summer was over 70
percent euphausiids, while in fall over 60 percent of
the diet was the large hyperiid amphipod, Parathemis-
to libellula. Cephalopods and fish were also moder-
ately important in both seasons. Past records of
foods used by shearwaters were summarized by Ain-
ley and Sanger (1979). Both Short-tailed and Sooty
Shearwaters consume a variety of euphausiids, cepha-
lopods, fish, and carrion (Ainley and Sanger 1979).
Sanger and Baird (1977a) compared the stomach con-
tents of 11 Short-tailed Shearwaters and 22 Sooty
Shearwaters from the Gulf of Alaska and 12 Short-
tailed Shearwaters from the Bering Sea. The Sooty
Shearwaters contained large numbers of squid and
fish and only a very small amount of euphausiids; fish
and squid were less important for Short-tailed Shear-
waters, which took large amounts of euphausiids.
The size of the major prey selected by the two species
of shearwaters was strikingly different, with the fish
taken by Sooty Shearwaters averaging 121 mm (range
80-137) while the euphausiids preferred by the Short-
tailed Shearwaters averaged 25 mm (range 14-32).
However, Sanger et al. (1978) showed that both spe-
cies of shearwaters in the Kodiak area ate capelin
(Matlotus uillosus) of the same size, which were ap-
parently extremely abundant and available to the
birds in the spring and summer of 1977. Additional
data on these biologically dominant species of birds
are required to determine if they do partition food re-
sources by size or prey type and to understand their
role in the Bering Sea ecosystem.
Fork-tailed Storm-Petrel (Oceanodroma furcata)
Fork-tailed Storm-Petrels forage by dipping
and seizing food while sitting on the water's surface
(Ashmole 1971, Ainley and Sanger 1979). They con-
centrate their foraging seaward of the 100-m curve in
the southeastern Bering Sea, and are seldom seen
north of 57° (Hunt et al.. Chapter 39, this volume).
The one full stomach of this common pelagic bu'd
that was obtained in the Bering Sea contained squid.
Preble and McAtee (1923) claimed that Fork-tailed
Storm-Petrels take fish, and our observations of their
attendance upon fishing vessels suggest that they may
take offal as well (see Ainley and Sanger 1979). The
review of eastern North Pacific literature for this spe-
cies (Ainley and Sanger 1979) showed that, in addi-
tion to the above items, euphausiids also may be
important. Clearly, we need more data on the diet of
this species in the Bering Sea.
632 Marine birds
Red-faced Cormorant (Phalacrocorax urile)
Red-faced Cormorants forage by diving, and cap-
turing fish and crustaceans under water (Ainley and
Sanger 1979). Most records of cormorant foraging
come from the immediate vicinity of their colonies or
roosts (Sowls et al. 1978; Hunt et al., Chapter 39, this
volume; Hunt et al.. Chapter 40, this volume), a result
of their need to leave the water for frequent periods
to dry out their feathers.
Table 38-2 provides a summary of the diet of Red-
faced Cormorants at the Pribilof Islands during the
period 1975-78. Their primary source of food was
TABLE 38-2
Foods of Red-faced Cormorants
Pribilof Islands, 1975-78
N= 169
rv
/r
7o
7c
Species
occurrence
vol
number
All amphipods
23.7
0.4
19.9
All decapods
55.6
14.8
30.1
All fish
96.5
84.3
43.2
Thcragra chalcograinnia
6.5
3.2
2.2
Cottidae
17.7
12.2
8.9
Aminudytcs licxaplcrus
5.3
5.2
4.0
fish, and of the remains identified, cottids were taken
more often than other types. A wide variety of large
decapods was taken, including shrimp and crabs.
Preble and McAtee (1923) found in five stomachs col-
lected on the Pribilofs that 58 percent of the food
was fish and 41 percent crustaceans; cottids were the
most frequently taken fish, and shrimp the pre-
dominant invertebrate. All indications are that Red-
faced Cormorants forage near the bottom close to
land, and probably have little effect on the marine
ecosystems of the Bering Sea.
Pelagic Cormorant (Phalacrocorax pclagicus)
Pelagic Cormorants nest for the most part in the
northern Bering Sea (Sowls et al. 1978), and in the
winter probably move southward throughout the
southeastern Bering Sea. Although they may occa-
sionally nest, or have nested, at the Pribilofs, most
records are for the fall or winter (Preble and McAtee
1923, and others).
No samples of the diet of Pelagic Cormorants were
obtained by OCSEAP investigators working in the
Bering Sea. Preble and McAtee (1923) collected 21
stomachs of this species in the Pribilofs, mostly
during the winter, and found that 74 percent of the
diet was fish and 26 percent Crustacea. Cottids were
the most frequently taken fish, and 86 percent of the
stomachs contained shrimp. There appears to be
some difference in the species of cottids taken by the
two cormorants at the Pribilofs (Preble and McAtee
1923), but without quantitative data, it is impossible
to assess the importance of these differences.
Fish and shrimp were the principal components of
the diet in the stomachs of two Pelagic Cormorants at
Cape Thompson (Swartz 1966). These results from
Cape Thompson and the Pribilofs agree with the sum-
mary of information of the foods of Pelagic Cormo-
rants provided by Ainley and Sanger (1979).
Black-legged Kittiwake (Rissa tridactyta)
Black-legged Kittiwakes nest throughout the Bering
Sea wherever there are suitable cliffs. The size of lo-
cal populations appears to be determined largely by
the availability of nest-sites (Hunt et al.. Chapter 40,
this volume). Black-legged Kittiwakes forage in low
densities (Hunt et al.. Chapter 39, this volume), by
dipping (Sealy 1973, Ainley and Sanger 1979), or
surface seizing (Sealy 1973; G. Hunt, personal obser-
vation), and occasionally by shallow pursuit plunging
(Gould and Sanger, U.S. Fish and Wildlife Service, un-
published). These birds are unable to obtain food
from more than 0.5 m below the surface.
Table 38-3 provides a summary of the commonly
taken food items obtained from Black-legged Kitti-
wakes in the Pribilof Islands from 1975 to 1978.
Fish were by far the most important food taken, with
walleye pollock the predominant species in the diet
of Black4egged Kittiwakes. Capelin and myctophids
were also taken, but less frequently than pollock.
Preble and McAtee (1923) collected only three Black-
legged Kittiwake stomachs at the Pribilofs and one at
St. Matthew Island, and provide few data of value.
There was a marked seasonal variation in the use of
food by Black-legged Kittiwakes in the Pribilofs
(Table 38-4). In June, before eggs are laid, inverte-
brates, particularly the amphipod P. libellula and eu-
phausiids, were the primary food source for Black-
legged Kittiwakes. In July, during incubation, the
frequency and volume of fish, especially walleye pol-
lock and myctophids, increased, while the use of
invertebrates decreased. Of the identified euphausiids
taken, 95 percent were Thysanoessa inermis or T.
longipes and 5 percent T. raschii. Myctophids, T.
incrniis, and T. longipes are found near the shelf
break, and their inclusion in the diet means that
birds were probably commuting long distances (up to
100 km from St. Paul) to forage. In August and
September, when most food samples were obtained as
Feeding ecology of seabirds 633
TABLE 38-3
Foods of Black-legged and Red-legged Kittiwakes
Pribilof Islands, 1975-78
Black-legged Kittiwake N = 605
Red-legged Kittiwake N = 376
Species
% occurrence
BLK
RLK
% volume
BLK
RLK
% number
BLK
RLK
Cephalopoda
Paralhcmisto libeltula
All Euphausiidae
Thysanocssa raschii
All fish
Ammodylcs hcxaptcrus
Mallotus villosus
Myctophidae
Thcragra chalcogramma
5.6
16.8
1.0
1.9
0.5
5.8
13.1
3.5
2.7
0.5
9.4
10.1
10.3
3.7
4.6
0.5
34.5
5.2
5.0
1.3
2.1
0.3
16.7
2.8
88.6
87.8
89.3
95.5
19.8
63.2
4.6
0.5
3.1
0.3
1.2
0.2
12.7
1.6
9.6
1.3
1.5
0.4
11.2
58.2
11.3
57.2
1.8
38.8
38.2
18.6
45.5
23.8
10.2
15.4
regurgitations from chicks, walleye pollock predomi-
nated; myctophids, T. inermis, and T. longipes
decreased, while T. raschii increased. In August T.
raschii represented 82 percent of the identified eu-
phausiids and in September, 96 percent. The de-
crease in the use of myctophids, T. inermis, and T.
longipes and the increase in walleye pollock and T.
raschii, which are found on the shelf, suggest either
that foods requiring long foraging trips were avoided
while chicks were being fed or that there was a signifi-
cant increase in the availability of pollock and T.
raschii near the colony during the chick stage.
The size of walleye pollock taken by Black-legged
Kittiwakes changed through the breeding season
(Fig. 38-1). Early in the season (July) fish 13-18 cm
were common and these were probably fish of the
previous year's cohort (Cooney et al. 1978). In Au-
gust and September, fish of the year predominated in
kittiwake food samples, and pollock growth can be
demonstrated by the shift from a length of < 5-6 cm
to 6-8 cm. Pollock lengths were calculated using the
relationship of otolith length vs. fish length deter-
mined by Frost and Lo^rry (in preparation).
It is not known why pollock and other fish were
not eaten more extensively in June; it is possible that
they were not available. An alternative hypothesis is
that Parathemisto and euphausiids are easier to ob-
tain, or that there is less competition for them and
they are taken in preference to fish until a point in
the breeding cycle when the higher nutritional values
of fish are required.
In discussing competitive relations between species
in seabird colonies, Belopolskii (1957) comments
that invertebrates are less valuable than fish to Black-
legged Kittiwakes for raising young. He found that,
when kittiwakes in the Barents Sea colonies were
forced to rely heavily on invertebrates, they laid
TABLE 38-4
Monthly variation in Black-legged Kittiwake food habits
Pribilof Islands, 1975-78
Total percent volume
June
July
Aug
Sept
N
44
128
298
109
Cephalopoda
3.3
0.9
1.1
0.5
Parathemisto libellula
27.7
4.2
1.7
2.5
All Euphausiidae
21.0
12.1
2.5
4.1
Thysanocssa inermis
5.9
2.4
0.4
0.4
Thysanocssa longipes
0.0
2.5
0.0
0.0
Thysanocssa raschii
1.7
0.2
1.9
3.6
All fish
45.4
77.9
93.6
89.2
Ammodylcs hcxaptcrus
0.0
1.7
2.4
5.7
Mallotus villosus
0.0
1.7
9.9
13.0
Myctophidae
10.1
28.5
9.5
5.3
Thcragra chalcogramma
0.0
27.0
50.5
49.1
634 Marine birds
E
z
u
_l
X
p
28-1
27-
26-
25
24
23-
22-
21-
20-1
19-
18-
17
16
15
14
13
12-
11-
10-
9-
8-
7-
6-
5-
<5
I From adult stomachs Q From chick regurgitations
JULY AUGUST SEPTEMBER
20 30 40 50
n 1 1 1 r-
10 20 30 40 50
I
J
^ I I I I
10 20 30 40 50
% of pollock found in sample
Figure 38-1. Changes in size of walleye pollock (Theragra chalcogramma) taken by Black-legged Kittiwakes on the Pribilof
Islands.
smaller clutches (p. 267), and had lower chick sur-
vival (p. 262). Thus, although Black-legged Kitti-
wakes may take a great variety of foods, there may
be some important restrictions on the types of
foods they must have if they are to reproduce suc-
cessfully.
Biderman et al. (1978) and Drury and Biderman
(1978) provide qualitative information on Black-
legged Kittiwake foraging in the Bering Strait and
along the south side of the Seward Peninsula. At
Little Diomede Island, Black-legged Kittiwakes rarely
foraged near land until late June, when large flocks
(4,000-8,000) foraged over a shallow bar, presumably
on Crustacea. Nearshore melees of foraging kitti-
wakes were also seen near Bluff on the Seward Penin-
sula. Foraging patterns there suggest a seasonal
change in food habits similar to that seen in the Prib-
ilofs. In early and mid-June, small fish were taken; in
July, Crustacea seemed to be the principal prey. In
August, prey fed to Black-legged Kittiwake chicks
were small (3-5 cm) sand lance (Ammodytes sp.). The
availability of abundant shoals of these fish may be
critical to kittiwake reproductive success in the north-
em Bering Sea (Drury and Biderman 1978, Ramsdell
and Drury 1979).
At Cape Thompson, Swartz obtained samples from
both Black-legged Kittiwake adults and chicks (Table
38-5); he did not specify whether adult foods were
sampled before or during the chick phase. Fish were
clearly most important to this population, particu-
larly sand lance and Arctic cod (Boreogadus saida),
which appear to replace walleye pollock at this high
latitude. Significantly more invertebrates were taken
at Cape Thompson than in the Pribilofs, and many
types of prey used in the Pribilofs were not used at
Cape Thompson (cephalopods, euphausiids, Parathe-
Feeding ecology of seabirds 635
TABLE 38-5
Foods of Black-legged Kittiwakes at Cape Thompson
(Swartz 1966)
Percent occurrence
Adults
Chicks
N
92
39.5
All invertebrates
25.0
0.0
Cephalopoda
0.0
0.0
Parathemisto libellula
0.0
0.0
Euphausiidae
0.0
0.0
Polychaetes
5.4
0.0
All fish
91.4
81.4
Ammodytes
29.3
65.1
Mallotus villosus
2.2
0.0
Myctophidae
0.0
0.0
Theragra chalcogramma
0.0
0.0
Boreogadus saida
54.3
23.3
misto, myctophids, Theragra), presumably reflecting
their different geographic ranges.
Red-legged Kittiwakes (Rissa hreuirostris)
The breeding distribution of the Red-legged Kitti-
wake is unusually restricted; 88 percent of the world
population breeds on the high cliffs of St. George
Island, with additional small eastern Bering Sea colo-
nies on St. Paul and Otter islands in the Pribilofs, and
on Bogoslof and Buldir islands in the Aleutians
(Sowls et al. 1978; Hunt et al., Chapter 40, this vol-
ume). This species forages by dipping (Ainley and
Sanger 1979) and by shallow plunge diving (G. Hunt,
personal observation).
Although the general types of foods used by Red-
legged Kittiwakes (Table 38-3) are similar to those
used by Black-legged Kittiwakes, there are striking
differences in particular food types between these
two species. In particular. Red-legged Kittiwakes use
myctophids heavily, which undoubtedly accounts for
the fact that their pelagic distribution is concentrated
near the shelf break, and for the fact that all their
colonies are close to the shelf edge.
Preble and McAtee (1923) examined 15 stomachs
from St. George Island (dates of collection not speci-
fied). Seven of the stomachs contained only squid
mandibles. In eight of the stomachs containing mea-
surable volume, 25 percent of the food present was
squid, 37.5 percent Crustacea, and 37.5 percent fish.
The Crustacea were chiefly euphausiids of the genus
Thysanoessa. These results vary from our own, but
the differences may result from the small size of their
sample, or may reflect seasonal differences in the diet
of this species, or even, after 55 years, differences in
prey availability.
Data on seasonal changes in Red-legged Kittiwakes
in the period 1975-78 show a drop in the use of
cephalopods and an increase in the use of fish, par-
ticularly myctophids, as the season progressed (Table
38-6). It is interesting that there was a drop in the
use of pollock during the season, followed by a sharp
increase in September. This pattern differs from that
seen in Black-legged Kittiwakes (Table 38-4). The
early season use of pollock by Red-legged Kittiwakes
may reflect their foraging near the shelf break to a
greater extent than Black4egged Kittiwakes. Red-
legged Kittiwakes also consumed much less P. libel-
lula, a shallow-water eastern shelf species (Motoda
and Minoda 1974), than Black-legged Kittiwakes,
particularly early in the breeding season.
Common Murre (Uria aalge)
Common Murres breed throughout the coasts
and islands of the Bering Sea where there are fox -free
cliffs with wide ledges to support their colonies
(Sowls et al. 1978; Hunt et al.. Chapter 40, this
volume). They forage primarily by diving (Ainley
and Sanger 1979).
Table 38-7 provides a summary of the important
foods used by Common Murres on the Pribilof Is-
lands. As might be expected from the predictions of
Spring (1971), fish were the principal component of
their diet. Of these, walleye pollock was the single
most important species. Preble and McAtee (1923)
reported on the contents of 18 stomachs, mostly
TABLE 38-6
Monthly variation in Red-legged Kittiwake food habits
Pribilof Islands, 1975-78
Percent volume
June
July
Aug
Sept
N
43
69
124
108
Cephalopoda
16.8
1.4
2.7
0.3
Paralhcmisto libellula
0.0
0.2
0.1
0.9
All Euphausiidae
0.0
2.5
0.3
0.1
Thysanoessa raschii
0.0
1.6
0.2
0.1
All fish
83.2
93.2
95.4
97.5
Ammodylcs hexaptcrus
0.0
0.0
0.8
0.0
Mallolus villosus
0.0
3.2
0.8
1.3
Myctophidae
30.8
73.4
59.6
47.9
Theragra chalcogramma
14.2
5.7
17.3
36.6
636 Marine birds
TABLE 38-7
Foods of Common and Thick-billed Murres
Pribilof Islands, 1975-78
Common Murre N = 117
Thick-billed Murre N = 233
% occurrence
% volume
% number
Species
CM TbM
CM TbM
CM TbM
Cephalopoda
Polychaetes
All amphipods
Parathemisto libellula
All Euphausiidae
All fish
Ammodytes hexaptcrus
Mallotus uillosus
Myctophidae
Theragra chalcogramma
Triglops pingeli
Stichaeidae
5.1
11.2
2.6
1.3
8.5
23.6
4.3
20.2
3.4
13.3
95.7
82.0
0.9
3.9
5.1
3.0
0.9
1.3
39.3
40.3
0.0
4.3
1.7
0.9
1.2
5.3
0.0
0.1
1.5
10.4
1.3
9.7
2.1
6.7
95.2
76.0
0.5
1.1
8.7
1.8
0.0
0.4
56.2
39.6
0.0
6.4
10.1
0.5
0.3
1.3
0.2
1.0
1.0
19.6
0.8
19.1
58.5
45.9
39.8
31.8
0.0
0.3
0.2
0.2
0.2
0.2
21.2
18.4
0.0
0.3
0.1
0.1
taken in winter. In contrast to our results, they
found the 12 stomachs with food contained almost
exclusively amphipods, particularly Pontogenia, with
lesser numbers of other species. One stomach con-
tained nereid worms. Only the nearly empty stom-
achs had traces of small sculpins (Cottidae). These
data differ from most others, mainly gathered during
the breeding season. The question remains whether
Preble and McAtee's result was due to the small size
of their sample or real differences in the diets of
Common Murres in summer and winter.
At St. Lawrence Island, Searing (1977), in a sample
of five stomachs, found Common Murres using both
invertebrates and fish. Ramsdell and Drury (1979),
working at Bluff on the south coast of the Seward
Peninsula found adult Common Murres taking sand
lance 3-5 cm in length for themselves, but bringing
various pricklebacks (Lumpenus) to their chicks.
They made no mention of the use of invertebrates.
Further north, at Cape Thompson on the Chukchi
Sea, Swartz (1966) examined 86 stomachs of Com-
mon Murres (Table 38-8). The diet of Common
Murres there, like those at the Pribilofs in summer, is
almost exclusively fish, with Boreogadus saida replac-
ing pollock as the single most important species. At
Cape Thompson, the diets of adult Common Murres,
unlike those in the Pribilofs, contain an important
component of sand lance (Ammodytes). This use of
Ammodytes in the north is similar to the pattern of
food preference shown by the Black-legged Kitti-
wake, in that Ammodytes axe seldom used at the
PribUofs, but are an important part of the kittiwake
diet in Norton Sound and at Cape Thompson. The
use of Ammodytes in the north may not represent a
north-south distribution, but rather their greater
abundance in coastal versus pelagic habitat. The data
from the Bering and Chukchi Seas are similar to those
obtained by Belopolskii (1957), who found that 95
percent of the diet of Common Murres found in the
Barents Sea consisted of fish.
Thick-billed Murre (Uria lomvia)
Thick-billed Murres nest throughout the Bering Sea
where cliffs vdth narrow ledges afford protection
from foxes (Sowls et al. 1978; Hunt et al.. Chapter
40, this volume). They are more abundant on islands
near the shelf edge than at mainland cliffs such as
Cape Peirce (Dick and Dick 1971, Sowls et al. 1978).
Thick-billed Murres forage primarily by diving for
prey (Ainley and Sanger 1979).
Table 38-7 provides a summary of foods used by
Thick-billed Murres on the Pribilof Islands. Although
fish, particularly the walleye pollock, were the most
Feeding ccolofiy of scahirds 63 7
TABLE 38-8
Foods used by Common and Thick-billed Murres
at Cape Thompson (Swart/, 1966)
Percent occurrence
Th
ick-
Com
mon
billed
Murres
Murres
adults
chicks
adults
chicks
N
84
2
176
11
Invertebrates
6.1
0.0
33.8
25.0
Polychaetes
6.1
0.0
9.0
0.0
Moliusca
Naticidae
0.0
0.0
5.3
0.0
Fish
95.5
100.0
63.9
100.0
Ammodytes
27.3
50.0
0.8
0.0
Mallotus villosus
0.0
0.0
0.0
0.0
Boreogadus saida
77.3
50.0
45.1
57.1
Myoxocephalus quadricornis
0.0
0.0
4.5
14.3
Chirolophis polyactocephalus
1.5
0.0
0.8
14.3
Stichaeus punctatus
0.0
0.0
0.8
14.3
Ly codes sp.
0.0
0.0
0.0
14.3
Pleuronectidae
6.1
50.0
2.3
0.0
important foods for this species, invertebrates also
figured significantly in their diet. Of the inverte-
brates taken, Parathemisto libellula predominated.
Our data indicate that the diets of Thick-billed
Murres may vary seasonally (Table 38-9). Early in
the season before eggs were laid and late in the sea-
son after chicks left the cliffs, invertebrates assumed a
more important role, and fish dropped from over 70
percent of the diet to less than 30 percent. The
heavy use of fish in August may reflect the provision
of fish to young, but that is unlikely to be the reason
for the heavy use of fish in July, when most breeding
birds were incubating (Hunt et al. 1978; Hunt et al..
Chapter 40, this volume). In June, most invertebrates
taken were euphausiids or amphipods; and our small
sample from September indicates that cephalopods
may then have made up the largest portion of the
diet. Preble and McAtee (1923) found in six Thick-
billed Marre stomachs 49 percent fish, 26 percent
squid, and 25 percent crustaceans. The dates when
these birds were collected were not given.
At Cape Thompson (Table 38-8), Swartz (1966)
found that Thick-billed Murres depended upon in-
vertebrates, in addition to fish, as they did in the
Pribilofs. Again, the principal fish taken was a gadid.
Boreogadus saida, but unlike at the Pribilofs, the
most important invertebrates were polychaete worms.
Searing (1977) obtained 12 stomachs with food from
Thick-billed Murres at Kongkok Bay, St. Lawrence
Island, between 9 and 18 June 1976. The item most
commonly taken was the decapod Eualus fabricii,
followed by the amphipod Anonyx nugax. Fish were
present in only three of the birds. In the Barents Sea,
invertebrates constituted only 5-15 percent of the
diet (Belopolskii 1957, pp. 46, 95), in the North At-
lantic 6 percent (Tuck 1960).
A comparison of the diets of the two species of
murres (Table 38-8) demonstrates clearly that Thick-
billed Murres use more invertebrates than Common
Murres. Swartz (1966) and Tuck (1960) found simi-
lar patterns of greater rehance on invertebrates by
Thick-billed Murres; this conclusion agrees with those
of Spring (1971) drawn on the basis of m.orphology.
Somewhat surprisingly, Belopolskii (1957) showed no
major differences in percentage of invertebrates used
between the diets of the two species of murres.
Ogi and Tsujita (1973) examined the stomachs of
163 murres caught in high-seas gillnets in the eastern
Bering Sea and Bristol Bay in June-August 1970 and
1971. Since these authors did not report their find-
ings according to the species of murre from which
samples were obtained, their data are of limited value.
However, they did show that of 131 stomachs con-
taining food, 44 percent had fish, 26 percent euphau-
siids, and 11 percent squid. On a percent weight
basis, fish were by far the most important prey taken.
Species of fish taken included walleye pollock, sand
lance, and capelin. Two species of euphausiids were
used, Thysanoessa raschii and T. longipes; T. inermis
was not observed.
TABLE 38-9
Monthly changes in foods u.sed by Thick-billed Murres
Pribilof Islands, 1975-78
Total percent volume
June
July
Aug
Sept
N
46
84
101
5
Cephalopoda
0.0
1.3
5.8
44.4
All Amphipods
10.0
13.3
6.3
0.0
Parathemisto libellula
8.9
12.7
5.8
0.0
All Euphausiidae
25.7
9.1
0.4
0.0
All fish
27.6
79.8
73.7
29.6
Ammodytes hexapterus
0.2
2.3
0.6
0.0
Theragra chalcogramma
9.1
39.7
41.2
0.0
Other
36.7
1.5
13.7
25.9
638 Marine birds
Small auklets
Three species of small auklets are common in the
eastern Bering Sea from the Aleutian Islands to the
Bering Straits: the Parakeet Auklet (Cyclorrhynchus
psittacula), the Crested Auklet (Aethia cristatella),
and the Least Auklet (A. pusilla). The Cassin's Auk-
let (Pty choramphus aleuticus) and Whiskered Auklet
(A. pygmaea) that occur along the Aleutian chain
will not be discussed here.
The Parakeet Auklet has the widest distribution of
the auklets in the eastern Bering Sea. It occurs not
only on the shelf edge and northern islands with the
Crested and Least Auklets, but also in cliff colonies
along the mainland (Bedard 1969a; Sowls et al. 1978;
Hunt et al., Chapter 40, this volume). The Crested
and Least Auklets nest primarily in talus slopes; the
Parakeet Auklet prefers crevices in cliffs (Bedard
1969b). There appears to be suitable nesting habitat
available for the talus nesting species which is not
used (Hunt et al., Chapter 40, this volume; W. Drury,
College of the Atlantic, personal communication).
All three species of auklets feed primarily by diving
(Ainley and Sanger 1979).
Table 38-10 provides a summary of the most im-
portant foods used by auklets in the Pribilof Islands
1975-78. These results can be compared with those
of Bedard (1969a) and Searing (1977) for St. Law-
rence Island, the only other Bering Sea location for
which extensive data exist on the food habits of
these small auklets. Data from the Pribilofs in 1975-
78 were gathered primarily during the chick phase
and represent gular-pouch loads being brought to
chicks.
In the Pribilofs the Parakeet Auklet, a generalist,
used three types of food extensively— euphausiids,
fish (primarily larval fish), and polychaetes— and
made moderate use of amphipods. In contrast, the
Crested Auklet appeared highly specialized on eu-
phausiids and somewhat less specialized on amphi-
pods, while the Least Auklet was highly specialized
on calanoid copepods and much less on amphipods.
When Preble and McAtee (1923) gathered material in
the early 1900's, they reported similar food prefer-
ences for these auklets, although for the most part
their data were very sketchy.
Searing's (1977) data from St. Lawrence Island and
those of B6dard (1969a) were collected approximate-
ly ten years apart. Both of these studies showed that
Least Auklets depend primarily on Calanus during the
chick phase. However, the two studies found a differ-
ence in the diets of Crested Auklets. Bedard 's
(1969a) work showed Crested Auklets taking pri-
marily euphausiids (56 percent) and smaller numbers
of calanoids (36 percent), while Searing's (1977)
study indicated that over 97 percent of the diet con-
sisted of calanoids. These differences may reflect
yearly fluctuations in the availability of prey species.
Parakeet Auklets were not studied by Searing, but
Bedard found them to be generalized foragers taking
a wide variety of midwater and epibenthic foods, par-
ticularly calanoids, euphausiids, and amphipods. Al-
though Parakeet Auklets took more fish than the
other auklets, fish were still only a minor portion of
their diet on St. Lawnrence Island (Bedard 1969a).
The comparison of data from the Pribilof Islands
and St. Lawrence Island shows three important fea-
tures of the food habits of these small auklets.
(1) The three small auklets partition food re-
sources by taking different types and sizes of prey
and by feeding in different habitats. The Least Auk-
let takes the smallest items, the Crested Auklet the
next largest, and the Parakeet Auklet the largest.
These patterns, first found by Bedard (1969a) on St.
LaviTcnce Island, were found on the Pribilof Islands
in the present study (Hunt et al. 1978).
(2) Of the three species of auklets, two, the Least
and the Crested Auklets, are specialized foragers on
zooplankton in middle and surface depths, while the
third, the Parakeet Auklet, takes a wider variety of
plankton, invertebrates, and fish, at least some de-
mersally or epibenthically. These differences in diet
may have important implications for determining the
distribution of these species of birds. Bedard (1969b)
and Hunt et al. (Chapter 40, this volume) discuss how
the ranges of the Crested and Least Auklets are re-
stricted to islands near water masses with zooplank-
ton characterized by large shelf-edge forms. Converse-
ly, the widespread Parakeet Auklet occurs in coastal
waters accessible to demersal/epibenthic forms and
where large calanoids may be absent, or harder to
catch due to increased turbidity.
(3) The patterns of food preference discussed
above appear relatively stable over several years in the
colonies studied. Calanoids were of primary impor-
tance for Least Auklets in all three studies of foods
brought to chicks, although Bedard's (1969a) study
showed that before the chick phase they used a more
diverse diet. Crested Auklets in the two multiyear
studies showed a strong preference for euphausiids,
although in Searing's (1977) one-year study, the 12
birds sampled showed a preference for calanoids, a
group of prey found by the other studies to be taken
in smaller quantities. In the more generalized Para-
keet Auklets, the species of foods varied between
studies, most likely reflecting the ability of this spe-
cies to shift among a variety of prey.
Feeding ecnloRy of seabirdf; 639
TABLE 38-10
Foods of Parakeet, Crested, and Least Auklcts
Pribilof Islands, 1975-78
Parakeet Auklet N =
55
Crested Auklet N =
20
Least Auklet N =
258
%
occurrence
% volume
%
number
Species
PA
CA
LA
PA
CA
LA
PA
CA
LA
Polychaetes
23.6
0.0
0.4
23.5
0.0
0.0
21.9
0.0
0.0
All Calanus
10.9
0.0
59.7
4.1
0.0
73.5
21.6
0.0
93.4
Calanus cristatus
9.1
0.0
34.1
3.7
0.0
10.8
21.6
0.0
4.7
Calanus marshallae
0.0
0.0
11.2
0.0
0.0
22.1
0.0
0.0
18.6
Calanus plumchrus
0.0
0.0
14.3
0.0
0.0
0.7
0.0
0.0
3.1
All amphipods
25.5
35.0
55.0
12.2
29.6
15.1
15.3
41.6
4.0
Parathemisto libellula
16.4
25.0
32.2
10.1
20.3
8.6
14.5
35.4
2.2
All Euphausiidae
23.6
60.0
19.8
32.2
68.7
4.1
32.5
56.3
0.6
Thysanoessa inermh
5.5
15.0
1.5
10.1
33.4
0.0
12.4
38.4
0.0
Thysanoessa raschii
9.1
10.0
6.2
19.4
7.5
1.6
12.3
6.3
0.1
All fish
40.0
25.0
9.7
26.6
0.8
0.7
8.3
1.1
0.1
Theragra chalcogramma
9.1
0.0
0.4
4.5
0.0
0.3
3.6
0.0
0.0
Horned Puffin (Fratercula corniculata)
Homed Puffins nest in crevices in cliff faces
throughout the Bering Sea, with the preponderance
of the population in the northern regions (Sowls et al.
1978; Hunt et al., Chapter 40, this volume). Horned
Puffins forage by diving and their foraging efforts ap-
pear restricted during the breeding season to the
vicinity of the islands where they nest (Hunt et al.,
Chapter 39, this volume).
Table 38-11 presents a summary of foods used by
Homed Puffins at the Pribilof Islands in 1975-78.
Fish were the principal food taken, with shallow-
water subtidal forms predominating. In addition, a
modest use was made of a variety of invertebrates.
Preble and McAtee (1923) reported isopods in a
single stomach collected.
Swartz (1966) provided data on eight full stomachs
of Homed Puffins collected at Cape Thompson. Fish
were found in six of the stomachs and invertebrates
in five. Of the fish, gadids were most common, and
polychaetes dominated the invertebrates. Given the
small sample size, it is difficult to judge the signifi-
cance of these data, but Horned Puffin diets at Cape
Thompson appear less dominated by inshore, subtidal
forms than in the Pribilofs.
Tufted Puffin (Lunda cirrhata)
The Tufted Puffin nests in soil burrows throughout
the Bering Sea wherever it can obtain sites free from
disturbance by foxes (Sowls et al. 1978; Hunt et al..
Chapter 40, this volume). Its populations are greater
in the southem Bering Sea than the north. The Tuft-
ed Puffin obtains its food by diving, and its pelagic
distribution indicates that it is primarily an offshore
feeder (Hunt et al.. Chapter 39, this volume).
The diets of Tufted Puffins in the Pribilof Islands
from 1975-78 are summarized in Table 38-11. Fish
made up the major portion of the diet, walleye pol-
lock representing close to one-half of the fish taken.
Inshore subtidal species, predominant in the diet of
Homed Puffins, were absent from the diet of Tufted
Puffins. Nereid polychaete worms made up a signifi-
cant portion of the diet of Tufted Puffins. There are
very few comparative data on Tufted Puffin food
preferences in the Bering Sea region, although Sang-
er (U.S. Fish and Wildlife Service, unpublished data)
supports the contention that gadids, particularly wall-
eye pollock, are important and nereid worms and
sand lance are also used in the southem Bering Sea.
Preble and McAtee (1923) provided no data, and
Swartz (1966) examined only two stomachs at Cape
640 Marine birds
TABLE 38-11
Foods of Tufted and Horned Puffins
Pribilof Islands, 1975-78
Tufted Puffin N = 23
Horned Puffin N = 39
% occurrence
% volume
9?^ number
Species
TP HP
TP HP
TP HP
Nereidae
Cephalopoda
All amphipods
Parathemisto libellula
All fish
Ammodytes hexapterus
Hexagrammos stelleri
Mallotus villosus
Theragra chalcogramma
Trichodon trichodon
26.1
25.6
8.7
10.3
21.7
7.7
8.7
5.1
78.3
89.7
0.0
15.4
0.0
20.5
4.3
2.6
60.9
30.8
0.0
10.3
11.9
3.9
28.7
27.6
1.7
0.7
0.7
0.7
3.4
11.1
4.7
18.8
1.7
11.1
4.5
18.7
79.7
81.4
63.1
52.8
0.0
15.7
0.0
1.3
0.0
24.2
0.0
3.0
5.1
6.5
0.2
0.9
40.7
8.5
45.9
25.9
0.0
8.5
0.0
3.2
Thompson;
pteropod.
both contained fish and one contained a
DISCUSSION
How members of a community partition resources
is a problem of considerable interest to community
ecologists. Several studies of seabirds have addressed
this question, notably the work of Lack (1945) on
cormorants, Ingolfsson (1967) on gulls, Bedard
(1969a and b, 1976) on small auklets, and for inter-
specific relations of whole assemblages, Uspenski
(1958) and Belopolskii (1957) in the Barents Sea,
Swartz (1966) in the Chukchi Sea, Ashmole and
Ashmole (1967) and Ashmole (1968) in the tropi-
cal Pacific, Pearson (1968) in the North Sea, and
Cody (1973) in the eastern North Pacific and North
Atlantic. A number of other authors have provided
valuable data on the trophic relations of various
seabirds. Much of the information of relevance to
the marine birds of the Bering Sea is summarized in
Ainley and Sanger (1979).
In the present review of work on seabird foods in
the Bering Sea, it is obvious that in spite of a resource
base limited in diversity and dominated by a few very
common species, each species of marine bird has a
unique suite of prey species upon which it depends
(Table 38-12). Even though prey species taken over-
lap extensively, the proportions of the different kinds
of prey taken vary from one predator to another.
Within groups of closely related birds (shearwaters,
kittiwakes, murres, auklets, and puffins), the differ-
ences in prey taken by the predators may be particu-
larly important (Tables 38-3, 38-7, 38-10, 38-11).
Differences in prey types are further reinforced by
the selection of prey from different size-classes
(Bedard 1969a, Sanger and Baird 1977a).
Seabirds also partition food resources by foraging
in different regions of the ocean (Hunt et al.. Chapter
39, this volume), or at different distances from their
colonies (Ashmole and Ashmole 1967, Pearson 1968,
Cody 1973), or at different depths (Bedard 1969a,b).
While Bedard (1976) correctly pointed out that in
many instances similair species may forage in mixed
species flocks, data from the Bering Sea (Hunt et al.
1980) suggest that there are considerable differences
in the distances which various species travel in search
of food.
Although some species of marine birds appear rela-
tively specialized in their preferences for natural
foods (shearwaters. Red-legged Kittiwake, Common
Murre, Crested Auklet, Least Auklet, and Tufted Puf-
fin), others seem more generalized (Red-faced Cor-
morant, Black-legged Kittiwake, Thick-billed Murre,
Parakeet Auklet, and Horned Puffin). These differ-
ences in the degree of specialization, particularly
when coupled with differences in foraging grounds
chosen, will also reduce competition. However, de-
spite these preferences for certain kinds or size-classes
of food, most marine birds appear to be opportunistic
Fccdiiifi ecology of sccihirds 04 1
TABLE 38-12
Summary, by food class, of foods used by seabirds, Pribilof Islands, 1975-78
Percent
volume
Sample
Cephalo-
Poly-
Euphau-
size
pods
chaetes
0.0
Copepods
0.0
Amphipods
0.0
siids
3.0
Decapods
0.0
Fish
Northern Fulmar
10
21.2
72.7
Red-faced Cormorant
169
0.0
0.1
0.0
0.4
0.1
14.8
84.3
Black-legged Kittiwake
605
1.0
0.0
0.3
2.9
4.6
0.2
89.3
Red-legged Kittiwake
376
1.9
0.1
0.0
1.2
0.5
0.5
95.5
Common Murre
117
1.2
0.0
0.0
1.5
2.1
0.1
95.2
Thick-billed Murre
233
5.3
0.1
0.0
10.4
6.7
0.5
76.0
Horned Puffin
39
0.7
3.9
0.0
11.1
0.0
0.0
81.4
Tufted Puffin
23
1.7
11.9
0.0
3.4
0.0
0.0
79.7
Parakeet Auklet
55
0.4
23.5
4.1
12.2
10.1
0.0
26.6
Crested Auklet
20
0.0
0.0
0.0
29.6
33.4
0.0
0.8
Least Auklet
258
0.0
0.0
73.5
15.1
0.0
1.2
0.7
in taking advantage of temporarily abundant re-
sources.
One source of evidence for the opportunistic na-
ture of most seabird foraging is the comparison of
temporal and geographic variation in diets. As an ex-
ample of monthly variation, the data presented above
for the two kittiwakes and the Thick-billed Murre
show that diet can change from one month to the
next. Bedard (1969b) and Belopolskii (1957) showed
similar striking changes in the foods taken by seabirds
from the beginning of the breeding season until the
end. While some of this variation in diet may be the
result of changing nutritional needs as the birds go
from courtship to egg production, incubation, and
chick rearing, a large part of the variation is likely to
be accounted for by seasonal changes in the availa-
bility of prey organisms. Only for species in which
the adults forage on small prey items for themselves,
but bring single large items as bill-loads for chicks
(e.g., Thick-billed Murre) is a seasonal change in diet
required.
Relatively few studies of seabird foods have cov-
ered long enough periods v\dth adequate seasonal and
yearly sampling to show annual variation in food use.
Searing's (1977) study of food habits of auklets on
St. Lawrence Island ten years after Bedard (1969a)
completed his research provides such an opportunity.
When these studies are compared, it is clear that while
the size-classes and types of food used were generally
similar, there were also some striking differences in
the prey taxa found by the two studies (Searing
1977). Hunt and Butler (in press), in a study of the
Western Gull (Lams occidentalis) in southern Cali-
fornia, have also found significant annual changes in
the proportion of different kinds of prey taken.
There has been considerable year-to-year variation
in the foods taken at the Pribilofs (Hunt et al. in
preparation). There was also synchrony among bird
species in the years they would increase or decrease
their use of a particular prey. Thus, a peak year for
use of myctophids occurred in 1977 for both of the
kittiwakes and the Thick-billed Murre. Likewise, the
heaviest use of euphausiids occurred in 1978 for both
species of kittiwakes and both murres, and represen-
ted close to a tenfold increase over previous years.
For other foods, either both kittiwakes or both
murres would show a peak of use in the same year.
Changes in dietary habits of this sort, in which
several predatory species vary in tandem, suggest
fluctuations in the availability of specific prey items,
rather than changes in food preferences or require-
ments.
Fluctuations in the availability of specific prey spe-
cies can affect reproductive success and the general-
ized foraging habits of the birds. In California, fluc-
tuations in the availability of fish, the northern an-
chovy (Engraulis mordax) in particular, correlate not
only with the number of gulls attempting to nest, but
also with the gi'owth rates and survival of chicks
(Hunt and Butler in press).
At the Pribilofs, a preliminary analysis of food hab-
its and reproductive success showed that in 1978,
when kittiwake reproduction dropped precipitously
(Hunt et al., Chapter 40, this volume), an unusually
642 Marine birds
high proportion of euphausiids and other inverte-
brates was used by both species of kittiwakes. Belo-
polskii (1957) has mentioned that invertebrates may
be less valuable energetically than fish for raising
young. When adults were forced to use invertebrates
rather than fish, fewer kittiwakes nested and those
that did had lowered reproductive success. A similar
phenomenon may have occurred in the Pribilofs.
The geographic variation in diets probably reflects
the ability of the birds to switch to the most available
food resources. However, most of these changes are
substitutions for organisms of similar form or ecol-
ogy, or changes in the relative abundance of a particu-
lar prey item in the diet. For example, sand lance are
taken in the northern Bering Sea/Norton Sound area
more frequently than in the Pribilofs, and in the
north, Arctic cod are substituted for the walleye pol-
lock used in the southeastern Bering Sea.
Although the monthly, yearly, and geographic vari-
ations in seabird diets suggest that birds may be able
to substitute one food for another readily should a
preferred food become unavailable, it is not clear that
such substitutions can be made on a local level with-
out adverse consequences. For substitutions to work,
there must be an alternative food of equivalent nutri-
tion and availability. If an alternate prey is equally
available and nutritious, it is probably included in the
diet already, and its population may not be able to
support increased use caused by the decrease in an-
other prey species. An alternate prey of equal nutri-
tional value may be available but not as easily taken
because of its distribution. Conversely, an equally
available food source may not have an equivalent nu-
tritional value. Thus substitutions are probably cost-
ly to the birds.
When we examine the foods used by the various
species of birds, it becomes strikingly clear that in
any one area, if not for the Bering Sea as a whole, a
very few kinds of food form the major portion of the
diets of seabirds. For example, in the Pribilofs all
species of birds except auklets contained at least 70
percent fish in their diets with some using up to 99
percent fish (Table 38-12). Of the kinds of fish used,
walleye pollock was by far the most important for all
fish-eating species, with the exception of the Red-
legged Kittiwake and the inshore feeding Red-faced
Cormorant (Tables 38-1, 38-2, 38-3, 38-7, 38-10, 38-
11). In contrast, at Cape Thompson, sand lance and
Arctic cod were the principal forage fish of kittiwakes
and murres (Swartz 1966). Likevdse, in the Barents
Sea colonies studied by Belopolskii (1957), most of
the fish in the birds' diets consisted of sand lance, cod
and herring (Clupea harengus). Thus, with the major
colonies of seabirds dependent upon one or two kinds
of fish, it is very possible that the fate of these colo-
nies may hinge on the population dynamics of these
few prey organisms. The annual changes in types of
foods used with concomitant changes in reproductive
success seen in the Pribilofs, the Barents Sea (Belopol-
skii 1957), and southern California (Hunt and Butler
in press), may be manifestations of this phenomenon.
If a few species of forage fish provide the primary
support for the seabird colonies of the Bering Sea, it
is of interest to know the potential impact of seabirds
on their prey. To provide estimates of the amounts
of prey taken by seabirds we need to know several
facts: the number of birds present, the length of time
they are resident in the Bering Sea, the amount of
food consumed per day per bird, and the proportion
of the various kinds of foods in their diets. The num-
ber of birds present, at least in late spring, summer,
and early fall, can be estimated with reasonable accu-
racy. However, our data on seasonal residency, es-
pecially in vdnter, the amount of food taken per day,
and the proportion of various foods used— except for
the Pribilofs in the breeding season— are only approx-
imations. Given all of these caveats, in Table 39-13
we calculate the approximate yearly food consump-
tion of each seabird species in the eastern Bering Sea.
The total grams of food consumed per year multi-
plied by the estimated percentage of different foods
taken (Table 39-14) based on all available data gives
Table 39-15, the estimated yearly consumption of
each prey type.
Based on the above tables and assumptions, a con-
servative estimate of the consumption by seabirds per
year in eastern Bering Sea shelf waters is 5.8-11.5 X
10^ mt of food. The consumption of 1.5 X 10^ mt
of walleye pollock is equal to about 25 percent of the
catch of the commercial fisheries. Other fish, some
of which are pollock and some unidentified, provide
1.7 X 10^ mt of food to seabirds, followed by 0.8 X
10^ mt of amphipods, primarily Parathemisto libel-
lula, 0.8 X 10^ mt of euphausiids, and 0.7 X 10^ mt
of squids. While all these figures require extensive re-
finement, they do demonstrate that birds consume
large amounts of prey. This consumption of prey
may have its greatest impact in the immediate vicinity
of very large colonies where enormous numbers of
birds forage in relatively restricted areas. In these cal-
culations three species of birds. Short-tailed Shear-
water, Common Murre, and Thick-billed Murre, be-
cause of the size of their populations, are the primary
determinants of the impact of seabirds on the Bering
Sea ecosystem (Tables 38-13, 38-15).
Fluctuations in the availability of prey would af-
fect most drastically the bird species that tend to
specialize, but it is not known how costly it is to a
Feedinfi ccolofiy ofscahirds 643
TABLE 38-13
Estimated yearly consumption of food by selected seabirds of the eastern Bering Sea shelf
Estimated
Bering Sea
Residence
mt*'
mf
Species
Weight
(g)
population^
in days^
of food/yr
of food/yr
Northern Fulmar
620''
2.1X10"
180
2.3X10^
4.7X10"
Short-tailed Shearwater
700^
13.5X10"
120
11.3X10''
22.6X10"
Sooty Shearwater
790^
1.5X10"
120
1.4 XIO^
2.8X10"
Fork-tailed Storm-Petrel
50^
4.0X10"
270
0.5 XIO""
1.0X10"
Red-faced Cormorant
1900*^
1.3X10^
360
0.9X10^
1.8X10"
Black-legged Kittiwake
450^^
2.5X10"
210
2.3X10^
4.7X10"
Red-legged Kittiwake
375^
2.5X10^
240
0.1X10''
0.2X10"
Common Murre
980^*
4.2X10"
300
12.3X10^
24.7 XIO"
Thick-billed Murre
1080*^
4.9X10"
330
17.5X10^
34.9X10"
Parakeet Auklet
290*^
5.3X10^
300
0.5X10^
0.9X10"
Crested Auklet
275*»
1.2X10"
300
1.0X10^
2.0X10"
Least Auklet
100*^
4.5X10"
300
1.3X10^
2.7X10"
Horned Puffin
560*^
3.5X10^
210
0.4X10^
0.8X10"
Tufted Puffin
780^*
1.7X10"
210
2.8X10"
5.6X10"
Total
52.7 XIO"
54.6X10"
109.4X10"
^Residence times and numbers of Fulmars
, Short-tailed
and Sooty Shearwaters, Fork-tailed Storm-Petrels, and Blac
k-legged
Kittiwakes based on Hur
it et al
(Chapter 39, this volume); numbers of o
ther species basec
on Sowls et al. (1978).
•^Calculated on the basis
of a consumption
of 20 percent of the body weight daily X the n
umber
of bird-days in the Bering Sea.
This is a conservative estimate since no all(
awance is made for reproducti
ve effort.
'^Calculated on the basis
of a consumption
of 40 percent
- of the body we
ight daily X the n
umber
of bird-days in the
Bering Sea.
^Hatch 1979.
''Sanger and Baird 1977b.
fPalmer 1962.
^Guess.
'^Hunt et al. in preparation.
generalist to have to substitute one species of prey for
another. The geographic, seasonal, and year-to-year
variations in diets can sometimes be correlated w^ith
prey availability, which may be affected by oceano-
graphic conditions. Weather has been shown to play
an important part in the survival rate as well as dis-
persal of walleye pollock (Walsh and McRoy 1978)
and northern anchovies (Lasker in press), and it may
also affect the foraging capabilities of some species
(Hunt et al.. Chapter 40, this volume). Thus, not
only do birds and their prey influence each other's
dynamics, but the effects of weather and other physi-
cal factors are superimposed on the system as a
whole.
ACKNOWLEDGMENTS
We thank Albert Adams, Gary Brusca, Doug Siegel-
Causey, Robert Cimberg, Ted Cooney, Christian Fau-
chald, John Fitch, Abe Fleminger, Kathy Frost,
Elizabeth Hall, Eric Hochberg, Kuni Hulsemann, Bar-
bara Mayer, George Mueller, Jay Quast, Mary Wick-
sten, Richard Winn, and Robert Wolotira, Jr., for
their help in species identifications; National Marine
Fisheries Service, St. Paul Island, for their logistic
support; Molly Warner for setting up the studies on
the Pribilof Islands; field assistants B. Braun, Z.
Eppley, B. Mayer, M. Naughton, B. Rodstrom, D.
Siegel-Causey, R. Squibb, and D. Swartz; Grace Bush,
TABLE 38-14
Estimated partitioning of diets of selected Bering Sea seabirds by major food categories.
Percent by
weight'
Species
Euphausiids
Amphipods
Cephalopods
Pollock
Other fish
Northern Fulmar
5
5
25
55
10
Short-tailed Shearwater
30
30
30
10
Sooty Shearwater
10
40
40
Fork-tailed Storm-Petrel
30
30
30
Red-faced Cormorant
5
75
Black-legged Kittiwake
15
15
25
45
Red-legged Kittiwake
10
5
10
20
55
Common Murre
5
15
35
45
Thick-billed Murre
15
10
10
35
30
Parakeet Auklet
30
30
5
20
Crested Auklet
50
25
Least Auklet
5
5
Horned Puffin
10
10
70
Tufted Puffin
5
5
40
45
Values adjusted for best-guess estimate of yearly diet for whole eastern shelf region.
TABLE 38-15
Estimated yearly consumption of major food types by selected sea birds on the waters of the
eastern Bering Sea shelf, based on estimates in Tables 38-13 and 38-14,
assuming a consumption of 20 percent of a bird's body weight per day.
Yearly consumption in mt x 10''
Species
Euphausiids
Amphipods
Cephalopods
Pollock
Other fish
Northern Fulmar
Short-tailed Shearwater
Sooty Shearwater
Fork-tailed Storm-Petrel
Red-faced Cormorant
Black-legged Kittiwake
Red-legged Kittiwake
Common Murre
Thick-billed Murre
Parakeet Auklet
Crested Auklet
Least Auklet
Horned Puffin
Tufted Puffin
Total
0.1
3.4
0.1
0.1
0.3
0.0
0.6
2.6
0.0
0.5
0.0
7.7
0.1
3.4
0.3
0.0
1.9
1.7
0.0
0.3
0.1
0.1
0.1
8.0
0.6
3.4
0.5
0.1
0.0
1.7
0.1
6.4
1.3
0.1
0.6
0.0
4.3
6.1
0.0
0.1
1.1
13.6
0.2
1.1
0.5
0.1
0.7
1.0
0.1
5.5
5.3
0.0
0.3
1.3
16.1
644
Feeding ecology of seabirds 645
I
Zoe Eppley, Jim Mershman, and Carolyn Wallace for
their assistance in getting the data into the computer;
Hal Peterson's Data Project Group at the University
of Rhode Island for the computer analysis and
output; Lucia Schnebelt and Tana Forstrom for their
patience and understanding while typing numerous
drafts of this chapter; and Nancy Smiley for the
illustration. Without the cooperation of all of these
people, this study would not have been possible.
This study was supported by the Bureau of Land
Management through interagency agreement with the
National Oceanographic and Atmospheric Adminis-
tration, under which a multiyear program responding
to needs of petroleum development of the Alaskan
continental shelf is managed by the Outer Continen-
tal Shelf Environmental Assessment Program
(OCSEAP) Office.
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Breeding and population ecology of
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1945
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1974 Plankton of the Bering Sea. In:
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1977
Some aspects of the ecology of cliff-
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1978 Catalog of Alaskan seabird colonies.
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1972
Preliminary standing stock and bio-
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Spring, L.
1971
A comparison of functional and mor-
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billed Murre (Uria lomuia). Condor
73: 1-27.
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1977a The trophic relationships of marine
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Southern Bering Sea. In: Environ-
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Rep. 4:694-757.
Swartz, L. G.
1966
Sea-cliff birds. In: Environment of
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N. J. Wilimovsky and J. N. Wolfe,
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1977b Ecosystem dynamics birds and marine
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Alaskan continental shelf. NOAA/
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12:372-417.
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1960
The murres. Their distribution, pop-
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Sanger, G. A.,
1978
Sealy, S. G.
1973
V. F. Hironaka, and A. K. Fukuyama
The feeding ecology and trophic rela-
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3:773-848.
Interspecific feeding assemblages of
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Auk 90: 796-802.
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1958 The bird bazaars of Novaya Zemlya.
(Transl. from Russian) Transl. Dep.
Northern Aff. Nat. Res., Canada.
Walsh, J. J., and C. P. McRoy
1978 Ecosystem analysis and synthesis in
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Prog. Rep. on Processes and Resources
of the Bering Sea shelf (PROBES),
Proc. Rep., 386-403. Inst. Mar. Sci.,
Univ. Alaska, Fairbanks.
Breeding Distribution
and Reproductive Biology of Marine Birds
in the Eastern Bering Sea
George L. Hunt, Jr.,' Zoe Eppley," and
William H. Drury'
'Department of Ecology and Evolutionary Biology
University of California, Irvine
^College of the Atlantic
Bar Harbor, Maine
ABSTRACT
In this chapter, we synthesize recent work on the reproduc-
tive biology and breeding distribution of marine birds nesting
on the coasts and islands of the eastern Bering Sea from the
Bering Strait to the eastern Aleutian Islands. Most breeding
birds are concentrated in a few very large colonies. The distri-
bution of many cliff-nesting species appears to be limited by
habitat, while some other species may be limited by the
distribution of preferred prey. There are major differences
in the stability of reproductive success between species and be-
tween colonies. These differences reflect the dependability
and diversity of prey populations near the colonies and the dif-
fering prey-capture abilities of seabird species. The alcids
predominate throughout the Bering Sea and have relatively
stable levels of productivity. In contrast to these divers, the
reproductive success of kittiwakes shows greater yearly fluctu-
ations, particularly in regions where these birds are dependent
upon variable fish populations.
INTRODUCTION
This chapter reviews and brings up to date the
knowledge of the distribution, numbers, and repro-
ductive biology of marine birds breeding in the east-
em Bering Sea. We examine the impact of availability
of prey and of nesting habitat on the distribution and
numbers of breeding seabirds. We relate the constan-
cy of reproductive success to foraging strategies and
the biology of prey species. The additional problem
of the relationship between foraging strategy and the
colony size and dispersal of individual species (Lack
1967, 1968; Cody 1973) will be addressed in a future
paper.
Before 1973, information available on seabirds
breeding in the Bering Sea was derived from short
visits to colonies, and consisted of narrative informa-
tion, brief species accounts, and population estimates.
Only the northern auklets had received extensive
study (Bedard 1967, 1969b and c; Sealy 1968;Sealy
and Bedard 1973). Information on cliff -nesting spe-
cies was more limited. Swartz (1966) conducted a
major study at Cape Thompson in the Chukchi Sea,
Dick and Dick (1971) provided considerable informa-
tion on seabirds breeding at Cape Peirce, and Fay and
Cade (1959) reported on the colonies of St. Lawrence
Island.
Since 1975, the Bureau of Land Management/
National Oceanic and Atmospheric Administration
Outer Continental Shelf Environmental Assessment
Program (OCSEAP) has sponsored studies on the
breeding biology of seabirds in the southeastern Be-
ring Sea at the Pribilof Islands and Cape Peirce, in the
northeastern Bering Sea at St. Lawrence, Little Dio-
mede. King, and Sledge islands, and at numerous sites
in Norton Sound. Many short reconnaissance trips
have been made to establish or verify numbers of sea-
birds at other colonies in Alaska.
Using the Catalog of Alaskan Seabird Colonies
(Sowls et al. 1978) as a baseline and with additional
updates, we give the distribution and numbers of all
common species of seabirds breeding in the eastern
Bering Sea. Discussions of breeding biology are
based primarily on unpublished data originating in
OCSEAP-sponsored studies. In order to put these
649
650 Marine birds
data on reproductive biology in the Bering Sea into
broader perspective, we have drawn comparisons with
information from elsewhere in Alaska or the North
Atlantic, when appropriate data are available. Species
are treated in taxonomic order. A few species that
are relatively uncommon or for which no information
is available are not treated in this chapter. These in-
clude: murrelets (Brachyramphus sp., Synthlibo-
ramphus), southern auklets (Cerorhinca monocerata,
Pty choramphus aleuticus), Brandt's Cormorant (Phala-
crocorax penicillatus). Black Guillemot (Cepphus
grylle), and Herring (Larus argentatus) and Mew Gulls
(L. canus).
This chapter deals with seabirds that breed in colo-
nies from Yanuska Island in the Aleutian Islands
north to the Bering Strait, excluding the south side
of the Alaska Peninsula. The Aleutian Islands are
largely outside the scope of this chapter. These is-
lands are of major importance for seabirds (Sekora et
al. 1979), but information on numbers and breeding
biology of species is incomplete.
PROCELLARIIDAE
Species in the family Procellariidae are surface-
feeders or pursuit-plungers, using only the upper por-
tion of the water column for feeding (Ashmole 1971,
Ainley and Sanger 1979). The Procellariids range far-
ther from their colonies to obtain food than the
diving birds. Long flight ranges and slow chick
growth rates have evolved in this family as adapta-
tions to patchily distributed food (Boersma and
Wheelwright 1979). The center of distribution is in
the southern hemisphere; the Northern Fulmar is the
only representative of the family breeding in the Be-
ring Sea. Short-tailed (Puffinus tenuirostris) and
Sooty Shearwaters (P. griseus), which breed on is-
lands off Australia, New Zealand, and South America,
spend the austral winter foraging over the Bering Sea.
The biomass of the shearwaters in the Bering Sea
during the northern summer warrants their considera-
tion as the most important seabird species in the
area (Sanger and Baird 1977).
Northern Fulmar (Fulmarus glacialis)
Distribution
Northern Fulmars breed throughout the northern
Atlantic. In the Pacific, they breed in the Bering Sea,
in the Gulf of Alaska, and on the Kurile, Komandor-
sky, and Aleutian islands. Both the Pacific and
Atlantic populations extend into the Arctic Ocean.
Light and dark color phases occur in both popula-
tions. In the Bering Sea, the light phase predominates
in the north, the dark phase in the south.
Habitat
Fulmars nest on cliffs and breed in association with
other cliff-nesting species, such as murres and kitti-
wakes. On fox-free islands, fulmars generally nest on
the upper, vegetated portions of the cliffs. On islands
with mammalian predators, fulmars lay their eggs in
cavelets or on bedrock ledges on the nearly vertical
portions of the cliffs.
Colonies
The entire breeding population of the Pacific ful-
mar is concentrated in a few colonies; 1.5 million ful-
mars breed at 12 more or less distinct colonies in
Alaska. The major colonies include St. Matthew and
St. George in the Bering Sea, Chagulak in the western
Aleutians, and the Semidi Islands in the Gulf of Alas-
ka (Sowls et al. 1978). Bering Sea colonies range
from 400 to 450,000 birds (Fig. 39-1).
Status of the Bering Sea population
The fulmar population in the eastern Bering Sea is
estimated at 1.3 million (Sowls et al. 1978). The
fulmar population is known to be expanding in the
Atlantic; the status of the Bering Sea population is
unknown.
Reproductive biology
The breeding biology of the Atlantic population
has been studied extensively (Fisher 1952; Carrick
and Dunnet 1954; Dunnet and OUason 1978a, b;
Ollason and Dunnet 1978; Dunnet et al. 1979). The
Pacific race has been studied in the Gulf of Alaska on
170 175 180
170 165 t60* 155' 150"*
■^■%....
^
^^^
./ *-^--=:>$.
NORTHERN FULMAR
Colony Size
. 1-100 birds
• 101- 1,000 b.fds
• 1001- 10,000 birds
W 10,001- 100.000 buds
^100.001 1,000,000 birds
' Unknown number of birds
Figure 39-1. Northern Fulmar colonies in the Bering Sea.
Breeding dislrihuliun and reproductive biology 651
the Semidi Islands (Hatch 1977, 1978, 1979) and in
the Bering Sea on the Pribilof Islands (Hunt et al. in
preparation).
Fulmars lay a single egg and incubate it for an av-
erage of 47-48 days (range, 46-51 days) (Hatch
1979). Temporary desertion of eggs, apparently due
to lack of available food, was a common occurrence
in the Semidi population of fulmars in 1976 (Hatch
1977). The fact that egg neglect has not been ob-
served in the Pribilof population may indicate a bet-
ter food situation. Young fulmars remain at the nest
site for a mean of 53 days (range 49-58) (Mougin
1967, Hatch 1979). Once fledged, the young are in-
dependent.
Table 39-1 compares fulmar reproductive success
within the Bering Sea. A minimum value of repro-
ductive success for population maintenance was esti-
mated to be about 0.16 young fledged per nest (S.A.
Hatch, University of California, Berkeley, personal
communication). By this estimate, fulmars on the
Pribilofs and the Semidi Islands probably produce
more than enough young to maintain their popula-
tions. The figures for the Pribilofs represent a mini-
mum estimate of reproductive output, since an un-
known number of adults were undoubtedly non-
breeding birds.
TABLE 39-1
Northern Fulmar reproductive success
1976 1977 1978
units
inhabit oceans from Antarctica north to the Aleutian
Islands. Two species are known to breed in the Gulf
of Alaska: the Fork-tailed Storm -Petrel (Oceano-
droma f areata) and Leach's Storm-Petrel (O. leuco-
rhoa). The northern limit of the known breeding
range for this family in the Pacific is the Aleutian Is-
lands; as yet there is no evidence that storm-petrels
breed in the Bering Sea. Hydrobatids, like the
procellariids, are characterized by foraging long
distances from their colonies, and by long incubation
and nestling periods. It is not known why storm-
petrels do not breed in the Bering Sea; Boersma and
WheelwTight (1979) speculate that short nights at
high latitudes and the frequent occurrence of storms
may restrict their foraging and ability to visit their
colonies.
PHALACROCORACIDAE
Three species of this family of diving seabirds
breed in the Bering Sea: Pelagic, Double-crested, and
Red-faced Cormorants (Fig. 39-2). The Red-faced
Cormorant is the most numerous and is endemic to
the Bering Sea and Gulf of Alaska. The Pelagic Cor-
morant has the wddest and most northerly distribu-
tion, reaching into the Chukchi Sea and south to the
Channel Islands of California. Double-crested Cor-
morants in the eastern Bering Sea are confined to
Bristol Bay. Red-faced Cormorants are restricted to
the more southern region of the Bering Sea. Cormo-
rants make up a small portion of large, multispecies
colonies. They are numerous in coastal waters and
bays and are rarely seen more than a few kilometers
Semidi Islands 0.15 0.51
chicks fledged/egg
(Hatch 1977,1978)
Pribilof Islands
St. Paul
0.15 0.30 0.27 chicks fledged/mean
no. adults in study
area (Hunt et al.
1978)
St. George Island
0.34 0.29 chicks fledged/mean
no. adults in study
area (Hunt et al.
1978)
HYDROBATIDAE
The hydrobatids or storm-petrels are small, pelagic
seabirds that feed on small crustaceans or zooplank-
ton at the water's surface (Sowls et al. 1978). They
/
Tt
: : /;:
• i
«
•
•
T
T
T
5»
PHALACROCORAX SPP
- ^isS
Colony Size
^S^ ;,
• 1-100 bifds
^:'-'
• 101- 1,000 bifds
• 1001-10.000 b.rds
9 10,001-100.000 birds
^100.001-1,000,000 birds
.#r
•T
^ Unknown number or birds
m.^
T
Figure 39-2. Cormorant colonies in the Bering Sea.
652 Marine birds
from land. Unlike the Procellariidae and Alcidae,
they lay several eggs and have a correspondingly high
reproductive potential.
Double-crested Cormorant (Phalacrocorax auritus)
Distribution
The Double-crested Cormorant breeds from the
southwestern Bering Sea, central Canada, and New-
foundland south to Mexico and the Bahamas
(Godfrey 1966, Palmer 1962). In Alaska, these cor-
morants are most numerous in the western Gulf of
Alaska and in Bristol Bay. In the Bering Sea, Cape
Newenham is the northern limit of their breeding
range (Sowls et al. 1978). They are thought to leave
the Bering Sea during the winter and move south to-
ward British Columbia (Gabrielson and Lincoln
1959).
Habitat
Double-crested Cormorants nest on cliffs, flat
islands, and gradual slopes, in trees, and on islands in
freshwater lakes (Godfrey 1966). Sowls et al. (1978)
report minor use of freshwater habitats in Alaska.
Colonies
In the Bering Sea, Double-crested Cormorant colo-
nies are small, ranging in size up to 800 birds. Infor-
mation on cormorant colonies is not detailed, since
censuses have not consistently distinguished among
cormorant species. Double-crested Cormorants occur
in the smallest numbers and their colonies are the
smallest among Bering Sea cormorants (Fig. 39-3)
(Sekora et al. 1979).
Status of the Bering Sea population
The Bering Sea population is estimated to number
under 3,000 (Sowls et al. 1978); the status of the
population is unknown.
Reproductive biology
No major studies have been done in the Bering Sea,
but the reproductive biology of Double-crested Cor-
morants south of the region is well known. Van Tets
(1959), working on Mandarte Island in British Colum-
bia, found that clutches of three to five eggs were laid
in late May or early June; this is also true at Cape
Peirce in the Bering Sea (M. Dick, Alaska Department
of Fish and Game, personal communication). The in-
cubation period for the species averages about 28
days. Chicks start flying at five to six weeks of age
and leave the next one to two weeks later (Drent et
al. 1964). Reproductive success averaged 2.4 young
170° 175* 180*
175
m'
165-
i6or
155'
150
n
ill
' • ' "f^ —
iik .:
65'
^Svi
ill
;
-m;.
'ma
%
— ^^—^
-
:---.::..::.:.;,/ A
^^^'%«
t
_3
J
piP'S:"" "**■ -
62^
%
'i
ssr
-
• f
'^:' k
56
DOUBLE-CRESTED CORMORANT
, ^
Colony S\ze
. 1-100 birds
* 101-1,000 bi'ds
• 1001-10.000 birds
W 10,001-100,000 birds
^100,001-1,000,000 birds
53"
▼ Unknown number o! birds
1
Figure 39-3. Double-crested Cormorant colonies in the
Bering Sea.
fledged per nest during the two-year study (van Tets
1959). Tavemer (1915) and Lewis (1929) provide
basic information on the breeding biology of this spe-
cies in the western Atlantic.
Pelagic Cormorant (Phalacrocorax pelagicus)
Distribution
Pelagic Cormorants breed from northeastern Sibe-
ria to Japan and southern China, and from the Bering
and Chukchi seas in Alaska (Godfrey 1966) to the
Channel Islands in California (Dick 1975, Hunt et al.
in press).
Habitat
Pelagic Cormorants usually nest on small ledges on
precipitous sea cliffs (Drent et al. 1964).
Colonies
Pelagic Cormorants occur in small colonies dis-
persed throughout the Bering Sea (Fig. 39-4). Most
colonies number less than 100, but a few number
into the thousands. The largest colony occurs near
Cape Newenham on the Walrus Islands. Throughout
the Bering Sea, they frequently nest in association
with large numbers of Black-legged Kittiwakes, with
which they compete for nest sites (Dick and Dick
1971).
Status of the Bering Sea population
The Bering Sea population of Pelagic Cormorants is
Brccdinfi distribution and reproductive hioloffy 653
170"
is-~iii
175'
\m 166
160- ISS 1-
jpiiii
ii;;. ■,,;.,,.„
-■- ■: —
i'.:: '
II|II
.«li
**• *
1 ,
^4
m •
T.
PELAGIC CORMORANT
Colony Si
. 1-100
birds
▼
• 101-1
000 bitds
• 1001-
W 10,001
^100,00
0,000 birds
- 100,000 birds
1-1.000,000 birds
T
▼ Unkno
wn number ot birds
Figure 39-4. Pelagic Cormorant colonies in the Bering Sea.
estimated at about 48,000 (Sowls et al. 1978).
status of this population is unknown.
The
Reproductive biology
The most complete study of Pelagic Cormorants in
the Bering Sea was made by Dick (1975) at Cape
Peirce. Other studies from the Bering Strait
(Biderman and Drury 1978), St. Lawrence Island
(Searing 1977), and Norton Sound (Drury 1976,
Drury and Steele 1977, Biderman et al. 1978) fur-
nished similar information but were less extensive.
Phenology
In the Bering Sea, Pelagic Cormorants arrive at
their southeastern colonies (Cape Peirce) in the
middle of April and by mid- to late May at their
northern colonies (Norton Sound and the Diomedes).
They leave the colonies between the end of Septem-
ber and the beginning of October, and probably win-
ter in the eastern Aleutian Islands (Dick 1975). They
remain at Bluff in Norton Sound until close to the
time of freeze-up (Martin Olson, personal communi-
cation). As soon as the cliffs are fairly free of snow,
nest-building begins. At Cape Peirce, egg-laying be-
gins during the third week of May, with the peak of
laying occurring one to two weeks later. Dick (1975)
reported an average two-day period between the lay-
ing of successive eggs.
It is interesting to note that the breeding events of
Pelagic Cormorants occur one to two weeks earlier at
Cape Peirce than at Mandarte Island, B.C., 10° fur-
ther south. Black-legged Kittiwakes start laying at
Cape Peirce in early June, and early nesting by the
cormorants allows them to compete effectively with
kittiwakes for nest sites (Dick 1975).
At Cape Peirce, clutch size ranged from one to five
eggs (Dick 1975); the maximum found at Mandarte
Island was six eggs (Drent et al. 1964). Mean clutch
size at Cape Peirce was 3.1 eggs per nest (Dick 1975),
at Mandarte, 3.8 eggs per nest (Drent et al. 1964),
and at Norton Sound, 3.5 eggs per nest (Biderman et
al. 1978). At least for Cape Peirce and Mandarte,
there are regional differences in clutch size. Cormo-
rants at Mandarte commonly lay again when clutches
are lost; this occurs to a lesser degree at Cape Peirce,
and during 1970, a year with harsh weather, cormo-
rants did not replace lost eggs (Dick 1975).
Once hatched, chicks remain in the nest until they
are capable of flight, a period of about 50 days. Fly-
ing young stay in the vicinity of the nest for a couple
of weeks and continue to be fed by their parents.
Most chicks have fledged by the last week in August
(Dick 1975).
Productivity
Productivity of Pelagic Cormorants is given for two
sites in the Bering Sea and Mandarte Island in British
Columbia (Table 39-2). Colonies in Norton Sound
showed the highest level of reproductive success. Ex-
ceedingly poor weather contributed to the generally
lower success at Cape Peirce by causing wetting of
chicks and interruptions in feeding (Dick 1975). Pre-
dation by gulls has a major impact on cormorant
productivity at Mandarte; predation apparently oc-
curs less frequently at Cape Peirce (Dick 1975).
Data on growrth rates of Pelagic Cormorants nesting
in the Bering Sea are not available. However, Dick
(1975) saw differential rates of growth between older
TABLE 39-2
Estimates of reproductive success of Pelagic Cormorants
(chicks
fledged/nest) year
Bluff, Norton Sound
(Biderman et al. 1978)
2.4
1977
Cape Peirce, Bering Sea
(Dick and Dick 1971,
1.3
1970
Petersen and Sigman 1977)
2.4
1976
Mandarte Island, B.C.
(Dick 1975)
2.0
1958-9
654 Marine birds
and younger chicks at Cape Peirce. Chicks hatched
asynchronously; the slower growth rates of younger
chicks exacerbated size differences, and often the
youngest chick in a brood succumbed to starvation at
an early age.
Red-faced Cormorant (Phalacrocorax urile)
Distribution
The distribution of Red-faced Cormorants is cen-
tered in the Aleutian Islands and extends into the
Gulf of Alaska (Gabrielson and Lincoln 1959). They
breed in the Pribilof and Aleutian islands, along Bris-
tol Bay (Sowls et al. 1978), and on the Siberian coast-
line (Nelson 1883).
Habitat
Red-faced Cormorants nest in scattered pairs or in
small groups among other cliff-nesting species. On
the Pribilof Islands, Red-faced Cormorants prefer to
nest on low areas of cliffs. Like the other cormo-
rants, they may shift the location of their nests and
colonies from year to year.
Colony size
In the Bering Sea, Red-faced Cormorant colonies
are small (Fig. 39-5): most colonies contain between
100 and 1,000 birds.
170~' 175° 180°
175'
170
165 160*
155-
150'
i
1
111
"1
1- -"
•
T
RED-FACED CORMORANT
•
▼
--
Colony Size
. 1- too birds
. •
• lOT- 1,000 birds
• 1001-10,000 birds
• 10,001-100,000 birds
J^^
^100,001-1,000,000 bitds
•
▼ Unknown number ot birds
A*
Figure 39-5. Red-faced Cormorant colonies in the Bering
Sea.
Status of the Bering Sea population
Red-faced Cormorants are the most abundant of
the cormorant species in the Bering Sea. The popula-
tion in the eastern Bering Sea has been estimated at
41,300 (Sowls et al. 1978). The population in the
Gulf of Alaska is expanding (Kessel and Gibson
1978); the status of the Bering Sea population is un-
known.
Reproductive biology
Red-faced Cormorants have been studied in the
Bering Sea, at the Pribilof Islands (Hunt et al. 1978),
and briefly at Cape Peirce (Petersen and Sigman
1977).
Phenology
Red-faced Cormorants are year-round residents at
some of their colonies in the south of their range and
are among the earliest breeders in the seabird com-
munity; on the Pribilof Islands egg-laying commences
in early May. Red-faced Cormorants lay one to
four eggs. The incubation period is about 31 days,
and chicks remain in the nest for around 59 days
(Hunt et al. in preparation).
Productivity
Successful nests on the Pribilofs between 1975 and
1978 consistently fledged two young per nest. Gulls
take large numbers of cormorant eggs and nestlings in
colonies along the Aleutian chain and in Bristol Bay,
but are not a cause of mortality on the Pribilof Is-
lands.
LARIDAE
Eight species of larids nest in the eastern Bering
Sea: Herring, Mew, Glaucous and Glaucous-winged
Gulls, Black- and Red-legged Kittiwakes, and Arctic
and Aleutian Terns. The Herring and Mew Gulls are
few in number vdth limited distributions in the Be-
ring Sea; hence these two species will not be dis-
cussed.
Two types of feeding strategies are exemplified by
members of the Laridae: gulls are scavengers, egg pre-
dators, or coastal foragers; pelagic kittiwakes are
surface-feeders, as are terns, which fish in coastal
waters and estuaries. The kittiwakes are the most
numerous of the larids in the Bering Sea, while the
large gulls comprise only a small percentage of large
seabird colonies. Although the status of Bering Sea
populations of large gulls is unknown, we may expect
populations of these birds to increase as waste food
from man becomes more available with continued
coastal development.
Breeding distribuliun and rcproducliue biolofiy 655
Glaucous Gull (Larus hyperborcus)
Distribution
The breeding range of Glaucous Gulls is circum-
polar in the northern hemisphere. They nest along
the coasts and islands from Bristol Bay north to the
Yukon and Mackenzie rivers (Gabrielson and Lincoln
1959). The southern extent of the breeding range of
this arctic species is generally about 59° N (Sowls et
al. 1978).
Habitat
Glaucous Gulls nest on cliffs among other cliff-
nesting seabirds and on the ground in monospecific
colonies. They forage on refuse from human settle-
ments, as well as on natural prey.
Colonies
Glaucous Gull populations nesting within multi-
specific colonies are small, usually numbering fewer
than 1,000 birds (Fig. 39-6). Glaucous Gulls appear
to replace Glaucous-winged Gulls in the northern Be-
ring Sea. One of the few places where both species
formerly occurred together was on Walrus Island of
the Pribilof group. This colony has since been dis-
placed by Steller sea lions (Eumetopias jubatus), but
it was once in the midst of one of the largest murre
colonies known (Preble and McAtee 1923). Perhaps
this large and predictable supply of food in the form
of murre eggs and chicks allowed the two species of
gull to coexist.
Status of the Bering Sea population
The eastern Bering Sea population of Glaucous
Gulls is estimated at 19,500 (Sowls et al. 1978). The
status of the population is unknown.
Reproductive biology
The phenology of Glaucous Gulls breeding on St.
Lawrence Island has been studied by Searing (1977).
Reproductive success for the populations in Norton
Sound was determined in 1976 and 1977 (Drury and
Steele 1977, Biderman et al. 1978).
Phenology
Glaucous Gulls are the earliest gulls to begin nest-
ing in the northern Bering Sea colonies. They are
year-round residents at St. Lawrence Island (Searing
1977) and St. Matthew Island (McRoy et al. 1971).
At other colonies they are among the earliest to ar-
rive and the latest to leave (Biderman et al. 1978).
On St. Lav^nrence Island, Glaucous Gulls began lay-
ing on 2 June 1976; however, 1976 was generally a
disastrous year for St. Lawrence seabirds and this
phenology may not be representative of a normal
year. Glaucous Gulls in Norton Sound began laying
much earlier, reaching the peak of laying about 7
June in 1977.
Glaucous Gull colonies often show large annual
variations in mean clutch size. In Norton Sound,
mean clutch size in 1976 was 2.8 eggs, similar to that
reported for Cape Thompson in the Chukchi Sea and
for St. Lawrence Island; the next year clutch size av-
eraged only 1.3 eggs in Norton Sound.
Productivity
Although sample sizes were small, Norton Sound
gulls provided us with three years of data on produc-
tivity (Drury and Steele 1977, Biderman et al. 1978).
Glaucous Gulls at these colonies showed very stable
levels of reproductive success, varying between a low
of 0.50 chicks fledged per nest built in 1975 to a high
of 0.67 in 1976 and 0.63 in 1977. In contrast.
Glaucous Gulls nesting at St. Lawrence Island failed
to raise young in 1976.
Glaucous-winged Gull (Larus glaucescens)
Distribution
Glaucous-winged Gulls breed from Nunivak Island
in the Bering Sea south to the state of Washington
and west to the Komandorsky Islands (Gabrielson
and Lincoln 1959).
170 175 160
175
70 165 160
155
150
1
i:=:-^
■ T
▼
^
%, "'
GLAUCOUS GULL
Colony Sue
jii;
. 1-100 b.fds
• 101 1.000 birds
• 1001-10.000 birds
#10,001-100.000 birds
^100,001 1,000.000 birds
-.^^vi;
▼ Unknown number o( birds
Figure 39-6. Glaucous Gull colonies in the Bering Sea.
6.56 Marine birds
Habitat
These birds inhabit coastal areas and islands, nest-
ing on beaches, sandbars, and cliffs, usually near
human settlements or seabird colonies, from which
they obtain food.
Colonies
Glaucous-winged Gulls nest in small colonies of
usually fewer than 1,000 birds (Fig. 39-7). The distri-
bution of the colonies is similar to the distributions
of cormorant, kittiwake, and murre colonies; the eggs
and chicks of these species provide a food source for
the gulls.
Status of the Bering Sea population
The eastern Bering Sea population of Glaucous-
winged Gulls is estimated to be 84,000 (Sowls et al.
1978). Although the status of the Bering Sea popula-
tion has not been determined, the population in the
Gulf of Alaska may be increasing (Baird et al. 1979).
Reproductive biology
The breeding biology of Glaucous-winged Gulls in
British Columbia is well known (Vermeer 1963, Ward
1973, Hunt and Hunt 1976). This species has been
studied in the Gulf of Alaska by several U.S. Fish and
Wildlife Service teams; their findings are summarized
in Baird et al. (1979). Only one study of the Bering
Sea population has been conducted (Petersen and
Sigman 1977).
170- 175" 180"
175 170
165
160 155'
150'
^^^^^^
:::;:i:;i;:;:i:;:S;:::;:^;:g;:;:::|:^; I ,
^
'
w
Vi-
l^*c-
▼
A'
GLAUCOUS-WINGED GULL
▼
••
Colony Siio
. 1 100 bifds
• 101 t, 000 birds
• 1001 10,000 birds
9 inooi-iooooo birds
^1 "1001 1,000.000 birds
▼ Unknown number ot birds
Jr
\
■SSf
/
r^
Figure 39-7. Glaucous-winged Gull colonies in the Bering
Sea.
Phenology
At Mandarte Island in British Columbia, the peak
of laying occurs between late May and early June
(Vermeer 1963, Hunt and Hunt 1976). Similarly, the
peak of laying recorded at Zaimaka Island in the Gulf
of Alaska in 1978 was on 6 June (Nysewander and
Barbour 1979). Phenological data about Glaucous-
winged Gulls nesting at Cape Peirce in the Bering Sea
also agree with those of Vermeer (1963); on 6 June
in 1976, most nests contained at least one egg. At
Mandarte Island, the incubation period lasted an
average of 27 days (Vermeer 1963). At Zaimaka
Island, eggs began to hatch on 25 June, and hatching
continued to 3 July in both 1977 and 1978
(Nysewander and Barbour 1979). Young remain in
the nest about 44 days before making their first
flight (Vermeer 1963). Fledging at Zaimaka in 1977
and 1978 began on 26 July (Nysewander and
Barbour 1979).
At Zaimaka Island, clutch size was 2.64 eggs per
nest-with-eggs in 1977 and 2.49 in 1978 (Nysewander
and Barbour 1979). These values are slightly smaller
than the clutch size of 2.82 found at Mandarte in
1962 (Vermeer 1963). Glaucous-winged Gulls often
lay again when egg loss occurs. At Zaimaka Island,
relaying occurred between 25 and 29 June; these eggs
hatched between 5 and 15 July, substantially later
than original clutches, which hatched between 25
June and 3 July.
Productivity
On Mandarte Island, Glaucous-winged Gulls
fledged 1.0 young per pair which produced eggs (a
measure equivalent to chicks fledged per nest-with-
eggs) in 1961 and 1.7 in 1962 (Vermeer 1963). Zai-
maka Island showed similar variation in productivity,
with 1.39 chicks fledged per nest-with-eggs in 1977
and 0.80 chicks fledged per nest-with-eggs in 1978
(Nysewander and Barbour 1979).
Black-legged Kittiwake (Rissa tridactyla)
Distribution
Black-legged Kittiwakes are circumpolar in distri-
bution, breeding throughout the Arctic Ocean, the
Chukchi and Bering seas, and the North Atlantic and
North Pacific oceans. They breed at lower latitudes
in the North Atlantic than in the Pacific. In the
North Atlantic their southern breeding limits tend to
follow the distribution of arctic waters (sea-surface T
< 10 C) (Coulson 1974). In the Pacific, most of the
kittiwake colonies occur in arctic waters, although
the southern colonies, in the Gulf of Alaska, are in
warmer waters.
Brccdinti (ILslrihulion and rcproductiuc hioluf^y 657
I
Habitat
Kittiwakes nest on small ledges on vertical cliffs
(Coulson 1974). At the Pribilofs they prefer the
lower portions of the cliff-face and are not found
above 180 m (Hunt et al. in preparation). There have
been reports of kittiwakes nesting on gradual slopes
in a predator-free environment in Alaska (Sowls et al.
1978). Where cliffs are scarce in southern England,
kittiwakes nest on window ledges of deserted build-
ings and have attempted nesting on sand dunes
(Coulson 1974).
Colonies
Black-legged Kittiwakes nest in over 50 colonies
in the Bering Sea (Fig. 39-8). Although these colo-
nies range in size from a few pairs to several thou-
sand, most contain between 1,000 and 10,000 birds.
The largest kittiwake colony is at Cape Peirce, and
consists of over 200,000 birds (Sowls et al. 1978).
The distribution of kittiwake colonies in the Bering
Sea is closely linked to the occurrence of cliffs.
Status of the Bering Sea population
There is evidence that the Black-legged Kittiwake
population is increasing on St. Paul Island in the Prib-
ilofs. In 1954, Kenyon and Phillips (1965) counted
Black-legged Kittiwake nests at specific locations
around the island. Hie key and Craighead (1977) re-
peated these counts in 1976; the number of nests had
increased 36 percent in 22 years. The ratio of cen-
sused kittiwakes to nests on St. Paul Island was 1.4
(Hickey and Craighead 1977). If this value has been
constant over 22 years, the rate of increase in the
kittiwake population can be estimated at 1.4 percent
a year.
Black-legged Kittiwakes were an important food
item for the Pribilof Aleuts (Preble and McAtee
1923). Since the early 1920's, the Aleut community
has become dependent on a wage economy and ex-
erts much less hunting pressure on local seabird and
marine mammal populations. Black-legged Kitti-
wakes are no longer hunted for food, unlike the Red-
legged Kittiwake, which is still hunted at the Pribi-
lofs and whose numbers have remained constant
(Hunt et al. in preparation). The kittiwake popula-
tion in Europe is also increasing; protective legislation
was passed at the end of the last century which re-
moved man as a predator (Coulson 1974). The
cessation of hunting pressure in the Bering Sea
colonies may be the cause of the increase in Black-
legged Kittiwake populations.
Reproductive biology
Studies of the reproductive biology of Black-
legged Kittiwakes were conducted for several years in
Norton Sound (Ramsdell and Drury 1979) and on the
Pribilof Islands (Hunt et al. in preparation), and for
one or two years at Cape Peirce (Dick and Dick 1971,
Petersen and Sigman 1977), Little Diomede Island
and Fairway Rock (Biderman and Drury 1978), St.
Lawrence Island (Searing 1977), and King Island
(Biderman and Drury 1978). Other long-term studies
are available for neighboring areas: Cape Thompson
in the southern Chukchi Sea (Swartz 1966, Springer
and Roseneau 1978), and Kodiak Island in the Gulf
of Alaska (Nysewander and Barbour 1979, Baird and
Hatch 1979). Studies of kittiwakes in the Atlantic by
Coulson (Coulson 1963, 1966, 1968, 1974; Coulson
and White 1958, 1959, 1960, 1961; Coulson and
Wooler 1976), Cullen (1957), and others provide ex-
cellent data for comparison with Bering Sea kitti-
wakes.
Phenology
In the Bering Sea, Black-legged Kittiwakes re-
occupy their colonies between late April and mid-
May. There appears to be a gradient in the timing of
egg-laying from south to north (Table 39-3). Around
the northern colonies the persistence of pack ice in
spring inhibits feeding and social gathering, while
snow packs block access to the nesting ledges. How-
ever, differences in timing between regions are about
equal in magnitude to local variations in timing
caused by annual changes in weather and food
availability.
,-.
170
165 1^
150
*T
"^7
/
•
• • •
/
•%.
•
▼
%
h ■
BLACK -LEGGED KlTTrWAKE
•
•
•
■■
Colony S>ze
. 1-100 buds
•
• 101 1.000 brfds
^'r
• lOOf- 10.000 b.rds
9 10.001-100.000 birds
^100,001-1.000.000 birds
.:▼
•
▼ Unknown number ol birds
^
Figure 39-8. Black-legged Kittiwake colonies in the Bering
Sea.
658 Marine birds
TABLE 39-3
Initiation of egg-laying in Blaci< -legged Kittiwakes in the Bering Sea
Northern colonies
Initiation of laying
X laying
Little Diomede Island
(Biderman and Drury 1978)
King Island
(Drury and Steele 1977)
Bluff
(Ramsdell and Drury 1979)
St. Lawrence Island
(Searing 1977)
28 June 1977
around 20 June 1976
25 June 1976
22 June 1977
18 June 1978
late June
29 June 1976
12 July 1977
30 June-3 July*
4-7 July 1977*
22-25 June 1978*
Southern Colonies
Cape Peirce
(Dick and Dick 1971,
Petersen and Sigman 1977)
St. Paul Island
(Hunt et al. in preparation)
St. George Island
(Hunt et al. in preparation)
4 June 1970
10 June 1976
15 June 1975
18 June 1976
21 June 1977
18 June 1978
18 June 1976
20 June 1977
15 June 1978
20 June 1976
5 July 1975
29 June 1976
30 June 1977
30 June 1978
1 July 1976
30 June 1977
3 July 1978
*Mean expressed as a range because of observational uncertainty.
Atlantic kittiwakes arrive at tiieir colonies as early
as January in the southern part of their range, and
March in the Arctic (Coulson 1974). Egg-laying be-
gins in late April or mid-May, although it may begin
later in the more northern colonies. A north-south
gradient in phenology similar to that seen in the Be-
ring Sea (Table 39-3) also appears in the Atlantic. In
the southern colonies in England, egg-laying extends
into July, resulting in a longer period of laying, since
laying in the southern colonies begins earlier than in
the northern colonies (Coulson 1974). Atlantic kitti-
wakes appear to exhibit less fluctuation in phenology
from year to year than those in the Bering Sea.
Although Black-legged Kittiwakes in the Bering Sea
begin breeding much later than those in the Atlantic,
the length of the actual nesting period, from egg-
laying through fledging, is very similar. An average
incubation period of 27 days was found in studies of
kittiwakes on the Pribilofs, in Norton Sound, and in
Europe. Similarly, the nestling period at each loca-
tion averaged 42-44 days (Coulson and White 1958,
Hunt et al. in preparation, Ramsdell and Drury
1979).
In the Bering Sea, hatching begins slightly earlier in
the southern than in the northern colonies. Hatching
begins in mid-July and continues into mid-August,
Annual variations in commencement of hatching
from a few days to two weeks have been observed.
Black-legged Kittiwakes lay clutches of one to four
eggs (Belopolskii 1957). Kittiwakes lay smaller
clutches (one, two, or rarely, three eggs) in the
Bering Sea region, and there has been considerable
fluctuation in the frequency of one- and two-egg
clutches (Table 39-4). Two eggs per clutch is the
usual in the Atlantic, although three-egg clutches
are common, with inexperienced breeders generally
producing smaller clutches (Coulson 1974). Clutches
in the Bering Sea colonies are generally smaller than
Breeding dislribution and reproductive biology 659
TABLE 39-4
Variation in clutch size of Black-legged Kittiwakes
Bering Sea
1960
1961
1975
1976
1977
1978
Cape Thompson
(Springer and
Roseneau 1978)
Bluff
(Drury and Steele 1977,
Biderman et al. 1978,
Ramsdeli and Drury 1979)
St. Paul Island
(Hunt et al. in preparation)
St. deorge Island
(Hunt et al. in preparation)
Kulichkof Island
(Hatch etal. 1978)
Sitkalidak Strait
(Hatch etal. 1978)
1.92
1.88
0.29
1.42
1.16
1.20
1.70
1.49
1.52
1.33
1.42
1.46
1.20
1.91
1.72
1.68
1.26
Barents Sea
1937
1938
1939
1940
Kharlov Island
(Belopolskii 1957)
2.33
1.53
1.74
2.03
Atlantic Ocean
Northumberland, England
(Coulson 1966)
1st time breeding
2nd time breeding
3rd time breeding
5th or 6th time breeding
after 6th time breeding
1.78
2.00
2.11
2.15
2.24
those of birds breeding for the first time in North-
umberland.
At some colonies in the Chukchi and Bering seas,
the size of kittiwake clutches may have been larger
in the past. At Cape Thompson in the southern
Chukchi Sea, mean clutch size was 1.92 in 1960 and
1.88 in 1961 (Swartz 1966); in 1977, when Springer
and Roseneau (1978) continued the study, mean
clutch size had dropped to 1.20. Data are insufficient
to determine if these smaller clutch sizes were indica-
tive of a trend or just symptomatic of the yearly fluc-
tuations that characterize many aspects of kittiwake
breeding biology. Kittiwakes at Cape Thompson ex-
perienced reproductive failure in 1977 and the re-
duced clutch size may be a persistent effect of the
environmental factors which led to the previous
year's failure. Clutch size has fluctuated on the Prib-
ilofs. Preble and McAtee (1923) reported that clutch
size was usually two and occasionally three eggs per
nest. When Kenyon and Phillips (1965) visited the
islands in the 1950's, the maximum clutch size for
Black-legged Kittiwake was two eggs. A two-egg
maximum was also found in 1975-79 (Hunt et al. in
preparation).
660 Marine birds
Productivity
The reproductive success of Bering Sea kittiwakes
varies among regions and among years. The Pribilof
Island colonies, near the edge of the continental shelf,
have the most stable productivity. The northern
colonies are typified by year-to-year extremes of suc-
cess and failure. Poor reproductive years are charac-
terized by three conditions: fewer nests receive eggs,
clutch size is smaller, and egg mortality increases.
The reproductive success of Black-legged Kitti-
wakes is sensitive to variations in weather and food
availability. Brood reduction is a mechanism for
maximizing reproductive success (O'Conner 1978)
and appears to occur in Bering Sea kittiwakes. Rams-
dell and Drury (1979) mention that in nests where
chicks hatched within a day of each other, the
chances of both chicks fledging were much greater
than if hatching was asynchronous. Braun (in pre-
paration) hypothesized that siblicide occurs as a
response to lowered food availability, and the occur-
rence of siblicide is mediated by both parental and
chick behaviors. The extent of chick aggression
appears closely linked to the energy balance of the
chicks. Brood reduction has not been reported for
the Atlantic populations of kittiwakes.
Growth rates are a sensitive indicator of food limi-
tation. Table 39-5 shows that even in years of high
reproductive success. Black-legged Kittiwake chicks in
the Bering Sea grow at a slower rate than chicks in
Atlantic colonies nurtured by birds breeding for the
first time. The highest kittiwake growrth rates mea-
sured in the Bering Sea, at Bluff in 1978 and St. Paul
in 1978 and 1979 (Table 39-5), approach those seen
in the Atlantic. The lower growth rates suggest that
in many years food is limiting for Bering Sea kitti-
wakes.
Table 39-6 shows kittiwake productivity in the
Bering Sea. Throughout most of the Bering Sea,
yearly Black-legged Kittiwake reproductive success is
highly variable. In contrast, the reproductive success
of the Atlantic kittiwakes is high and stable (Table
39-7). Bering Sea kittiwakes characteristically have
much lower productivity than Atlantic kittiwakes,
with many years of low productivity and relatively
few years of high productivity.
An interesting question, considering the geographi-
cal variation in reproductive success of kittiwakes, is
whether some colonies frequently fail to produce
enough young for population stability while others
regularly attain this level or even produce enough
young for colony growth or emigration. In order to
maintain the size of their populations, many Bering
Sea colonies may rely on infrequent years of high
productivity or on immigration from more productive
TABLE 39-5
Growth rates of Black-legged Kittiwake chicks (gram/day)
1975
1976
1977
1978
1979
Bering Sea
Bluff
15.6
(Ramsdell and
Drury 1979)
St. Paul Island
14.6
12.8
14.5
15.1
16.6*
(Hunt et al. in prep.)
St. George Island
11.5
13.8
13.0
(Hunt et al. in prep.)
Chukchi Sea
Cape Thompson
14.2
(Springer and
Roseneau 1978)
North Atlantic
Northumberland
(Coulson and
White 1958)
broods of one
1st time
15.81
experienced
15.57
broods of two
1st time
14.75
experienced
16.67
*Growth rate may be high since measurements were taken
over a shorter period.
colonies. The colonies at the Pribilof s show a fairly
stable population with slight growth, and so may
serve as an "export" colony. In the Gulf of Alaska,
we would expect kittiwake populations to be increas-
ing, due to their higher productivity.
Overview
Coulson and others have related the timing of
breeding and clutch size to the age and experience of
breeding Black-legged Kittiwakes, the location of the
nest, and density in the breeding colonies. While
these same influences are probably acting in Bering
Sea kittiwake colonies, it is difficult to believe that
the delayed phenology and smaller clutch sizes ob-
served in the Bering Sea are solely caused by the en-
tire Bering Sea kittiwake population's consisting of
young and inexperienced birds. On the Pribilofs,we
banded a few breeding adults five years ago, and
while they appear to have higher productivity than
the average, they are still well below the level of re-
productive success and clutch size achieved by first-
time breeders in the Atlantic. Although age-related
differences in productivity found by Coulson and
Breeding distribution and rcpruductiue biology 661
TABLE 39-6
Estimates of reproductive success of Biaci<-legged Kittiwakes
in the Pacific (chicks fledged per nest)
1960 1961 1976
Chukchi Sea
Cape Thompson
(Springer and
Roseneau 1978)
(chicks fledged/
egg laid)
0.65
0.41
failure
1977
0.64
1975 1976 1977
1978
Northern Bering Sea
Norton Sound, Bluff
Southern Bering Sea
St. Paul Island,
Pribilof Islands
(Hunt et al. in prep.)
St. George Island,
Pribilof Islands
(Hunt et al. in prep.)
Cape Peirce
(Petersen and Sigman 1977
Gulf of Alaska
Kulichkof Island
(Nysewander and
Barbour 1979)
Sitkalidak Strait
(Baird and Hatch 1979)
0.48
0.51
0.04 0.11 0.82
0.61 0.59 0.38
0.66 0.48 0.29
0.25 failure
1.23 0.77
0.74 0.17
White (1958, 1960) in the Atlantic also affect the
Bering Sea population, the differences between
the Pacific and Atlantic kittiwake populations in
phenology, clutch size, and productivity probably
are also related to the availability of food.
The availability of food can be affected by several
factors: variations in the size of populations of prey
species, changes in the temporal or spatial distribu-
tion of prey species, intraspecific or interspecific
TABLE 39-7
Reproductive success in Black-legged Kittiwakes as a
function of breeding experience,
Northumberland, England
Chicks fledged/nest (Coulson and White 1958)
1st time breeding
2nd time breeding
3rd time breeding
0.66
1.21
1.63
competition, and the frequency of storms which may
interrupt foraging. Different factors appear to be in
effect in different regions in the Bering Sea.
On the basis of oceanographic and fisheries data,
there is no evidence that food for seabirds is limiting
in the Bering Sea as a whole. The Bering is a very
rich ocean, with high values of primary productivity
and large fish populations. However, the distribution
of fish and invertebrate prey species is not uniform.
The southeastern Bering Sea has much larger fish pop-
ulations than the northeastern regions and is an im-
portant nursery area for many species, including wall-
eye pollock (Theragra chalcogramma), salmon (Onco-
rhynchus), and capelin (Mallotus villosus). Corre-
spondingly, kittiwake numbers in this region are ten
times greater than in the northern Bering Sea (Sowls
etal. 1978).
Food availability may be limited on a local basis.
While the southeastern kittiwake colonies aire prob-
ably not limited by the size of prey species popula-
tions, the availability of food may be affected by
inter- and intraspecific interference competition by
foraging birds. Furthermore, the consistently poor
weather in this region is a complicating factor, af-
fecting the reproductive and foraging success of the
seabirds and the reproduction of their prey species.
For instance, the success of walleye pollock breeding
depends on a few storm-free days in April, just after
the fish hatch out (Cooney et al. 1978). Storms
during this period reduce the numbers of first-year
pollock, a major food source for the kittiwakes (Hunt
et al.. Chapter 38, this volume).
In Norton Sound and the Chukchi Sea, changes in
the temporal or spatial distribution of prey species
appear to have a major impact on the reproductive
success of the kittiwakes. Weather is generally less
severe in this region, although occasional severe
storms do affect survival of young, lengthen foraging
time, or interrupt foraging (Ramsdell and Drury
1979). The increased exposure or break in the food
supply to the young due to storms can have disas-
trous effects.
Kittiwakes breeding in different regions of the Be-
ring Sea rely on different prey species (summarized in
Hunt et al., Chapter 38, this volume). How stable
productivity is in these colonies depends upon the de-
gree to which food resources are accessible and de-
pendably available. For instance, on the Pribilofs,
near the rich marine community at the shelf edge.
Black-legged Kittiwakes use a diverse food supply
without total dependence on any single species. The
Pribilof colonies are unique in the Bering Sea for their
stable but moderate productivity. Most nests pro-
duce a single chick and even in exceptional years only
662 Marine birds
a few nests fledge two young. In contrast, the north-
em colonies, dependent on migrations of sand lance
(Ammodytes hexapterus), are typified by "boom and
bust" years (Ramsdell and Drury 1979). In years
when the sand lance come within the feeding range
of the breeding kittiwakes, many nests fledge two
young, while in other years, entire colonies may fail.
For example, 16 percent of the kittiwake nests at
Bluff colony fledged two young in 1978, with an av-
erage success of 0.82 chicks fledged per nest built,
whereas in 1976, only 5 chicks fledged from the 47
nests receiving eggs and average productivity was
0.04 chicks fledged per nest (Drury and Steele 1977,
Ramsdell and Drury 1979).
While the availability of food is an important de-
terminant of the levels of success, it is not the sole
determinant. Weather, competition, and how long
ice persists around the colony all affect productivity.
165 170 175 IH. . 175
170
I6S 160 156
150
r^-^^rrT^--^^^^^^m-mmM^gM^
"■■■5-S':'Sx>::S^;S>::v:v-K^
^^^i^
II s iiiii
RED-LEGGED KITTIWAKE
■"'■ S>:-:-:-x^S:5iS>
>-||||i|" _;
Colony SiiO
wy M
• 10 00 1-100,000 birds
T unknown number ol b.rdn
•
•
•
Figure 39-9. Red-legged Kittiwake colonies in the Bering
Sea.
Red-legged Kittiwake (Rissa brevirostris)
Distribution
Red-legged Kittiwakes are endemic to the Bering
Sea but are rare outside their breeding range (Kessel
and Gibson 1978). This species breeds only on the
Pribilof Islands, on Buldir and Bogoslof Islands in the
Aleutian Chain, and on the Komandorsky Islands
(Sowlsetal. 1978).
Habitat
On St. George Island in the Pribilofs, Red-legged
Kittiwakes nest in large single-species aggregations on
the highest cliffs; on lower cliffs, such as on St. Paul
or Buldir islands (Byrd 1978), they nest singly or in
small clusters among Black-legged Kittiwakes. On the
Pribilof Islands, Red-legged Kittiwakes prefer to nest
on ledges which are sheltered by an overhang and on
ledges smaller than those preferred by Black-legged
Kittiwakes (Hunt et al. in preparation).
Colonies
This species is knovm to breed in only four areas,
nesting in both large and small colonies (Fig. 39-9).
Of the estimated world population of Red-legged
Kittiwakes, 88 percent, amounting to 220,000 birds,
nest on St. George Island (Hickey and Craighead
1977, Hunt et al. in preparation). Buldir Island has
an estimated 2,000 breeding pairs (Byrd 1978), while
Bogoslof Island has only 200 (Kessel and Gibson
1978). The status of the Red-legged Kittiwake on the
Komandorsky Islands is uncertain.
The Red-legged Kittiwake is a surface-feeding sea-
bird that specializes on deep-water fish, myctophids.
The shelf break, between the 200-m and 2,000-m iso-
baths (Fig. 39-9), is an area of steep gradient where
deep-water fish may be found. Red-legged Kittiwakes
nest only on islands that are close to the shelf break
and that provide cliff habitat for nesting. St. Mat-
thew Island has the required high cliffs, but it is 230
km from the shelf break— apparently greater than the
foraging range of Red-legged Kittiwakes, since this is-
land is not used for nesting (Sowls et al. 1978). Why
more islands in the Aleutian chain are not breeding
sites for Red-legged Kittiwakes is not known.
Status of the Bering Sea population
The population of Red-legged Kittiwakes in the
eastern Bering Sea is estimated at 250,000 (Sowls et
al. 1978). The status of this population is unknown.
Some reports from the late 1800's indicated that
Red-legged Kittiwakes nested on many of the Aleu-
tian Islands. Gabrielson and Lincoln (1959) dis-
counted these reports when other investigators failed
to confirm them. On St. Paul Island in the Pribilofs,
the Red-legged Kittiwake population appears to be
stable. Counts of nests made at specific locations
around the island in 1954 (Kenyon and Phillips
1965) were repeated in 1976 with identical results
(Hunt 1977).
Reproductive biology
Red-legged Kittiwakes have been studied exten-
sively on the Pribilof Islands by Hunt (1976, 1977)
and Hunt et al. (1978, in preparation).
Breeding dislrihution and reproductive biology 663
I
Phenology
On the Pribilof Islands, Red-legged Kittiwakes lay a
single egg in the second half of June. In the past,
Red-legged Kittiwakes occasionally laid two eggs
(Kenyon and Phillips 1965); at least since 1975, the
maximum clutch size has been one (Hunt et al., in
preparation). Incubation averages 29 days; most
chicks hatch by eairly August. Chicks spend about
37 days in the nest; flying young continue to be fed
by the parents for at least a week more.
The events of the breeding cycle in the Red-legged
Kittiwake population occurred about a week later
than those of the Black-legged Kittiwakes on the Prib-
ilofs between 1975 and 1978 (Hunt et al. in prepara-
tion). Kenyon and Phillips (1965) also found Black-
legged Kittiwakes breeding about a week earlier than
Red-legged Kittiwakes in 1954.
Productivity
Although on the Pribilof Islands Red-legged Kitti-
wakes lay only a single egg, generally they are as pro-
ductive as Black-legged Kittiwakes that lay an average
of 1.5 eggs per clutch. Over a four-year period, Red-
legged Kittiwakes fledged an average of 0.38 young
per nest attempt while the Black-legged Kittiwakes
fledged an average of 0.43 young per nest attempt
(Hunt et al. in preparation).
Arctic Tern (Sterna paradisaea)
Distribution
Arctic Terns breed in the northern hemisphere and
winter in the oceans of the southern hemisphere
(Godfrey 1966). In their breeding range they are cir-
cumpolar, using the arctic and subarctic regions of
both the old and new worlds. In the Bering Sea they
are congregated in Norton Sound at Safety Lagoon as
well as being scattered in single pairs or small groups
along the shore of the Seward Peninsula and the west-
em Aleutian Islands and around Nunivak Island.
Their colonies are found in much greater numbers on
the Kodiak Archipelago in the Gulf of Alaska.
Habitat
Arctic Terns nest in both coastal and interior re-
gions near both fresh and salt water. They nest on
sandpits, sand or gravel beaches, tundra, river deltas,
rocky shores, or islands (Godfrey 1966). Arctic
Terns avoid nesting in tall vegetation, preferring open
areas with low vegetation (Hawksley 1957, Baird in
preparation). Baird and Moe (1978) found that Arc-
tic Terns were much more likely than Aleutian Terns
to nest on slopes.
Colonies
Arctic Tern colonies are known to shift location in
response to such alterations in the environment as
changes in vegetation or the introduction of gulls or
other predators (Hawksley 1957). Their colonies
tend to be small; most of the Bering Sea colonies
harbor fewer than 50 pairs (Fig. 39-10). In about
18 percent of Alaskan Arctic Tern colonies the num-
ber of inhabitants is unknown.
Status of the Bering Sea population
The eastern Bering Sea population of Arctic Terns
is estimated to be just under 2,000 (Sowls et al.
1978). Their status is unknown.
Reproductive biology
The reproductive biology of Arctic Terns has not
been studied in the Bering Sea. The information re-
ported here is the result of several extensive studies of
terns by U.S. Fish and Wildlife Service teams working
in the Gulf of Alaska. These studies (Baird and Moe
1978, Baird et al. 1979, Nysewander and Barbour
1979) are summarized in Baird (in preparation).
Phenology
Arctic Terns arrive at the Kodiak Island colonies
between the first and second weeks in May (Baird in
preparation). In the southeastern Gulf of Alaska,
they arrive on the colonies, Hinchinbrook and Naked
islands, about a week earlier (Baird in preparation).
Although terns airrive later than other seabirds nesting
170" 175 180
175
170
165
i6(r
155*
150'
i
::i/li..
:■:■:■--:■:■:
T
:.,;v.:.:™„.::0b5s .HSBI
%*
W^^ '^' '
^tt
>
•SS^
't
,;
^i
ARCTIC TERN
Colony Sue
. 1-100 birds
• 101- 1,000 birds
• 1001-10.000 birds
W 10,001-100.000 birds
^ 100.00 1 - 1.000.000 birds
▼ Unknown number of birds
Figure 39-10. Arctic Tern colonies in the Bering Sea.
664 Marine birds
in the same area, they are the first to lay eggs. At the
Kodiak Island colonies, terns began laying between
22 and 31 May in 1977 and 1978. Eggs are laid over
a prolonged period, as much as a month and a half,
which often overlaps hatching in the same colony.
The incubation period averages 21 days (Baird in pre-
paration). Hatching begins in mid-June with most
chicks hatching during July (Baird in preparation).
The nestling period lasts about 28 days; fledging be-
gins in mid-July (Baird in preparation). By mid-
August, most terns have left their colonies.
Productivity
Mean clutch size varied between colonies and
between years, ranging from 1.79 eggs per nest to
2.31 eggs per nest (Baird in preparation). Tern pro-
ductivity may fluctuate greatly from one year to the
next (Baird in preparation). On Kodiak Island, Arctic
Terns produced between 0.28 and 1.06 chicks per
nest in 1977. In 1978, productivity dropped in re-
sponse to increased avian predation of eggs and
chicks, a result of adults spending less time on their
nests. Lowered nest attentiveness was thought to re-
flect a reduced food supply in 1978, forcing adults to
spend more time foraging (Baird in preparation). Pro-
ductivity can be severely reduced by storms during
the hatching period, as at Chiniak Bay in 1977 and at
Sitkalidak Strait in 1977 and 1978. Disturbance of
the colonies by mammalian predators or human
activities may also seriously affect local productivity,
as at Amee and Sheep islands and on mainland
Kodiak in 1978, and at Sitkalidak Strait in 1977 and
1978 (Baird in preparation). Terns may recover their
losses by the production of a second clutch.
Aleutian Tern (Sterna aleutica)
Distribution
Aleutian Terns have a more limited breeding range
than Arctic Terns. Aleutian Terns breed from the
southern Chukchi Sea, south along both coasts of the
Bering Sea, along the Aleutian Chain, and through the
Gulf of Alaska (Kessel and Gibson 1978). They re-
main in the northern oceans in winter (Austin and
Kuroda 1953), but leave their breeding areas and con-
centrate around Japan (Baird in preparation).
Habitat
These birds are ground-nesters, preferring to place
their colonies near lagoons, river mouths, on sandbar
islands, or on the flat tops of coastal islands (Gabriel-
son and Lincoln 1959). On Kodiak Island, Aleutian
Terns nested in the same type of vegetation as Arctic
Terns; the main difference in nesting habitat was that
Aleutian Terns preferred lower elevations and flatter
terrain (Baird in preparation).
Colonies
Aleutian Terns are known to shift the location of
their colonies from year to year; only the largest
colonies are stable. Nysewander and Barbour (1979)
found that the colonies most likely to vary either in
number of birds nesting or in density were either
small colonies or those that had been subjected
to mammalian predation the preceding yeair. The two
largest colonies are at Port Moller with 1,000 birds
and at Goodnews Bay with 600 birds (So wis et al.
1978) (Fig. 39-11). Aleutian Terns frequently nest in
mixed colonies with Arctic Terns.
Status of the Bering Sea population
The eastern Bering Sea population of Aleutian
Terns is estimated at 5,000 birds (Sowls et al. 1978).
The status of this population is unknoMm.
Reproductive biology
This species is the least studied of the North Amer-
ican terns (Gill and Dick 1977). The bulk of informa-
tion has been gathered by U.S. Fish and Wildlife Ser-
vice teams between 1975 and 1978 working in the
vicinity of Kodiak Island in the Gulf of Alaska (Baird
and Moe 1978, Baird et al. 1979, Nysewander and
Barbour 1979, Baird in preparation).
Phenology
Kessel and Gibson (1978) report that Aleutian
Terns arrive earliest at their eastern colonies, in late
1
■;;:i:;|:;i.. *
imrnmrnMsM
1
■^K'i ^-
f-x^-^-^
•
ALEUTIAN TERN
-w*
Colony Sue
. 1-100 birds
• 10 1- 1.000 birds
• 1001 10,000 bKds
W 10,001 100.000 birds
^100 cot 1.000.000 birds
▼ Unknown number ol birds
"*■*!
^^"^^^
:-,^T'
/
Figure 39-11. Aleutian Tern colonies in the Bering Sea.
Breeding dislrihuliun and rcpruductiuc biology 665
April or early May, and a few weeks later at the
northern and western colonies. Where Arctic and
Aleutian Terns nest together, the Aleutian Terns
show slightly delayed phenology relative to Arctic
Terns: they arrive a few days later and their nesting
chronology is about a week behind (Baird in prepara-
tion). Aleutian Terns start laying within two weeks
of their arrival. As in Arctic Terns, egg-laying is very
prolonged. The incubation period averages 22 days
(Baird in preparation); the nestling period is similar to
that of Arctic Terns. Aleutian Tern chicks continue
to be fed by the parents for one to two weeks after
they are able to fly (Baird in preparation). Adults
and chicks leave the colonies by mid-August.
Productivity
Reproductive biology of Aleutian Terns was studied
at Chiniak Bay and Sitkalidak Strait on Kodiak Island
in 1977 and 1978. Mean clutch size varied between
the colonies and between years, ranging from 1.5 to
2.0 eggs per nest. Many Aleutian Tern colonies near
Chiniak Bay failed (Nysewander and Barbour 1979).
In 1977, mortality occurred primarily during the
chick stage, and the major causes were predation by
river otters and exposure or starvation caused by
storms. In 1978, mortality occurred primarily in the
egg stage and was caused by weasel predation. In
1977, Aleutian Terns at Sitkalidak Strait fledged be-
tween 0.21 and 0.83 chicks per nest-with-eggs (Baird
in preparation). In 1978 productivity decreased, pos-
sibly in response to lowered food availability (Baird
in preparation).
ALCIDAE
The Northern Hemisphere is the center of adaptive
radiation for this family of diving seabirds (Bedard
1969a) that occupies the ecological foraging zone of
the subsurface waters. The range of sizes and the va-
riety of life history strategies among the species make
this family of seabirds one of the most interesting.
There is differentiation between species in the selec-
tion of foraging areas; moreover, the distribution of
alcid nesting colonies may reflect the availability of
preferred foods, which in turn are restricted to partic-
ular water masses or ocean environments.
Common Murre (Uria aalge)
Distribution
Common Murres breed in the North Pacific along
coasts and on islands from the Bering Strait south to
California and west to Japan (Tuck 1960, Godfrey
1966). In the North Atlantic Ocean, they breed from
the arctic regions south to northern France and west
to Nova Scotia. In addition to some movement
southward, Common Murres are thought to winter in
the ice-free portions of their breeding range
(Gabrielson and Lincoln 1959).
Habitat
Common Murres nest on the tops of flat, rocky,
predator-free islands and on broad cliff ledges
(Gabrielson and Lincoln 1959). Some Common
Murres nest on narrow ledges with Thick-billed
Murres (Hunt et al. in preparation).
Colonies
Common Murres occur in mixed colonies with
Thick-billed Murres throughout much of their range
in the Bering Sea (Figs. 39-12, 39-13). In many places
where these two species occur together, one or the
other usually makes up the vast majority, but in the
northern Bering Sea the two may be present in almost
equal numbers. Nearly pure Common Murre colonies
occur in coastal waters, such as the Cape Peirce
(Petersen and Sigman 1977) and Norton Sound
colonies (Biderman et al. 1978), in which 99 per-
cent of the murre populations are Common Murres.
On the Pribilof Islands a small percentage of Common
Murres nest among the more numerous Thick-billed
Murres (Hickey and Craighead 1977). Colonies of
Common Murres range in size from fewer than 100
birds to more than 500,000 (Fig. 39-13), but most
are between 10,000 and 100,000 birds.
Status of the Bering Sea population
There are an estimated 4.9 million Common
Murres in the eastern Bering Sea. The status of this
^^0^ IT'. 17
!70 165
150
^^M...:.:.
%
,,.
• _ _
• • •
/
4%v
" •&.■!.••
ALL MURRES
Colony Size
•g
. 1-100 birds
• 10 1-1,000 birds
• 100 1 10,000 birds
W 10,001 100,000 birds
^100,00 1 t 000,000 birds
Q over I 000 000 birds
W Unknown number ol birds
•
Figure 39-12. Ahirre colonies in the Bering Sea.
666 Marine birds
170 175- 180'
:75''
170° 165'
160-
155" 150
ijS:: ^ ^ r^n..^ ^
111
'^
t-f
iiiiiiil/Ji.:
siiiisP*™ ■■■■■■«"'
T /
J
ft--- i"-
t
\
-_- ■%
I
x
■&
¥
r
A
• >
;V
L„,.,,y '
^
^V
«» ^
COMMON MURRE
Colony Size
.^ :-:■:-
. 1-100 birds
^
▼
" 101-1,000 birds
• 1001-10,000 buds
^10,001-100,000 b.rds
/^ c
1
-^;f r ■
'
^100,001-1.000,000 birds
(
▼ Unknown number ol birds
/,.r-
Figure 39-13. Common Murre colonies in the Bering Sea.
population is unknown. However, the Common
Murre colony on Walrus Island in the Pribilofs has dis-
appeared during this century. In the early 1900's,
this island supported one of the largest murre colo-
nies in the world (Preble and McAtee 1923). The
murres have gradually been displaced by a growing
colony of Steller sea lions (Kenyon and Phillips 1965,
Huntetal. 1978).
Reproductive biology
In the Bering Sea, Common Murres have been
studied at Cape Peirce (Petersen and Sigman 1977,
Dick and Dick 1971), on the Pribilof Islands (Hunt et
al. in preparation), St. Lav^nrence Island (Searing
1977), Little Diomede Island (Biderman and Drury
1978), and in Norton Sound (Drury and Steele 1977,
Biderman et al. 1978, Ramsdell and Drury 1979).
Comparative data for this species exist from studies
conducted in the Atlantic (Birkhead 1977a, b; Birk-
head and Hudson 1977; Tuck 1960). Birkhead
(1977b) found that the breeding success of Common
Murres undisturbed by investigators was highest on
ledges with high densities of birds and lowest where
birds were sparse. The difference in reproductive
success resulted from the better ability of murres at
higher densities to drive off gulls attempting to steal
eggs or chicks.
Phenology
Common Murres arrive at their colonies in April.
They start laying in eairly June at Cape Peirce (Peter-
sen and Sigman 1977); in the other Bering Sea colo-
nies, laying begins in late June. Peak laying appears
to be earliest at Cape Peirce (in mid-June: Petersen
and Sigman 1977), later on the Pribilofs (in the first
week of July: Hunt et al. in preparation), and latest
in Norton Sound (mid-July: Drury and Steele 1977,
Biderman et al. 1978). Phenology is difficult to es-
tablish with certainty since it is sensitive to disturb-
ance. Disturbance causes the laying and hatching
periods to be extended and delays their peaks, since
eggs are lost and must be relaid. Of the two species
of murres, Common Murres are probably more sensi-
tive to disturbance because of crowding on the nest-
ing ledges. Eggs are lost both when birds are scared
off their ledges and also during the jostling that oc-
curs when birds return (G. Hunt, personal observa-
tion).
The average length of incubation on the Pribilof Is-
lands was 31 days (Hunt et al. 1978). Peak hatching
occurred between the last week in July and the third
week in August. As in other species, hatching appears
to occur earlier in southern than in northern colonies.
Chicks remained on the ledges approximately 21 days
before going to sea (Hunt et al. in preparation).
Productivity
Even the most cautious observer is bound to inter-
fere with the potential reproductive success of murres
by scaring adults off eggs and chicks. Moreover, the
crowded conditions on the ledges make it difficult to
tell whether an adult is nesting or is a loiterer. Hence,
even though Common Murres occur in many study
areas throughout the Bering Sea, little unequivocal in-
formation about their breeding biology has been
gathered.
Reproductive success has varied widely from site to
site within a colony, depending on the structure of
the nesting ledge, the number of birds on the ledge,
and the amount of observer-caused disturbance.
Table 39-8 shows estimates of productivity for colo-
nies of Common Murres in the Bering Sea. On the
Pribilof Islands, productivity of sites studied with a
minimal amount of observer-initiated disturbance av-
eraged 0.62 chicks fledged per egg laid. Bluff colony
in Norton Sound had similar productivity. On St.
Lawrence Island productivity values are available only
for Uria species.
Birkhead and Hudson (1977), working in Wales,
estimated an average life expectancy for adult Com-
mon Murres of 11 years, requiring that 17 chicks per
hundred adult pairs survive to enter the breeding pop-
ulation if a stable population was to be maintained.
Production of 70 chicks per 100 pairs was required if
17 chicks were to survive to breeding age.
Brecdinfi dislribuliun and reproductive biology 667
TABLE 39-8
Estimates of reproductive success of Common Murres
in the Bering Sea
(chicks fledged per egg laid)
17b 170' 165
1976
1977 1978
Norton Sound, Bluff
(Drury and Steele 1977,
Bidermanetal. 1978,
Ramsdell and Drury 1979)
St. Lawrence Island
(Searing 1977)
St. Paul, Pribilof Islands
(Hunt et al. in preparation)
St. George, Pribilof Islands
(Hunt et al. in preparation)
0.29-0.40 0.74 0.73
0.61 (Uria species)
0.56 0.61
0.70
Thick-billed Murre (Uria lomuia)
Distribution
Thick-billed Murres breed along the coasts and on
islands throughout the arctic and subarctic regions of
the Northern Hemisphere (Tuck 1960, Godfrey
1966). In the Pacific, the southern boundary of their
breeding range is Middleton Island in the Gulf of
Alaska (Sowls et al. 1978). They are thought to win-
ter in the ice-free regions of the southern part of their
breeding range. Tuck (1960) reports that they also
range south to the 5 C ocean isotherm, from northern
British Columbia to Japan.
Habitat
Thick-billed Murres nest on narrow ledges on the
faces of sea cliffs. In the absence of predators, they
also nest on low, rocky islands (Gabrielson and
Lincoln 1959).
Colonies
Thick-billed Murres are probably the most numer-
ous seabird breeding in the Bering Sea (Sowls et al.
1978). The largest murre colony in the Bering Sea
is located on St. George Island: this island alone sup-
ports an estimated 1.5 million Thick-billed Murres
(Hickey and Craighead 1977). Thick-billed Murres
usually nest in large colonies; most of the Bering Sea
colonies contain over 10,000 birds (Fig. 39-14).
According to Sowls et al. (1978), probably no major
murre colonies remain to be discovered. However, in
many colonies there is a need to determine the rela-
tive abundance of the two murre species, since many
current estimates have combined counts (Fig. 39-12).
M
a.
-i"^
THICK-BILLED MURRE
Colony Size
. 1-100 birds
• 101-1.000 birds
• 1001 -10.000 birds
W 10,001 100,000 birds
^100.001-1,000,000 birds
O
o°
.^Ji>-
1 000.000 birds
Figure 39-14. Thick-billed Murre colonies in the Bering
Sea.
Status of the Bering Sea population
The population of Thick-billed Murres in the east-
em Bering Sea is estimated at 4,900,000. However,
this figure will need to be changed as counts are re-
fined (Sowls et al. 1978). The status of this popula-
tion is unknown.
Reproductive biology
Thick-billed Murres have been studied in the Bering
Sea on the Pribilof Islands (Hunt et al. in prepara-
tion), in Norton Sound and the Bering Strait (Drury
and Steele 1977, Biderman et al. 1978, Biderman and
Drury 1978, Ramsdell and Drury 1979), and on St.
Lawrence Island (Searing 1977). Searing did not
separate the two murre species in his investigations.
Thick-billed Murres have also been studied extensive-
ly in the Atlantic (Tuck 1960).
Phenology
Thick-billed Murres usually arrive in the vicinity of
their breeding colonies in April. There may be a few
weeks between arrival and occupation of the ledges.
The persistence of snow on the nesting ledges deter-
mines when the murres start breeding (Searing 1977).
Usually eggs are laid between the end of June and the
end of July. The peak of laying is considerably ear-
lier in the southern colonies than in the north (Table
39-9).
Incubation on the Pribilofs lasted 34 days (Hunt et
al. in preparation); Tuck (1960) records similar pe-
riods in the North Atlantic. Chicks hatch throughout
668 Marine birds
TABLE 39-9
Reproductive biology of Thicl<-billed Murres
in tiie Bering Sea
Peak Chicks fledged/
of laying eggs laid Year
Norton Sound,
Bluff
(Biderman and
Drury 1978)
St. Lawrence
Island
(Searing 1977)
St. Paul,
Pribilofs
(Hunt et al.
in preparation)
St. George,
Pribilofs
(Hunt et al.
in preparation)
15-18 July 1977 0.29-0.40 1976
0.69 1977
1st week July 0.60 1976
30 June 1976
24 June 1977
25 June 1978
2 July 1976
29 June 1977
23 June 1978
0.72 1976
0.35-0.62 1977
0.61-0.68 1978
0.52 1976
0.29-0.57 1977
0.49-0.52 1978
August and remain on the cliffs for about 21 days
(Hunt et aL in preparation) before going to sea with
their parents. The peak of hatching occurs in the
last week of July and the first week in August.
Productivity
Table 39-9 lists productivity of Thick-billed Murres
in different colonies in the Bering Sea. The ranges in
this table represent estimates of maximum and mini-
mum values. Murre chicks are on the nesting ledges
for only two to three weeks and since nonbreeding
birds may maintain an incubating or brooding posture
for weeks, it is difficult to estimate reproductive
success accurately. Patterns of geographical or annual
variation in productivity are obscured by the uncer-
tainty in the productivity data available. Despite
these difficulties, it appears that reproductive success
is fairly consistent for sites studied with a minimal
amount of observer-initiated disturbance (Table
39-9), ranging between 0.5 and 0.7 chicks fledged per
egg laid.
While productivity values appear to be fairly con-
sistent from one colony to another, variation in
growth rates and fledging weights between colonies
may indicate differences in competition or the availa-
bility of food. At the Pribilofs, the Thick-billed
Murre colony on St. George Island is ten times
larger than the one on St. Paul Island, reflecting the
greater abundance of nesting habitat. Murre chicks
on the smaller St. Paul colony consistently grow fast-
er and weigh more at fledging than murre chicks on
St. George Island (Hunt et al. in preparation). These
slight but consistent differences may reflect the im-
portance of intraspecific competition at the larger
colony.
Pigeon Guillemot (Cepphus columba)
Distribution
Pigeon Guillemots breed from the Channel Islands
in California north to Cape Lisburne in the Chukchi
Sea (Sowls et al. 1978, Hunt et al. in press) and west
to the Kurile Islands (Godfrey 1966). They breed
on most of the islands in the Bering Sea except the
PribUofs. Their range overlaps with the Black Guille-
mot (Cepphus grylle) in the northern Bering and
southern Chukchi Seas (Sowls et al. 1978).
Habitat
Pigeon Guillemots nest in crevices at the bases of
rocky coastal cliffs and in talus slopes. They some-
times excavate their own burrows in coastal bluffs
(Godfrey 1966). They are restricted to low eleva-
tions for their nest sites (Sowls et al. 1978).
Colonies
Pigeon Guillemots nest in low densities throughout
the Bering Sea. Most counts of nesting sites show
fewer than 100 birds; these groups are spread along
the coasts and are not in coherent colonies (Fig. 39-
15). Where large numbers of guillemots occur, they
usually form distinct colonies (Sowls et al. 1978).
The largest of these consists of 1,200 birds on Hall
Island (Sowls et al. 1978). St. Matthew and St. Law-
rence islands also have colonies. It is interesting to
note that Pigeon Guillemots are absent from the Prib-
ilof Islands since they occur in fair numbers in sur-
rounding areas and have been recorded on the Prib-
ilofs in winter.
Status of the Bering Sea population
The Bering Sea population is estimated at 30,000
(Sowls et al. 1978). The current status of the popula-
tion is unknovm.
Reproductive biology
The breeding biology of Pigeon Guillemots has not
been studied in the Bering Sea, although the species
occurs in small numbers throughout the region. Sear-
ing (1977) studied the activity cycles of Pigeon
Guillemots on St. Lawrence Island. Biderman et al.
(1978) gives a first-breeding record for this species in
Norton Sound. The breeding biology of Pigeon
Breeding; dislribution and reproductive biology 669
,
)
'
- ■ ■ ' ■ssiiisss
/
'$^
%v ft
^;j.»:::;:::V.'
•?
^ jl
PIGEON GUILLEMOT
,!SiP* '
Colony Sue
. 1-100 birds
• 101-1,000 birds
• 1001-10,000 birds
W 10.001-100,000 birds
^100,001-1,000,000 birds
▼
▼ Unknown number ol birds
▼
Figure 39-15. Pigeon Guillemot colonies in the Bering Sea.
Guillemots in the Pacific has been studied extensively
by Drent (1965) and Thoresen and Booth (1958).
Pigeon Guillemots normally lay two eggs about 3
days apart, and incubate them for around 30 days
(Drent 1965). Chicks spend an average of 35 days in
the nest. After leaving the nest, fledghngs seem to
live an independent existence while the parents con-
tinue to frequent the colony.
Parakeet Auklet (Cyclorrhynchus psittacula)
Distribution
The Parakeet Auklet is endemic to the Bering Sea
and the Northern Gulf of Alaska. Its range includes
the Aleutian Islands, Bristol Bay, the Bering Sea is-
lands, Bering Strait, and Norton Sound (Sowls et al.
1978). It is believed that Parakeet Auklets spend the
winter in the ice-free regions of their breeding range;
however, they have been found as far west as Japan
and as far south as Cahfornia (Sealy 1968, Sowls et
al. 1978).
Habitat
Pairakeet Auklets nest primarily in small caves or
crevices in coastal cliffs; they also nest in talus slopes
or in boulder beaches (Gabrielson and Lincoln 1959,
Sealy and Bedard 1973).
Colonies
Parakeet Auklets are found in the smallest nesting
groups of the Bering Sea auklets. Generally, they
nest in scattered pairs or small groups (Sowls et al.
1978). Large numbers nest on the Pribilof Islands,
St. Lawrence Island, King Island, and Little Diomede
Island (Fig. 39-16).
Status of the Bering Sea population
The population of Parakeet Auklets in the Bering
Sea is estimated to be 530,000 (Sowls et al. 1978).
Estimates for most colonies are poor, and this num-
ber should be used with caution. The status of this
population is unknown.
Reproductive biology
This species has been studied by Bedard (1967,
1969b), Sealy (1968, 1973, 1975), and Sealy and
Bedard (1973) on St. Lawrence Island. These studies
were continued in 1976 by Searing (1977).
Phenology
Parakeet Auklets arrive near their colonies on St.
Lawrence Island between 15 and 20 May. They be-
gin occupying the cliffs about a week after their ar-
rival (Searing 1977). The timing of the events of the
breeding cycle depends upon when the nesting areas
become snow-free (Sealy 1975). The birds lay a
single egg in late June or early July and incubate it
for an average period of 35 days (Sealy 1968). Para-
keet Auklets occasionally relay when their eggs have
been lost (Sealy 1968). Hatching begins at the end of
July; chicks begin to fledge in late August after about
35 days in the nest (Sealy 1968).
PARAKEET AUKLET
■ 101-1,000 buds
^ 1001-10,000 birds
W 10,001-100,000 birds
^^100,001-1,000,000 bird
Figure 39-16. Parakeet Auklet colonies in the Bering Sea.
670 Marine birds
Productivity
On St. Lawrence Island in 1967, reproductive suc-
cess was estimated at 0.52 chicks fledged per nest-
with-eggs (Sealy and Bedard 1973).
Crested Auklet (Aethia cristatella)
Distribution
Crested Auklets are largely endemic to the Bering
Sea, although some colonies are known south of the
Aleutian Islands. Individuals are seen in the Chukchi
Sea although they do not breed there. Crested Auk-
lets breed on most of the Bering Sea islands (Fig. 39-
17) and in the western Aleutian Islands. They winter
in the ice-free regions of their breeding range, al-
though they may be found in winter as far south and
west as Japan (Gabrielson and Lincoln 1959).
Habitat
Crested Auklets nest in tunnels and crevices in
coastal and inland talus and boulder beaches (Bedard
1969b, Sowlsetal. 1978).
Colonies
Crested Auklets occur in large colonies, where they
coexist with larger numbers of Least Auklets and
smaller numbers of Parakeet Auklets. Colonies of
over 20,000 Crested Auklets are found on St. George,
Hall, St. Lawrence, and Little Diomede islands. The
Crested Auklet colonies on St. Lawrence Island alone
total over 400,000 birds (Sowls et al. 1978) (Fig. 39-
17).
170' 165'
^^J^'^;;$
CRESTED AUKLET
-^nW^T^^
Colony Size
. 1-100 birds
• 101-1,000 birds
• 1001- 10,000 birds
%
% 10.001-100,000 bir
ds
* ■
^100,001- 1,000,000
birds
▼ Unknown number o
birds
Figure 39-17. Crested Auklet colonies in the Bering Sea.
Status of the Bering Sea population
The population of crested Auklets in the eastern
Bering Sea is estimated to be 1.2 milhon (Sowls et al.
1978). The status of the population is unknovm, but
numbers may have declined in parts of the Gulf of
Alaska (Sowl 1979). On Diomede and St. Lawrence
islands, it is likely that this species with its specialized
requirements for zooplankton of oceanic origin (Be-
dard 1969c; Cooney 1979; Hunt et al.. Chapter 39,
this volume) may have considerable population fluc-
tuations.
Reproductive biology
The breeding biology of Crested Auklets has been
studied on St. Lawrence Island (Bedard 1967, 1969b,
1969c; Sealy 1968; Searing 1977).
Phenology
Crested Auklets arrive at their colonies in mid-May,
concurrently with the arrival of Parakeet and Least
Auklets. They begin to occupy the nesting areas
about a week later. Egg-laying begins in mid-June
and continues through the end of June (Searing
1977). On King Island in 1976 and Little Diomede
Island in 1977, egg-laying continued until July,
suggesting that egg-laying may be later in the Bering
Strait colonies (Drury and Steele 1977, Biderman
and Drury 1978). Incubation periods average 35 days
(Sealy 1968). Eggs begin hatching in mid-June and
hatching continues into August (Searing 1977).
Chicks remain in the nest for about 34 days (Sealy
1968) and fledge during the first three weeks of
September.
Productivity
No values of reproductive success for this species
have been published.
Least Auklet (Aethia pusilla)
Distribution
Least Auklets are endemic to the Bering Sea, and
breed on the western Aleutians and the Bering Sea
islands (Udvardy 1963). Their range overlaps with
that of the Crested Auklet, except that they do not
nest as far south (Sealy 1968).
Habitat
Least Auklets nest in crevices in talus slopes and al-
so in the interstices between boulders on boulder
beaches, or occasionally in cracks in cliff faces (Sealy
1968), the same type of nesting habitat as Crested
Auklets use. Competition for nest cracks is mini-
mized by the difference in size between the two
Breeding dL'itribution and reproductive biology 671
species: Least Auklets arc able to use cracks and
crevices which are too small for the Crested Auklets
(Bedard 1969b).
Colonies
Except for those of the Thick-billed Murre (Fig.
39-14), Least Auklet colonies are among the largest in
the Bering Sea (Fig. 39-18); the colonies on Little
Diomede Island, censused in 1977, contained
600,000 Least Auklets. St. George and St. Lawrence
islands also support large numbers. Because of the
difficulties of counting crevice-nesting populations,
the counts of this species represent minimal estimates
and actual numbers may be much higher.
Status of the Bering Sea population
The eastern Bering Sea population of Least Auklets
is estimated to be near 4.5 million (Sowls et al.
1978). The status of this population has yet to be
determined.
Reproductive biology
Least Auklets have been studied on St. Lawrence
Island (Bedard 1967, 1969b, 1969c; Sealy 1968,
1975; Sealy and BMard 1973; Searing 1977).
Phenology
Least Auklets arrive at St. Lawrence Island in mid-
May and occupy nesting areas within a few days.
Laying begins in mid- to late June, depending on
snow conditions, and continues for about three weeks
(Sealy 1968). Eggs are incubated for an average of 31
t
LEAST AUKLET
Colony Si
e
1-100
birds
•
101-1
000 birds
•
1001-
0.000 birds
•
10,00
- 100,000 bird
•
100,00
t- 1.000,000 b
Figure 39-18. Least Auklet colonies in the Bering Sea.
days and begin to hatch in mid-July. Chicks remain
in the nest for about 29 days before fledging. In
1966 and 1967, fledging occurred between 15 Au-
gust and 7 September; mean fledging dates were 1
September in 1966 and 20 August in 1967 (Sealy
1968).
Productivity
On St. Lawrence Island in 1976, reproductive suc-
cess was estimated at 0.34 chicks fledged per nest-
with-eggs (Searing 1977). During 1976 the average
rate of chick growth was 3.7 g/d (Searing 1977). This
compares favorably to the 3.3 g/d rate reported in
1967 (Sealy 1968).
Whiskered Auklet (Aethia pygmaea)
Distribution
Whiskered Auklets are endemic to the Bering Sea
and have the most limited range of the Bering Sea sea-
birds. They breed on the Kamchatka Peninsula and
on the Aleutian Islands from the Islands of the Four
Mountains to the Near Islands (Gabrielson and
Lincoln 1959). This species winters within its breed-
ing range with little indication of southward move-
ment, although individuals have been recorded near
Honshu and Shikohu, Japan (Gabrielson and
Lincoln 1959).
Habitat
Whiskered Auklets are reported to use nesting habi-
tat similar to that used by Least Auklets: cracks and
crevices in talus, boulder beaches, or cliffs
(Gabrielson and Lincoln 1959).
Colonies
Whiskered Auklets are knowm or suspected to nest
on ten of the Aleutian Islands in the central part of
the chain; from Buldir Island east to the Islands of
the Four Mountains and possibly to the Baby Islands
(Sowls et al. 1978). The largest knovioi colony is on
Buldir Island, which has an estimated population of
3,000 (Fig. 39-19). Whiskered Auklets nest in mixed
colonies with Least, Crested, and Parakeet Auklets.
Status of the Bering Sea population
Whiskered Auklets were once more widespread
than they are now (Sowls et al. 1978). Whiskered
Auklets have declined in number or disappeared from
the Near Islands of the Aleutian chain and from the
Komandorsky and Kurile islands (Murie 1959, Sowls
etal. 1978).
Reproductive biology
There is no recent information on the breeding bi-
ology of this species. Buldir Island, which has a large
672 Marine birds
170' 175' 180" 175 i70 165 160' 155" 150'
175' 180° 175 170 165 16tf 155
oSJ-'Pii^^:^ ■*'"
'
iliP^^^^^^ .
i
'1
WHISKERED AUKLET
o''
-
Colony Size
M^^-'
. 1-100 b.rds
• 101-1,000 birds
• 1001-10,000 bitds
W 10,001-100,000 birds
^100,001-1,000.000 birds
▼
^ Unknown number ol birds
•••
HORNED PUFFIN
Colony Si
e
1-100
blfdS
•
101-1
000 birds
•
•
1001-
10,000 birds
10,001
-100,000 birds
•
100,0C
1-1,000.000 birds
▼
Unknc
wn number ot birds
. ♦..
IT
.^^^■
Figure 39-19. Whiskered Auklet colonies in the Bering Sea.
Figure 39-20. Horned Puffin colonies in the Bering Sea.
population of Whiskered Auklets, was studied by U.S.
Fish and WildUfe Service teams but, except for
counts, no information is presently available.
Horned Puffin (Fratercula corniculata)
Distribution
Horned Puffins breed throughout the Bering Sea,
nesting on the Aleutian, Komandorsky, Kurile, and
Bering Sea islands (Gabrielson and Lincoln 1959).
Their breeding range extends north into the Chukchi
Sea and south to Forrester Island in the Gulf of Alas-
ka. Their v^^inter distribution has been reviewed by
Wiensetal. (1978b).
Habitat
Horned Puffins nest in natural rock crevices in
talus, on cliff faces, or in the boulder rubble beneath
cliffs (Sealy 1973, Manuwal and Boersma 1978).
Instances of Horned Puffins digging their own bur-
rows have been recorded (Gabrielson and Lincoln
1959).
Colonies
Horned Puffins nest in association with other
cliff- and crevice-nesting seabirds rather than in
monospecific colonies typical of their congener, the
Common Puffin (F. arctica). Colonies of Horned Puf-
fins generally are made up of fewer than 10,000 birds
(Fig. 39-20). St. George and Little Diomede islands
support the largest aggregations of Horned Puffins.
Status of the Bering Sea population
The population of Homed Puffins in the eastern
Bering Sea is estimated at just under 200,000 (Sowls
et al. 1978). The status of this population has yet to
be determined. However, there are indications that
the numbers of Horned Puffins breeding at the south-
ern limit of their range have declined during this cen-
tury (Heath 1915; Willet 1915; Sowls et al. 1978;
D.H.S. Wehle, University of Alaska, personal com-
munication).
Reproductive biology
The breeding biology of Horned Puffins has been
studied at St. Lawrence Island (Sealy 1973, Searing
1977), the Pribilof Islands (Hunt et al. in prepara-
tion), in Norton Sound (Biderman et al. 1978), and at
the Bering Strait (Biderman and Drury 1978). This
species has also been studied on several of the Aleu-
tian Islands (Wehle 1976) and in the Gulf of Alaska
(Amaral 1977, Leschner and Burrell 1977, Moe and
Day 1977, Wehle et al. 1977, Wehle 1978, Manuwal
and Boersma 1978). These studies are summarized
by Wehle (in preparation).
Phenology
Horned Puffins arrive at their colonies in mid-May
on St. Lawrence Island and the Pribilofs (Sealy
1973, Hunt et al. in preparation) but not until early
June in the northern colonies at Cape Thompson
(Swartz 1966) and the Diomedes (Biderman and
Drury 1978). On St. Lawrence Island and the Prib-
Breeding dislribulion and reproductive biology 673
ilofs, laying apparently begins in mid-June and con-
tinues through early July (Scaly 1973, Hunt ct al. in
preparation). The incubation period averages 40-41
days (Sealy 1973, Amaral 1977). Hatching on the
Pribilofs occurs during the first three weeks of Au-
gust; on St. Lawrence Island, it begins a little earlier
(Sealy 1973, Hunt et al. in preparation). Chicks
fledge after about six weeks in the nest, beginning in
early September (Sealy 1973, Hunt et al. in prepara-
tion, Wehle in preparation).
Productivity
Reproductive success of Horned Puffins varies be-
tween geographical locations and between years
(Table 39-10). Horned Puffins are sensitive to dis-
turbance at the nest, which often results in desertion
(Wehle in preparation). Fledging success is quite high
in Homed Puffins, indicating that most mortality
occurs during the egg stage, due to desertion and
predation.
TABLE 39-10
Estimates of reproductive success of
Horned Puffins in Alaska
No. of
Chicks fledged/
nests
nests
Year
with eggs
with eggs
St. Paul Island,
1975
11
0.45-1.0
Bering Sea
1976
25
0.44
(Hunt et al.
1977
10
0.70-0.78
in preparation
Chowiet Island,
1976
48
0.39
Gulf of Alaska
(Leschner and
Burrell 1977)
Barren Island,
1976
14
0.29
Gulf of Alaska
1977
14
0.64
(Amaral 1977,
Manuwal and
Boersma 1978)
Tufted Puffin (Liinda cirrhata)
Distribution
Tufted Puffins breed throughout the North Pacific,
from Cape Lisbume in the Chukchi Sea south to
Hokkaido, Japan, in the west and southern California
in the east (Sowls et al. 1978). The numerical and
geographical center of Tufted Puffin breeding distri-
bution is in the Aleutian Islands and the northern
Gulf of Alaska (Sowls et al. 1978). Although their
winter distribution is largely unknown, Tufted Puf-
fins are thought to move out of the Bering Sea and
disperse into the oceanic regions of the North Pacific
Ocean (Shuntov 1972).
Habitat
Tufted Puffins nest in burrows excavated in grassy
slopes of fox -free islands or near the tops of cliffs.
They occasionally use unusual nesting habitat such as
closets in grounded ships (Hatch et al. 1979), sandbar
islands (Gill 1978), and rock crevices (Sealy 1973).
Colonies
In the Bering Sea, the availability of suitable nest-
ing habitat free from mammalian predators may be a
limiting factor in the distribution of Tufted Puffin
colonies, although this is not generally true in the
Aleutian Islands (D.H.S. Wehle, personal communica-
tion). The largest colonies (Fig. 39-21) are on Kaliga-
gan Island (375,000 birds) and the Baby Islands
(100,000) (Sowls et al. 1978). Tufted Puffins also
nest in small numbers in grassy areas on cliffs among
other cliff -nesting seabirds.
Status of the Bering Sea population
The eastern Bering Sea population is estimated to
be 1.4 million birds (Sowls et al. 1978). Although
the status of this population is unknown. Tufted Puf-
fins have been declining in numbers in the southern
part of their range. This species formerly nested on
the Channel Islands in California (Howell 1917) but
"^■v:;-
-^ — -^
x^":''"
:■>:
'■■fi'::^:-^'^yM> ' .-:
*.
•
.-■-:■':
iiP^^^^^^^^^^^^^^^^ -
^-%^
s"^
',
▼
:a|
f
*
m
TUFTED PUFFIN
•
Colony Size
. 1-100 birds
■•'->:#
• 101-1,000 birds
• 1001-10.000 Dirfls
# 10 001-100.000 birds
^ too 00 1 - 1.000.000 birds
' 3»-
•
fi
i^ ,
▼ Unknown number of birds
,»'
.;:■»■
Figure 39-21. Tufted Puffin colonies in the Bering Sea.
674 Marine birds
now does not nest south of the Farallon Islands
(Hunt et al. in press). This decline has been attribu-
ted to the combined effects of oil pollution and
depletion of the Pacific sardine (Sardinops sagax)
population (Ainley and Lewis 1974).
Reproductive biology
The breeding biology of Tufted Puffins has not
been studied in the eastern Bering Sea. Several stud-
ies are available for the Aleutian Islands and the Gulf
of Alaska (Dick et al. 1976; Amaral 1977; Baird and
Moe 1978, Leschner and Burrell 1977; Wehle 1976,
1978; Wehle et al. 1977; Manuwal and Boersma 1978;
Nysewander and Hoberg 1978; Hatch et al. 1979;
Nysewander and Barbour 1979).
Phenology
Within the Bering Sea, dates of arrival at several
colonies are known. In the southern Bering Sea, at
Cape Peirce and the Pribilof Islands, Tufted Puffins
arrive on the colonies around 20 May (Petersen and
Sigman 1977, Hunt et al. in preparation). In the
northern Bering Sea, at St. Lawrence and Little Dio-
mede islands, they arrive in late May or early June
(Kenyon and Brooks 1960, Sealy 1973). Studies
from the Aleutians and the Gulf of Alaska provide in-
formation on nesting chronology (Dick et al. 1976;
Wehle 1976, 1978; Amaral 1977; Leschner and Bur-
rell 1977; Wehle et al. 1977; Manuwal and Boersma
1978; Hatch et al. 1979). Breeding appears earUer in
the Gulf of Alaska than in the Bering Sea. In the
Gulf of Alaska colonies, the first eggs were laid
between mid-May and early June. Hatching begins
after approximately 45 days of incubation (Sealy
1973, Amaral 1977). Chicks start to fledge 40 to 45
days after hatching (Nysewander and Barbour 1979).
Productivity
There are no estimates of reproductive success for
Tufted Puffins nesting in the Bering Sea, but it has
been measured at several colonies in the North Pacif-
ic. When disturbance by the observers was minimal,
breeding success in these colonies varied from virtual
failure, 0.009 chicks fledged per egg (Vermeer et al.
1979), to almost complete success, 0.80 chicks
fledged per egg (Nysewander and Hoberg 1978).
There are both regional and yearly fluctuations in
productivity (Wehle in preparation). Several factors
may influence reproductive success: the availability
of food, the amount of predation, and the amount or
frequency of rainy weather, which increases mortaUty
by collapsing or inundating burrows. Although many
burrows are occupied by puffins, only about half
ever receive eggs (Wehle in preparation). There is a
5-15 percent natural desertion rate. Since Tufted
Puffins are very sensitive to disturbance in the egg
stage, observer disturbance increases this rate. Tufted
Puffins, like other puffins (Wehle in preparation),
have a high fledging success; most mortality occurs
during the egg stage.
DISCUSSION
Distribution and numbers
The Bering Sea supports one of the largest aggrega-
tions of seabirds in the world. At least 11.5 million
seabirds have been counted at breeding colonies
(Sowls et al. 1978), and up to 20.5 milUon have been
estimated to breed there. Strikingly, over 95 percent
of the birds counted inhabit colonies with popula-
tions of over a million birds, hereafter referred to as
megacolonies (Fig. 39-23). Megacolonies occur where
abundant nesting habitat coincides with prey popula-
tions sufficient to support large numbers of seabirds.
The species composition of the megacolonies is deter-
mined primarily by the type of food and nesting habi-
tat available. There are two major types of communi-
ties: a talus-nesting community characterized by a
large proportion of zooplanktivorous seabirds, in
which Least and Crested Auklets are the most numer-
ous species; and a cliff -nesting community character-
ized by a large proportion of fish-eating seabirds, in
which murres are the most numerous species (Fig. 39-
23).
The outer shelf colonies, St. Matthew and the Prib-
ilof islands, support over 4.2 million breeding seabirds
(Fig. 39-22, 39-23). The complex oceanic com-
munity along the shelf break and an abundance of di-
verse nesting habitats support these megacolonies. St.
George Island is estimated to support 2.5 million sea-
birds (Hickey and Craighead 1977), making it second
only to St. Lawrence Island. The other colonies (St.
Paul, Otter, Walrus, St. Matthew, Pinnacle, and Hall
islands) have smaller seabird populations.
Twelve species of seabirds breed in the outer shelf
colonies, whereas most of the Bering Sea colonies
have only seven or eight breeding species. The species
composition of the colonies of the Pribilofs and St.
Matthew Island are generally similar. The diets of the
seabird communities in these colonies are not ori-
ented heavily toward either fish or zooplankton con-
sumption: rather there is a fairly equal representa-
tion of both diet types.
The northern colonies (Fig. 39-22, 39-23) support
at least 4.3 million seabirds. The Bering's largest and
third largest colonies aire located in this area; the colo-
nies on St. Lawrence Island harbor 2.7 million sea-
birds and Little Diomede Island supports 1.2 million.
Brccdinfi distrihulion anil rcproducliuc hitjlofiy 675
^^.^.......■^.■.
1
,.„*,j3s-
p;:,,:.:.-^ -r
"":©° -GIl:
MAJOR SEABIRO COLONIES
Moii.icolonioh
o SSSSi
.^,.,.o-*
0 :ss
• '.SSSSSi
o '^^^
0 ■;;..■,
j|v* *•■■;; ■
Figure 39-22. Major seabird colonies in tlie Bering Sea.
The adjacent Big Diomede Island has vast but un-
known numbers of seabirds. These colonies are
less diverse than the outer-shelf colonies; zooplank-
ton-eating seabirds make up at least 88 percent of the
communities.
The seabird colonies on St. Lawrence are concen-
trated on the western end of the island. Although
talus slopes and cliffs are available at the eastern end
of the island, this end supports few seabirds. Those
few that do nest there are fish-eating species typical
of the coastal colonies. The zooplanktivorous Least
Auklets are almost entirely absent. This difference
between the communities of the eastern and western
ends of St. Lawrence Island reflects the different
character of the waters at the two locations. The
eastern end of the island is bathed in Alaska coastal
water, neritic waters strongly influenced by fresh-
water flow from the Yukon River (Coachman et al.
1975). In contrast, the west end of St. Lawrence Is-
land is influenced by currents transporting water and
plankton from deep oceanic waters (T. Kinder,
NORDA, personal communication).
King Island lies 72 km off the mainland between
Norton Sound and Port Clarence. King Island is in-
fluenced by the oceanic currents flowing northward
to the Bering Strait, even though the island lies within
the coastal regime. Consequently, the seabird com-
munities on the island have both "coastal" species
such as Common Murres and Parakeet Auklets and
"oceanic" species like Least and Crested Auklets. Lit-
tle Diomede, the northernmost colony in the Bering
Sea, is dominated by the zooplanktivorous Least and
Crested Auklets. Numbers of murres and kitti wakes
there may be influenced by the lack of cliff-space.
The eastern colonies are a combination of large and
small colonies located in coastal waters and bays of
Bristol Bay and Norton Sound (Fig. 39-22, 39-23).
These colonies sup|)ort cliff-nesting seabird communi-
ties, which appear to be limited by the geographic dis-
tribution of cliff habitat. Large cliffs and colonies are
found at Cape Newenham/Cape Peirce and western
Nunivak Island. The Norton Sound colonies are small
because of the smaller and less predictable fish popu-
lations in the area and the limited distribution of
cliffs. Despite the size differences, the species com-
position of the Norton Sound colonies is similar to
that of the large colonies at Cape Newenham and
Nunivak Island.
The Bristol Bay colonies include Nunivak Island,
Cape Newenham (including Cape Peirce), Bird Rock,
Shaiak, Hagemeister, the Twins, and the Walrus Is-
lands. These colonies are the only large colonies in
coastal waters. Although they encompass a greater
area, their combined seabird population of 2.1 mil-
lion is less that of St. George Island.
The eastern colonies are surrounded by protected
coastal waters which are important spawning and nur-
sery areas for several species of fish. Herring, capelin,
smelt, and salmon are seasonally abundant near the
colonies (Hayes et al., this volume, Straty and Haight
1979). Zooplankton standing stocks in these regions
are low and consist of small species whose maximum
population levels are not reached until late in the
summer (Cooney, this volume). Seabirds that depend
on zooplankton for a substantial part of their diet are
:;:iili--"%^:p-v
■-■.:-:.:,;-:.:.;. >..^/ rrt.«i\ ,
LEAST AUKLETS OOMNA^J'tZ— /
^/ /
"""""
■^y ^■^.-
., A: I-"-- %-^-=-
fcASr&ftfJ COLOMi&S
coMi^tofti fswf^es
"' I
BOKiWA-N'^
j ^4=- i ,
,'\
outer SHeiF COLONIES '
THICK -BILLED MLiRRES -{—
DOMINANT \
BIOGEOGRAPHY:SEABIRO COLONIES
Figure 39-23. Biogeography of seabird colonies in the
Bering Sea.
676 Marine birds
virtually absent from these colonies. These seabird
communities consist mainly of fish-eating species:
Common Murre, Black-legged Kittiwake, and Tufted
Puffin.
Nesting densities are low in these colonies. Com-
pared to the northern and outer shelf colonies there is
more coastal foraging area per bird. There may be
less competition in the waters immediately surround-
ing these colonies than in the other, more densely
populated megacolonies. This reduced density would
benefit inshore foraging species. Compared to the
other megacolonies, the eastern colonies show a
higher proportion of inshore foraging seabirds such as
Pigeon Guillemots and cormorants; the same seems to
apply to eastern St. Lawrence Island.
The Cape Newenham area, which includes sheer
cliffs and predator-free, flat islands, provides a variety
of nesting habitats for seabirds. On Nunivak Island,
the flat areas are preempted by predators, and only
the cliffs on the western end of the island are avail-
able for nesting. The Nunivak Island colonies have
low diversity; Common Murres make up 85 percent
of the colonies. Because of the variety of nesting
habitats in the Cape Newenham area, its population is
more diverse than that of Nunivak Island.
Some species have the majority of their local or
world nesting population concentrated in a few large
colonies, while other species are more evenly distrib-
uted. Red-legged Kittiwakes, Northern Fulmars,
and Whiskered Auklets have the most concentrated
breeding distributions in the Bering Sea. Most of the
Red-legged Kittiwake population nests on St. George
Island, accounting for 88 percent of the world popu-
lation. Northern Fulmars in the Bering Sea are con-
fined to St. Matthew, Chagulak, and the Pribilof is-
lands (Sowls et al. 1978). Over half of the fulmars
breeding in the Bering Sea nest on St. Matthew Is-
land. Whiskered Auklets are known to breed on only
a handful of islands in the central Aleutian chain;
however, their breeding distribution is not well
known. Large numbers of Least and Crested Auklets
also are concentrated on a few islands. The colonies
on St. Lawrence Island support 62 percent of the
Crested Auklet population in the eastern Bering Sea
(Sowls et al. 1978). Least Auklets breeding on St.
Lawrence and Little Diomede islands represent 79
percent of their population in the eastern Bering Sea.
Thick-billed Murres and Black-legged Kittiwakes,
species that are widely distributed in the Bering Sea,
also have a majority of their local populations con-
centrated in single colonies. St. George Island sup-
ports 1.5 million Thick-billed Murres, a substantial
part of the eastern Bering Sea population. The Cape
Newenham colonies are the largest of Black-legged
Kittiwake colonies, and contain more than half of the
eastern Bering Sea population of this species. In
contrast, in the Bering Sea, cormorants, gulls. Para-
keet Auklets, Horned Puffins, and Tufted Puffins are
generally scattered in small colonies.
The biogeography of breeding seabirds reflects
patterns of distribution of suitable nesting habitat
and oceanographic regimes influencing prey avail-
ability (Fig. 39-23). The distribution of seabirds that
are food specialists during all or part of the breeding
season will be largely determined by where their pre-
ferred prey is available. Least Auklets specialize on
Calanus marshallae (= C. finmarchicus) (Bedard
1969c; Hunt et al.. Chapter 38, this volume). These
copepods winter in waters off the continental shelf
and migrate to the surface in late winter or early
spring (B6dard 1969c; R. T. Cooney, University of
Alaska, personal communication). Since the northern
Bering Sea is very shallow, it probably cannot support
indigenous populations of the large copepods (R. T.
Cooney, University of Alaska, personal communica-
tion; F. Favorite, National Marine Fisheries Center,
personal communication; H. Feder, University of
Alaska, personal communication). It appears, but
remains to be tested, that the large Least Auklet
colonies in this area depend upon copepods carried
by currents that flow from the deep Aleutian Basin,
along the western side of St. Lawrence Island and
northeast into the Bering Strait (T. Kinder, personal
communication). Although this mass of outer shelf
water and its associated copepods are carried north
into the Chukchi Sea and beyond, the late arrival
of these copepods in these far northern waters
prevents Least Auklets from foraging extensively or
breeding north of the Bering Strait. We conclude
that Least Auklets are limited to breeding on islands
near water masses which contain these large copepods
in abundance in early summer.
Other seabirds whose breeding distributions closely
follow the distribution of their prey are the Red-
legged Kittiwake and the Northern Fulmar. In the
Bering Sea, both of these species concentrate their
foraging near the shelf break (Hunt et al.. Chapter 38,
this volume). The Red-legged Kittiwake is a pelagic
gull that specializes on myctophids (Hunt et al..
Chapter 38, this volume), a family of deep-water fish.
Red-legged Kittiwake colonies are found only on is-
lands near the continental slope. The proximity of
these islands to the shelf break insures the availability
of these deepwater organisms.
Northern Fulmars are generalized oceanic scaven-
gers (Ainley and Sanger 1979). On the Pribilof Is-
lands, food studies based on a small sample revealed a
diet of cephalopods and walleye pollock (Hunt et al.
Breeding distribution and reproductive biology 677
Chapter 38, this volume). Whether fulmars are scav-
engers, fish-eaters, or heavy users of cephalopods,
the shelf break provides access to all three food types.
In the Bering Sea, Northern Fulmars are limited
to nesting on islands near the shelf break, although
their extended foraging range allows them to nest on
more distant islands, such as St. Matthew, than can be
used by Red-legged Kittiwakes.
The breeding distribution in the Bering Sea of
murres and Black-legged Kittiwakes, the primary
components of cliff-nesting communities, appears to
be limited by the availability of nesting habitat. These
species feed primarily on fish, which are seasonally
abundant throughout the southeastern Bering Sea.
Since their prey is widespread, these birds are able to
use nesting habitat wherever it occurs. Cliffs are prev-
alent on volcanic islands such as St. Matthew, west-
em St. Lawrence, and the Pribilofs, but compara-
tively rare on the mainland of the Bering Sea coast,
occurring at Cape Newenham, Cape Vancouver,
Cape Denbigh, and Cape Darby.
While the distribution of cliffs limits the distribu-
tion of cUff-nesting seabirds as a group, the composi-
tion of the cliff colonies may be influenced by the
type and abundance of prey available in the adjacent
waters. Common and Thick-billed Murres occur to-
gether in most of the Bering Sea colonies. However,
one species usually predominates over the other. In
the coastal cliff communities, Common Murres are
the dominant species, often composing as much as 95
percent of the colony. The outer shelf colonies are
dominated by Thick-billed Murres (Figs. 39-12, 39-
13,39-23).
Differences in the diets of the two species of
murres may account for this distribution pattern.
Common Murres depend primarily on fish, while
Thick-billed Murres take a considerable amount of
zooplankton in addition to fish (Tuck 1960; Swartz
1966; Spring 1971; Hunt et al. Chapter 38, this
volume). The absence of Thick-billed Murres and
plankton-eating auklets from the eastern colonies
may be the result of the lack of large species of zoo-
plankton in coastal waters in sufficient abundance
early enough in the summer to support breeding.
Access by mammalian predators to nest sites may
limit the local breeding distribution of seabirds.
Predation is most devastating for ground-nesting spe-
cies such as terns, large gulls, and Tufted Puffins.
River otter (Lutra canadensis) and Arctic fox (Alopex
lagopus) predation have caused terns and Tufted Puf-
fins to abandon colonies in the Gulf of Alaska (Baird
et al. 1979). In cliff colonies, foxes constantly take
seabirds nesting in accessible areas.
Reproductive ecology and variability
The productivity of Bering Sea marine birds varies
among colonies, and for some species in some areas,
reproductive success may change dramatically from
one year to the next. Comparisons of productivity
between colonies within the Bering Sea and with
populations elsewhere in the world can provide clues
to the key factors determining reproductive success
and the long-term trends of populations.
In the eastern Bering Sea, the two species of kitti-
wakes, which are limited to foraging at the surface,
appear to have greater yearly variations in reproduc-
tive success (Table 39-6) than diving seabirds, such as
the murres, within the same colonies (Tables 39-8 and
39-9). We hypothesize that the greater variation in
reproductive success of kittiwakes is the result of the
variable availability of the foods concentrated near
the ocean's surface. Surface-foragers will be unsuc-
cessful if storms or rough seas interfere with prey cap-
ture or if prey fail to concentrate near the surface, al-
though moderate wind speeds may improve fishing
(Dunn 1973). In contrast, diving birds may forage
throughout the water column, thereby lessening their
vulnerability to surface conditions unfavorable for
foraging, or their dependence upon surface swarming
of prey. Although severe storm conditions are also
known to affect diving birds (Bailey and Davenport
1972, Birkhead 1976, Vermeer et al. 1979), repro-
ductive losses of kittiwakes in the Bering Sea have
been tied to storms (Braun in preparation. Hunt
et al. in preparation), and we expect these surface
foragers to be more sensitive to rough seas during
critical periods in the breeding cycle than the diving
species (Ainley 1977). Storms are more frequent in
the southern Bering Sea than in the north (Niebauer,
Chapter 3, Volume 1), and the poor weather of the
southern region may limit the reproductive success
achieved by some species.
Weather can also influence reproductive success of
seabirds by directly affecting prey populations (Las-
ker, in press). The recruitment of large numbers of
young walleye pollock depends on the incidence of a
few storm-free days in April or May which allow new-
ly hatched pollock fry to become established (Coon-
ey et al. 1978). Storms during this period may
reduce the number of young-of-the-year pollock
which are an important part of the diets of kittiwakes
and murres (Hunt et al., Chapter 38, this volume).
The limit of the ice-edge, dependent on weather (Nie-
bauer, Chapter 3, this volume) and a determinant of
sea temperatures, can affect where fish spawn (Favor-
ite et al. 1977). Major spawning areas for capelin
occur near the colonies at Cape Newenham (Barton et
al. 1977), and a significant shift in spawning location
678 Marine birds
north or south could render this food resource in-
accessible to seabirds nesting in these colonies.
The constancy of reproductive success in seabirds
reflects the abundance and availability of their prey
populations. Prey is not distributed evenly through-
out the Bering Sea. Fish resources are great in the
southern Bering Sea. This region supports a large
commercial fishery, and the continental shelf be-
tween the Pribilof Islands and Bristol Bay is a nursery
area for v^^alleye pollock and salmon (Cooney et al.
1978, Straty, Chapter 35, Volume 1). The surface-
foraging young of salmon and walleye pollock are im-
portant resources for seabirds (Ogi and Tsuijita 1973,
Hunt et al.. Chapter 38). In addition, Bristol Bay is a
spawning area for many fish species (Barton et al.
1977). At the shelf edge, zooplankton diversity
increases and biomass reaches a maximum (Motoda
and Minoda 1974). In the northern Bering Sea,
resident commercial fish populations may be smaller
due to sub-zero sea temperatures (Alton 1974).
However, bait fish which migrate into the area may
be locally abundant.
Variability in reproductive success of the Black-
legged Kittiwake is much greater in Norton Sound
than in the Pribilof Island colonies, reflecting regional
differences in the food resources on which the local
populations depend. Seabirds breeding at the Prib-
ilofs have access to a wide variety of foods, and when
one prey item is not available, there may be alternate
prey. The Norton Sound kittiwake colonies are de-
pendent on schools of fish migrating into foraging
areas close to the colonies. In years when fish are
readily available, these colonies are the most produc-
tive in the Bering Sea, but in other years they may
completely fail to produce young. During our studies,
average productivity was very low in the Norton
Sound colonies. Colonies with stable, moderate levels
of productivity may export young and play a dispro-
portionately great role in sustaining Bering Sea kitti-
wake populations.
Comparisons of the reproductive biology of marine
birds in the Bering Sea with that of populations of
the same species elsewhere suggest that the Bering Sea
populations may have greater difficulty in obtaining
the food required to sustain reproduction. In the
Bering Sea, Pelagic Cormorants, Glaucous-winged
Gulls, and Black-legged Kittiwakes lay smaller
clutches and produce chicks with slower growth rates
than populations breeding in other areas. Reductions
of clutch size and growth rates have been related to
reduced energy intake with relation to need (Perrins
1965, Lack 1968, Hunt and Hunt 1976).
Reduction of reproductive success related to ener-
getics may arise when resources become less available,
or when environmental conditions cause the energetic
costs of survival to rise. In the Bering Sea, both
causes appear to be acting. Existence in the lower
temperatures of the Bering Sea may be more costly
than in the warmer North Atlantic and North Pacific.
The inclement weather of the southern Bering Sea
may place an energy drain on young birds attempting
to maintain normal body temperatures in the cold
winds and rain. Moreover, Bering Sea colonies are
generally much larger than colonies in the North
Pacific or North Atlantic (Cramp et al. 1974, Sowls et
al. 1978, Manuwal and Campbell 1979). Competi-
tion, either through interference or by lowering prey
populations, could reduce the availability of food
near large colonies for some species (Hunt et al. in
preparation). If fluctuations in prey populations
caused by other oceanographic conditions are added,
occasional severe shortages of food, such as appear to
occur in the eastern colonies, are probable.
The diets of murres and Black-legged Kittiwakes
show considerable overlap (Hunt et al.. Chapter 38,
this volume). There is evidence that competition be-
tween these species may influence the availability of
food for Black-legged Kittiwakes. In the Barents Sea,
kittiwakes laid smaller clutches and fledged fewer
young in years when murre populations at their colo-
nies were high (Belopolskii 1957). Belopolskii sug-
gests that when competition between murres and
kittiwakes is severe, kittiwakes may be forced to
switch to an alternate prey with a lower nutritional
value, such as crustaceans, which may result in low-
ered productivity.
In the Bering Sea, two types of evidence suggest
that seabirds in the megacolonies may be under com-
petitive stress for food. First, we find a consistent
difference between Black-legged Kittiwakes and
Thick-billed Murres on St. Paul and St. George
islands in growth rates and productivity as well as
in fledging weights of murre chicks. On St. Paul,
growth rates, productivity, and murre fledging
weights are slightly, but consistently, higher. St. Paul
Island, which lies 74 km northwest of St. George,
supports a population an order of magnitude smaller
than that on St. George Island, due to limited nesting
habitat. Thus, on St. Paul Island there are fewer
birds competing for food, pairticularly in the inshore
waters, where the capture of prey demands less
long-distance commuting.
A second line of evidence suggests that competi-
tion in the inshore waters may be greater in the dense
colonies of St. George Island thcin in the smaller colo-
nies at Cape Newenham, which are spread over a
greater length of shoreline. Obligate inshore-foraging
Breeding duilrihulion and reproductive biology 679
species such as the cormorants and the Pigeon Guille-
mot are common at Cape Newenham and relatively
uncommon or, like the guillemot, not present at St.
George. A possible explanation of this difference,
based on our experience in the Pribilofs, is that the
great numbers of murres at St. George, which occa-
sionally take inshore fish (Hunt et al. in preparation),
competitively exclude or depress the population of
inshore specialists because of their great numbers and
ability to use alternate foods while cropping local
resources on which inshore foragers depend. How-
ever, Drury (personal observations) has found large
numbers of guillemots associated with murres in the
Bering Strait and the above hypothesis apparently
does not help with understanding distributions in the
northern colonies, where murre populations are
smaller.
Finally, surface-feeding seabirds have two ways of
coping with fluctuating food supplies. The first is il-
lustrated by Black-legged Kittiwakes, which use a
behavior that allows them to maximize the number of
young they produce under both favorable and stress-
ful conditions. In the Bering Sea, they lay two eggs
and, when conditions permit, produce more young
per nest than the diving seabirds. Under less favor-
able conditions, the older chicks of Black-legged
Kittiwakes eliminate their younger siblings within a
few days of hatching. Under very poor conditions,
kittiwakes may fail entirely to lay eggs, but occa-
sional failure is not permanently damaging to their
populations because they can make up for losses
in a good year.
A second mechanism for dealing with short-term
fluctuations in food supply is illustrated by the Pro-
cellariiformes. Given a longer breeding season, sur-
face-feeding seabirds can overcome temporary inter-
ruptions in food availability by having young with
low growth rates and the ability to store fat. The
Procellariiformes combine these adaptations with a
long foraging range, the ability to feed their young on
secretions, and eggs and young that can tolerate peri-
ods of neglect (Boersma and Wheelwright 1979). In
the southern Bering Sea, Northern Fulmars are among
the first to lay eggs and the last to fledge young. It is
not known why fulmars and storm-petrels do not
breed in the northern Bering Sea.
The different reproductive patterns of seabirds be-
come important when adult mortality increases, as
after an oil spill. The alcids lay a single egg and
would require a long time for population recovery
(Wiens et al. 1978a), since the maiximum number of
young a pair could raise in a year is one. Kittiwakes
and other seabirds which lay multiple-egg clutches
have the potential for more rapid population re-
growth and could recover more quickly given ade-
quate food and optimal environmental conditions.
Where food supplies are inadequate, however, it is un-
likely that kittiwake populations would recover more
quickly than those of alcids.
SUMMARY
The Bering Sea is one of the richest and most im-
portant breeding areas for seabirds in the world. Most
birds are concentrated in a very few colonies— gener-
ally large communities of cliff-nesting species in the
south and talus-nesting species in the north. Diving
seabirds predominate and have relatively stable levels
of productivity. The unpredictable vdnds and turbid
seas in these northern waters may put surface-feeding
seabirds at a disadvantage. In contrast to the diving
seabirds, some of the surface-feeding seabirds fluctu-
ate widely in reproductive success from year to year.
These species generally lay multiple egg clutches and
are able to capitalize on occasional good years to
maintain population stability or growth.
ACKNOWLEDGMENTS
Many research groups contributed to the work pre-
sented here. We thank the many field assistants, too
numerous to name individually, who aided in these
studies of Bering Sea marine birds. We especially
wish to acknowledge the efforts of A.L. Sowls, S.A.
Hatch, C.J. Lensink, and others in compiling the
Catalog of Alaskan Seabird Colonies, without which
the task of v^iting this chapter would have been
impossible. We thank the many people who have
shared their ideas and data with us, including P.A.
Baird, L.K. Coachman, R.T. Cooney, F. Favorite, H.
Feder, P. Gould, J. Hickey, T.H. Kinder, J.D. Schu-
macher, and D.H.S. Wehle. We are grateful to Molly
Warner for aid in the field and to the National Marine
Fisheries Service on the Pribilof Islands for housing
and logistic support. We thank P. Baird, B. Braun, M.
Dick, S. Hatch, D. Nysewander, D. Wehle, and partic-
ularly C. Ramsdell for valuable suggestions for im-
proving the manuscript. We particularly wish to
thank Lucia Schnebelt and Tana Forstrom for their
infinite patience and perseverance in preparing this
manuscript.
This study was supported by the Bureau of Land
Management through interagency agreement with the
National Oceanographic and Atmospheric Adminis-
tration, under which a multiyear program responding
to needs of petroleum development of the Alaskan
continental shelf is managed by the Outer Continen-
tal Shelf Environmental Assessment Program
(OCSEAP) office.
680 Marine birds
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Pelag'ic Distribution of Marine Birds
in the Eastern Bering Sea
George L. Hunt, Jr.,' Patrick J. Gould,^
Douglas J. Forsell," and Harold Peterson, Jr?
'Department of Ecology and Evolutionary Biology
University of California, Irvine
' Biological Services Program
United States Fish and Wildlife Service
Anchorage, Alaska
^Department of Qiemistry
University of Rhode Island
Kingston, Rhode Island
ABSTRACT
Analyses of the most abundant marine bird species in the
eastern Bering Sea indicate that their distribution and abun-
dance are the result of complex interactions between biotic
and abiotic elements of the environment. Of particular impor-
tance are the effects of ice systems, food availability, oceano-
graphic frontal systems, and the location of suitable nesting
sites. For most species, the southern ice edge acts as a barrier
to northward movement in the spring. OCSEAP surveys indi-
cate that previous estimates of seabird populations in the
Bering Sea are probably extremely conservative and that more
than 40 million seabirds may occupy these marine waters
during the summer months.
INTRODUCTION
Seabirds, the most visible element of the marine
fauna, make their living from the sea and spend most
of their lives away from land. Their pelagic distribu-
tion is linked to the distribution of the resources on
which they depend. Thus, variations in distributions
of seabirds may reflect differences in the availability
of preferred prey or differences in oceanographic
parameters which affect the availability of those prey.
This chapter summarizes our current knowledge of
the distribution and abundance of marine birds in the
waters of the eastern Bering Sea.
Brown (1980) reviewed past studies of the pe-
lagic distribution of seabirds. Many of these records
lacked a quantitative base and were restricted to
sightings made from vessels plying the shipping lanes.
Later, quantitative data gathered from research ves-
sels not only expanded our understanding of distribu-
tion, but also provided the means of integrating data
on seabirds and their marine environment. Bourne
(1963), Ashmole (1971), and Nelson (1970, 1978)
have reviewed much of this early work.
Large-scale regional differences in productivity or
sea-surface temperature long have been recognized as
important correlates of changes in seabird distribu-
tion or numbers (Jesperson 1924, 1930; Haegerup
1926; Wynne-Edwards 1935; Murphy 1936; Kuroda
1955, 1960; Salomonsen 1965; Bailey 1968; King
and Pyle 1957; Gould 1971, 1974; Shuntov 1972;
Jehl 1974; King 1974; Sanger 1974; Brown 1979;
Pocklington 1979). More recently, investigations of
restricted areas have provided additional insights
about factors affecting local seabird distribution
(Uspenski 1958, Swartz 1967, Bartonek and Gibson
1972, Brown et al. 1975, Wiens and Scott 1975,
Brovm 1980, Ainley 1976, Baltz and Moorejohn
1977, Nettleship and Gaston 1978, Wahl 1978,
Iverson et al. in press). Local phenomena that may
result in concentrations of birds include concentra-
tions of food, marine predators, tidal eddies, and
convergence and divergence fronts (Brovm 1980).
The importance of convergence fronts in concen-
trating marine organisms consumed by birds in the
English Channel has been discussed by Pingree et al.
(1974). The role of both convergence and divergence
fronts for seabirds has been stressed by Murphy
(1936), King and Pyle (1957), Ashmole and Ashmole
689
690 Marine birds
(1967), Gould (1971), and Brown (1980). Brown
describes a front at the outer edge of the Labrador
current at which concentrations of Greater Shear-
waters (Puffinus gravis). Northern Fulmars (Ful-
marus glacialis), and Black-legged Kitti wakes (Rissa
tridactyla) forage. On a smaller scale, he describes
neuston-foraging birds using concentrations of food
in the convergences associated with wind-driven
Langmuir circulation cells.
Ashmole and Ashmole (1967) were limited to a
colony-based study, but they hypothesized that
localized concentrations of plankton and nekton pro-
duced by convergence and sinking of surface waters at
"fronts," which have been suggested as exerting impor-
tant effects on the distribution of surface schools of
tunas in the open ocean, may also provide favorable
feeding grounds for many oceanic birds.
Gould (1971) refined this concept in his work in
the eastern tropical Pacific. He found that larger,
nekton-feeding birds were most numerous in areas
of convergence, while smaller, plankton-feeding birds
were most numerous in areas of divergence and up-
welling.
At the other end of the scale, Cody (1973), Bedard
(1967, 1969, 1976), Scott (1973), Hamner and
Hauri (1977), Nettleship and Gaston (1978), Hunt
(1976, 1977), and Hunt et al. (1978, in preparation)
have investigated the foraging ecology and pelagic
distribution of breeding seabirds in the vicinity of
nesting colonies. Hamner and Hauri (1977) and
Ingham and Mahnken (1966), working in the tropics,
found that birds congregate downstream from islands
at plankton-concentrating eddies caused by tidal or
oceanic currents. Bedard, working at St. Lawrence
Island, emphasized that concentrations of food in
areas of tidal mixing resulted in large aggregations of
multispecies groups of plankton -eating auklets. In
contrast, Cody believed that alcids in Iceland and the
eastern North Pacific generally foraged in discrete
zones at varying distances from colonies according to
the energetic requirements of each species. Hunt and
associates have found in some circumstances a partial
zonation by distance from colony, and in others
clumping in food-rich areas.
THE BERING SEA
The physical and biological oceanography of the
eastern Bering Sea shelf are well described elsewhere
in these volumes. Features of principal importance
for understanding the marine ornithology of the
region include: (1) seasonal ice development and its
I
effects on the marine biota, (2) a broad, shallow
continental shelf that drops off precipitously into a
deep basin, (3) a scattering of rocky cliffs and head-
lands along the mainland shore and on several islands
wdthin reasonable proximity to the shelf break, and
(4) a series of frontal systems approximately parallel
to and at the 200, 100, and 50-m isobaths. As
described in Volume 2, Section X, at each of these
fronts changes in nutrient cycling or in structured
aspects of the planktonic community result in
changes in the community of organisms at a higher
trophic level.
The relationship between the distribution of ma-
rine birds in the northern North Pacific Ocean /Bering
Sea and the oceanographic features of these waters
has been studied in recent years. Kuroda (1960) at-
tempted to correlate numbers of seabirds with food
availability and sea-surface temperatures, and Shun-
tov (1972) stressed the importance of up welling near
the shelf break and the higher productivity of shelf
waters in concentrating foraging seabirds. In the
North Pacific, the confluence of the cold Oyashio and
warm Kuroshio currents was identified by Wahl
(1978) as an area rich in seabirds. Swartz (1967) dis-
cussed bird distributions in the Chukchi Sea and
Bering Strait regions. Most recently, Iverson et al.
(1979) have shown that seabird densities over the
southeastern Bering Sea shelf are related to frontal
systems along the continental slope near the shelf-
break at the 200-m isobath, and shoreward to a mid-
dle shelf front, near the 100-m isobath. In a series of
cruises, bird densities were found to be high from
near the shelf break shoreward to the 100-m isobath,
but considerably lower over shallower waters.
Prior to the Outer Continental Shelf Environmen-
tal Assessment Program (OCSEAP) cruises, knowl-
edge of the pelagic distribution of seabirds over the
eastern Bering Sea shelf was limited. Irving et al.
(1970), Bartonek and Gibson (1972), and Wahl
(1978) reported on birds which spent only brief
periods on shelf waters, seen in the course of single
cruises made for other purposes. Wahl found a
marked change in the density of birds and their spec-
ies composition as he crossed from deep oceanic wa-
ters over the shelf break. In particular, storm-petrels
were less common over the shelf, while murres and
Short-tailed Sheairwaters (Puffinus tenuirostris) in-
creased in density. He also saw several Mottled
Petrels (Pterodroma inexpecta) over the deep oceanic
waters, but none over the shallower shelf. Wahl
estimated a density of 3.9 birds per km^ for all
species combined over the oceanic waters, compared
to 14.9/km^ for the shelf area. These values are com-
parable to those obtained by Shuntov (1972) of
Pelagic (I is I rib ulion 691
2.7/km^ and 18/km\ respectively. Sanger (1972)
also provided estimates of pelagic bird density over
the Bering Sea shelf and oceanic basin, but his figures
were based on extrapolations from other areas.
Recently, Sowls et al. (1978) estimated that there
are about 25.3 million seabirds associated vi^ith
local breeding colonies in the summer.
Bay, continental shelf, and shelf-break waters
amount to about 807,000 km^ of surface area in the
eastern Bering Sea. According to data from Sowls et
al. (1978), this represents about 0.03 km^ of avail-
able foraging habitat per bird, or 31.5 birds per km^
of habitat. If we assume that 40 percent of these
birds are occupied at colonies at any given time, a
reasonable figure as indicated by our studies of
breeding biology in Alaskan waters, we then have
about 18.8 birds per km' over the ocean at any one
time. Add to this a minimum of 9 million nonbreed-
ing shearwaters and at least several million non-
colonial breeding birds, and we can conservatively
expect a density of 32 birds per km'' in the eastern
Bering Sea/Aleutian Islands area during the breeding
season. This density translates to about 26 million
birds, considerably more than Shuntov's (1972) esti-
mate of 23.8 million for the entire Bering Sea. Den-
sities derived from the survey data discussed in the
present report indicate that 26 million is a conser-
vative estimate.
METHODS
We summarize information on the pelagic distribu-
tion of seabirds in the eastern Bering Sea obtained by
numerous investigators as part of the OCSEAP study
in 1975-78. For abundant species, we provide a brief
introduction summarizing trophic biology and nesting
colony preferences, two features that strongly influ-
ence pelagic distribution. Within seasons, we show
differences in the distributions of various species or
species groups, and within species, we show seasonal
changes in distribution and abundance. When possi-
ble these variations in distribution and abundance are
related to nesting habitat, food resources, and marine
conditions. Species that do not occur in large num-
bers are covered briefly.
Aerial transects were made from several kinds of
fixed-wing aircraft and helicopters. Most shipboard
surveys were conducted from research ships in the
National Oceanographic and Atmospheric Admin-
istration (NOAA) fleet, or vessels chartered by
OCSEAP. Thus, visibility and working conditions
were not standardized for all transects.
Methods of census were partially standardized, but
did vary somewhat between investigators and be-
tween platforms. In general, aerial surveys were
flown at altitudes between 30 and 50 m at speeds
from 75 to 150 kn, depending upon the aircraft
used. Each transect segment then consisted of a path
of fixed width (often 50-150 m), within which all
birds seen were recorded for some fixed time or dis-
tance. Shipboard surveys were generally conducted
in time segments (= transects) of 10-15 min at speeds
of 10-13 kn. During each transect, all birds from
ahead of the vessel to 90° on whichever side afforded
the best visibility were recorded to a distance of 300
m. Some investigators varied transect widths or at-
tempted to compensate for the movement of flying
birds relative to the transect path. For the purposes
of the present review, bird densities (birds /km^) ob-
tained by these slightly differing methods are all
treated together.
Data from shipboard and aerial surveys are com-
bined for species distributions when visual inspection
of separate mappings of shipboard and aerial survey
data suggested that conclusions to be drawn from the
two data sets were similar. When striking differences
occurred (Northern Fulmar) or one method was in-
appropriate (Red-legged Kittiwake), data from the
two survey methods are presented separately. The
rationale for the method of presenting data is given
under the discussion of each species.
Observations were divided into four categories by
season: March-May (spring); June-August (summer);
September-November (fall); and December-February
(winter). Survey coverage for each season is given in
Figs. 40-1 to 40-8. Summer data are the easiest to in-
terpret and most numerous. Fall data are compli-
cated by migratory behavior, and spring data are in-
ordinately affected by ice coverage and ice-edge
phenomena. Winter data are exceptionally sparse.
Within each season, all transect segments within each
30 minutes of latitude and 60 minutes of longitude
were averaged to provide a mean density for that
block in that season. Population estimates were de-
rived solely from survey data collected by the U.S.
Fish and Wildlife Service, Biological Services Program,
and are based on 523,232 km" of continental shelf,
248,242 km^ of shelf break, and 648,341 km' of
oceanic surface area in the Bering Sea east of the
U.S. -Russia convention line of 1867.
RESULTS
About 45 species of seabirds (excluding loons,
grebes, waterfowl, and shorebirds) occur regularly in
the Bering Sea/Aleutian Islands ai-ea of Alaska. Of
692 Marine birds
Figure 40-1. Survey effort— ship transects: March-May
1975-78. Numbers indicate the transects completed in each
area.
Figure 40-2. Survey effort— air transects: March-May
1975-78. Numbers indicate the transects completed in each
area.
175° 170° 165
Figure 40-3. Survey effort— ship transects: June-August
1975-78. Numbers indicate the transects completed in each
area.
Figure 40-4. Survey effort— air transects: June-August
1975-78. Numbers indicate the transects completed in each
area.
Pe logic d is I rib ution 693
Figure 40-5. Survey effort— ship transects: September-No-
vember 1975-78. Numbers indicate the transects com-
pleted in each area.
Figure 40-6. Survey effort— air transects: September-
November 1975-78.
Figure 40-7. Survey effort— ship transects: December-
February 1975-78.
Figure 40-8. Survey effort— air transects: December-
February 1975-78."
694 Marine birds
these, 20 percent are nonbreeding visitors, and two
species, Whiskered Auklet and Red-legged Kittiwake,
are essentially endemic to the area. Populations of
twelve species exceed one million: from the highest
to lowest, Short-tailed Shearwater, Least Auklet,
Thick-billed Murre, Common Murre, Fork-tailed
Storm -Petrel, Leach's Storm-Petrel, Crested Auklet,
Tufted Puffin, Northern Fulmar, Black-legged Kitti-
wake, and Sooty Shearwater.
Albatross (Diomedea spp.)
Three species of albatross have been recorded in
the Bering Sea as nonbreeding visitors (May-October).
Short-tailed Albatross (D. albatrus) are extemely rare
and have been designated an endangered species.
Black-footed Albatross (D. nigripes) are fairly com-
mon in the vicinity of the Aleutian Islands but rare
elsewhere in the Bering Sea. Laysan Albatross (D. im-
mutabilis) are fairly common over shelf-break and
oceanic waters north to about 55° N, especially in
western areas. On occasion albatross may follow
ships into shelf waters, especially through Unimak
Pass, but such records are few.
Northern Fulmar (Fulmarus glacialis)
The Northern Fulmar is the only species of the
family Procellariidae that breeds in Alaska. In the en-
tire Alaskan cirea there aire 12 more or less distinct
colonies, 4 of which account for more than 99 per-
cent of the population. Two are in the eastern Bering
Sea (77,000 on St. George Island and 450,000 on St.
Matthew and Hall islands), and one is in the central
Aleutians (450,000 on Chagulak Island); the fourth is
composed of 475,000 birds on the Semidi Islands in
the Gulf of Alaska. These birds nest on cliff ledges
and may forage at long distances from nesting sites
(Fisher 1952, Hatch 1978). Sowls et al. (1978) esti-
mated that about 1.3 million fulmars are associated
with breeding colonies in the eastern Bering Sea/
Aleutian Islands area. Shuntov's (1972) data indi-
cated a pelagic population of nearly 3 million in the
entire Bering Sea.
Fulmars forage on a variety of fish and squid, as
well as offal from fishing vessels (Hatch 1978, Wahl
and Heinemann 1979). They obtain this food at or
very close to the ocean's surface, either by sitting on
the surface and pecking at items, or by plunging from
< 1 m above the surface.
Shuntov (1972) showed fulmars to be abundant
over all ice-free waters in the Bering Sea throughout
the year. He said that they were most dense in waters
off Kamchatka and the Komandorsky and Aleutian
islands, as well as over the shelfbreak from the Aleu-
tians north to the Chukchi Peninsula. He reported
very low numbers in the shallower waters of the east-
ern Bering Sea such as Norton Sound and Bristol Bay.
Fulmars are attracted to ships and, unless great
care is taken, ship-foUovdng birds cause the number
of birds recorded to be greatly exaggerated. For ful-
mars in the Bering Sea, it is likely that aerial surveys
provide the best estimate of .density. Hunt et al.
(1978) conducted helicopter surveys in conjunction
with shipboard observations. In the vicinity of the
shelf break, where the fishing fleets commonly oper-
ate, fulmars formed a halo of concentration out to a
mile or more from a non-fishing research vessel even
though it was providing no food rewards. These
haloes of birds were hard for shipboard observers to
distinguish from areas of naturally occurring high
density, but their true nature was obvious from the
air. Although we lack adequate quantified data from
simultaneous helicopter and ship operations in other
areas, it is our impression that fulmars follow non-
fishing research vessels more regularly in those por-
tions of the Bering Sea frequented by fishing vessels
than in other Alaskan waters. We present here den-
sity distributions based on aerial and shipboard sur-
veys. The latter have been included because they pro-
vide comparison wdth other shipboard surveys and
because they also demonstrate diagrammatically the
patterns of pelagic distribution of fulmars.
The pelagic distribution of Northern Fulmars is
given in Figs. 40-9 to 40-14. Fulmars were found
throughout ice-free areas of the eastern Bering Sea in
spring, summer, and fall. The majority of birds oc-
curred over the shelfbreak, as is true also in the Gulf
of Alaska (Hunt and Briggs 1975). Very few were
found in the northern Bering Sea (see Swartz 1967)
or in the shallow waters of Norton Sound and Bristol
Bay. Bartonek and Gibson (1972) reported higher
concentrations of fulmars within Bristol Bay than we
generally found.
There is a major fishery for walleye pollock (Ther-
agra chalcogramma) along the shelf-break area be-
tween the Pribilof Islands and Unimak Pass, where
fulmars frequently congregate in immense flocks
around fishing vessels and factory ships. Thus, al-
though the shipboard surveys, and to a lesser extent
the aerial surveys, showed fulmars concentrated along
the shelf break, it is possible that they were there be-
cause offal from fishing vessels was plentiful rather
than because natural foods are concentrated there. At
present, we know too little about their preferences
for natural foods and their distribution in the absence
of fishing vessels to speculate on what their "natural"
distribution in the Bering Sea might be.
Our impressions of the relative abundance of light-
and dark-phase fulmars are in general agreement
\
175° 170'
Figure 40-9. Pelagic distribution of Northern Fulmars— siiip
surveys: Marcii-May.
Figure 40-10. Pelagic distribution of Northern Fulmars— air
surveys: March -May.
155°
Figure 40-11. Pelagic distribution of Northern Fulmars— Figure 40-12. Pelagic distribution of Northern Fulmars— air
ship surveys: June-August. surveys: June-August.
695
696 Marine birds
175° 1 ro-
les"
Figure 40-13. Pelagic distribution of Northern Fulmars-
ship surveys: September-November.
Figure 40-14. Pelagic distribution of Northern Fulmars— air
surveys: September-November.
with Shuritov (1972). Hunt et al. (1978) found that
light birds predominated north of the Pribilofs, and
dark-phase birds predominated south of these islands.
Shuntov's (1972) Fig. 19 shows that few or no dark-
phase birds were found north of the Aleutian chain in
the eastern Bering Sea in summer. In the text, how-
ever, he suggests that in June and July, 35 to 70 per-
cent of the birds along the shelf break may be dark-
phase birds. In winter, according to Shuntov, both
light- and dark-phase birds were displaced to the
south, as many birds leave the Bering Sea.
Density estimates from our aerial surveys indicated
a pelagic population of about 2.1 million fulmars in
summer, and much higher numbers in the fall. The
fall estimates, however, were greatly inflated due to
several very large aggregations encountered over the
shelf break. This figure exceeded the 1.3 million
birds estimated by Sowls et al. (1978) from colony
counts; it may reflect the incursion into the Bering
Sea of birds from colonies elsewhere and certainly in-
cludes additional nonbreeding birds.
Shearwaters (Puffinus sp.)
Flesh-footed Shearwaters (P. carneipes) are occa-
sional nonbreeding visitors (May-September) to the
southeastern continental shelf of the Bering Sea.
Short-tailed and Sooty Shearwaters (Puffinus ten-
uirostris and P. griseus)
Both Short-tailed and Sooty Shearwaters occur in
the Bering Sea, with Short-tailed Shearwaters greatly
predominating. Since these species are often difficult
to distinguish in the field, many field investigators did
not attempt to separate them and data from both spe-
cies are combined in this account. Both species nest
in the southern hemisphere and part of their popula-
tions spend the austral winter in the north. Shuntov
(1972) estimated that about 8.7 million shearwaters
occur in the entire Bering Sea in summer. Sanger and
Baird (1977b) estimated a total of 10 million. By
everyone's reckoning, the Short-tailed Shearwater is
the most abundant bird species in the Bering Sea
from June through September.
Shearwaters take a variety of euphausiids, squid,
and fish (Sanger and Baird 1977a). They capture
their quarry by surface seizing, shallow plunges, and
pursuit under water.
Shuntov (1972) summarized much of what is
known about the pelagic biology of these shearwaters
in the Pacific. His findings of an entry into the Be-
ring Sea through the Aleutian passes in May and June
and a departure starting in September and peaking in
October are in agreement with our observations.
Pe lagic d is I rib ution 697
Shuntov added the interesting observation that the
distribution of shearwaters shifts from the continen-
tal shelf areas in the first half of the summer to the
deeper waters between the Pribilof Islands and
Unimak Pass in the second half. Bartonek and
Gibson (1972) found large numbers of shearwaters
throughout the areas of Bristol Bay surveyed in July,
but noticed a considerable reduction of these num-
bers in August. This was about one month later than
reported by Shuntov (1961), who estimated that five
to seven million Short -tailed Shearwaters gathered to
molt in the southeastern Bering Sea in June of 1960,
but that by July, molt was essentially completed and
the birds were leaving that area.
On the average, shipboard surveys produced higher
density estimates of shearwaters than surveys from
fixed-wing aircraft. Both survey types appeared to
produce inflated density estimates because of the dif-
ficulty observers have in obtaining instantaneous
counts of birds vdthin a transect when birds are in
large, often rapidly moving flocks. At the level of an-
alysis used for this chapter, however, the two meth-
ods produced remarkably similar distribution and
density patterns. We have thus chosen to combine
shipboard and aerial surveys in order to display the
broadest level of perspective available.
We have no winter records of shearwaters in the
Bering Sea. Our earliest records are of one bird on
24 April and eight birds on 27 April. Our latest rec-
ords are of one bird on 21 November and two birds
on 22 November. All four records were from waters
immediately north of the Aleutian Islands. Spring,
summer, and fall distributions of shearwaters are
shown in Figs. 40-15 to 40-17. The majority of
these birds move into the Bering Sea in May and June
and leave in September and October. A fair number
move into Arctic seas with high densities reported
from the area of the Bering Strait (see Swartz 1967).
The most striking features of shearwater distribu-
tion are its patchiness and the possibility of encoun-
tering foraging or resting flocks of immense size.
Flocks of more than 100,000 birds were not uncom-
mon, and aggregations of over 1,000,000 have been
recorded.
These two species usually occurred over the conti-
nental shelf, and moderate numbers sometimes oc-
curred over the shelf break, especially in the fall. A
few birds were found over waters deeper than
2,000 m. In the Bering Sea, they were concentrated
near and inside the 50-m isobath. This area of shallow
water is a zone in which the water column is mixed
from the surface to the bottom and therefore may be
Figure 40-15. Pelagic distribution of shearwaters— air and
siiip surveys: Marcii-May.
Figure 40-16. Pelagic distribution of shearwaters— air and
ship surveys: June-August.
698 Marine birds
Figure 40-17. Pelagic distribution of shearwaters— air and
ship surveys: September-November.
especially productive. Our observations neither con-
firm nor refute the shifts of birds into and out of
Bristol Bay reported by Shuntov (1972) and
Bartonek and Gibson (1972).
Contrary to Shuntov's (1972) opinion that his esti-
mates of tube-nosed birds were high, our data suggest
that his and other estimates were low. Our absolute
minimum estimate is that 9 million shearwaters occur
in the eastern Bering Sea in summer, and that average
numbers are probably more on the order of 20 mil-
lion, with more than 45-65 million possibly occurring
during peak periods.
Our records indicate that Sooty Shearwaters make
up less than 10 percent of the total shearwaters in the
eastern Bering Sea, and that they are generally con-
fined to the most southern part of that area. We also
suspect that the number of Sooty Shearwaters in the
Bering Sea is highly variable between years and that
the proportion of this species may vary between sea-
sons. Whichever value is used and whatever the spe-
cies composition, the impact of shearwaters on Bering
Sea ecosystems must be high.
Gadfly Petrels (Pterodroma spp.)
The Mottled Petrel (P. inexpectata) is a regular non-
breeding visitor (July-October) to the Bering Sea,
where it is found in low numbers and apparently re-
stricted to oceanic waters south of 56° N. Cook's
Petrel (P. cookii) may visit waters of the western Be-
ring Sea, but the only record to date is a specimen
taken near Adak, Alaska.
Fork-tailed and Leach's Storm-Petrels (Oceanodroma
furcata and O. leucorhoa)
In the Bering Sea, Fork-tailed and Leach's Storm-
Petrels breed only on the Komandorsky and Aleutian
islands; there are relatively few known breeding sites
for the Leach's Storm-Petrel. The general similarity
in breeding distribution, however, is not reflected in
their pelagic distributions. As suggested by Murie
(1959) and supported by Bartonek and Gibson
(1972), Shuntov (1972), and Wahl (1978), Leach's
Storm-Petrels range mostly south of the Aleutian
Islands into the deep waters of the northwestern Paci-
fic, while Fork-tailed Storm-Petrels are abundant in
the Bering Sea. Swartz (1967) reported no sightings
of storm-petrels in the Bering Strait region or Chuk-
chi Sea. Shuntov's data indicated that Fork-tails
reach their highest densities over shelf and depression
areas and that their numbers exceeded four million in
the Bering Sea. Shuntov and Wahl agreed that, be-
cause of reduced numbers of other species. Fork-tails
form the largest percentage of seabirds over deep-
water areas. So wis et al. (1978) estimated popula-
tions of 2.3 million Fork-tails and 1.9 million Leach's
in the Aleutian Islands area.
Storm-petrels obtain their food either by surface
seizing or pattering. Although we have virtually no
data on their diet in the Bering Sea, Fork-tails are
known to take small fish, cephalopods, and fish offal
(Ainley and Sanger 1979). Both species nest coloni-
ally on offshore islands and are strictly nocturnal in
flights to and from their burrows. Both species have
long incubation shifts which allow them to forage at
great distances from their nests (Boersma and
Wheelwright 1979).
Shipboard surveys tended to produce higher den-
sity estimates of storm-petrels than aerial surveys, al-
though the results were inconsistent when analyzed
on a survey-by-survey basis. Fork-tails are attracted
to ships, but this bias may, to some degree, be com-
pensated for by the difficulty of detecting such small
birds at distances greater than 200 m. Aerial surveys
are almost certain to underestimate storm-petrel num-
bers because of the difficulty of spotting such small,
cryptically colored birds. The two survey methods
produced remarkably similar distribution patterns
and we have thus chosen to combine shipboard and
aerial surveys for our analysis. We present only data
for total numbers of storm-petrels encountered. Al-
though occasional Leach's Storm-Petrels were re-
corded, numbers of this species were insignificant and
Pelagic distribution 699
our maps thus primarily reflect data from Fork-tailed
Storm-Petrels.
The pelagic distribution of storm-petrels is given in
Figs. 40-18 to 40-20. Spring, summer, and fall sur-
veys showed storm-petrels, mostly Fork-tails, concen-
trated in the southeastern Bering Sea, with moderate
numbers inshore to the 100-m isobath. Very few
storm-petrels were seen north of 58° (our northern-
most record is of four Fork-tailed Storm-Petrels in
September in the Bering Strait) or inshore of the 100-
m isobath, except in fall, when there were scattered
records of birds over the shallow waters of northern
Bristol Bay. Fork-tailed Storm-Petrels were seen over
deep ocean water, but not over shelf waters during a
single winter aerial survey. Most of our records of
Leach's Storm-Petrels were from the deep water im-
mediately north of the central Aleutian Islands. We
have only three records of this species over the conti-
nental shelf of the eastern Bering Sea (two in May
and one in July), and these were all in Bristol Bay.
The scarcity of Fork-tailed Storm-Petrels in the
northern Bering Sea may be a function of the loca-
tion of nesting colonies. Even though they are
known to forage at great distances from their nest
sites (Boersma and Wheelwright 1979), they may not
forage as far as these waters. It is unlikely that the
Figure 40-18. Pelagic distribution of storm-petrels— air and
ship surveys: March-May.
160°
155°
Figure 40-19. Pelagic distribution of storm-petrels— air and
ship surveys: June-August.
Figure 40-20. Pelagic distribution of storm-petrels— air and
ship surveys: September-November.
700 Marine birds
lack of appropriate foods would exclude them from
this region, particularly the deeper waters of the Gulf
of Anadyr.
Our finding of few storm-petrels over the shallow
waters of Bristol Bay is in agreement with the results
of Bartonek and Gibson (1972). They found, how-
ever, as we did to a lesser extent, small numbers
over water somewhat shallower than 100 m at about
56°N, 163-164°W. A paucity of appropriate foods
may be the cause of low numbers inside the 100-m
isobath. Just inside the middle front, there is a
marked decrease in the abundance of oceanic forms
of plankton, in particular of the large species of Cala-
nus (Cooney, this volume). If these or other food
species sensitive to oceanographic changes occurring
at the middle front are the principal foods exploited
by storm-petrels, then the scarcity of Fork-tails
inshore of the 100-m isobath is understandable.
Estimates from combined shipboard and aerial sur-
veys indicate the presence of about four million
storm-petrels over eastern Bering Sea waters. Highest
densities occur over deep waters.
Cormorants (Phalacrocorax spp.)
Three species of cormorants nest in the Bering Sea:
the Double-crested Cormorant (P. auritus), the
Pelagic Cormorant (P. pelagicus), and the Red-faced
Cormorant (P. urile). The nesting distributions of
these species in the Bering Sea are treated in Sowls et
al. (1978) and Hunt et al. (Chapter 39, this volume).
Cormorants get their food by pursuit diving and
frequently forage near the bottom. They eat a wide
variety of fish, shrimp, and crabs (Hunt et al..
Chapter 38, this volume).
During the summer months cormorants were usu-
ally found within a few kilometers of their colonies
and there were few sightings of birds in the open
ocean. In spring and more particularly in fall, small
numbers were found far at sea. Aleuts on the Pribilof
Islands have told us that of all marine bird species,
cormorants are the most likely to remain on the cUffs
throughout the winter if open water is available. Birds
seen on the open sea away from island rookeries may
have been post-breeding wanderers or migrants dis-
placed from northern areas by encroaching ice.
Phalaropes (Phalaropus spp.)
Both Red (P. fulicarius) and Northern Phalaropes
(P. lobatus) are abundant in the eastern Bering Sea.
Their breeding distribution and movements in this
area are described by Gill and Handel (Chapter 41,
this volume). Breeding birds are generally restricted
to wetland habitats but nonbreeders and migrants re-
ly heavily on marine waters. Phalaropes feed on small
aquatic organisms which they obtain by dipping from
the surface.
We have records of phalaropes from 25 May
through 14 October; more than 60 percent of the
sightings occurred in September and October. Most
of these were over waters shallower than 200 m ex-
cept in the western Aleutians and the airea just north
and east of Unimak Pass, where many occurred over
the shelf break. BroviTi (1980) has summarized the
importance of convergence fronts and eddies to phal-
aropes as a means of concentrating their planktonic
foods.
Phalaropes are small and difficult to detect except
in large flocks. Densities obtained from shipboard
and aerial surveys must therefore be considered un-
derestimates. Combined ship and air surveys indi-
cated a minimum pelagic population of about one
million phalaropes in summer and fall in the eastern
Bering Sea.
Jaegers (Stercorarius spp.)
Pomarine Jaegers (S. pomarinus). Parasitic Jaegers
(S. parasiticus), and Long-tailed Jaegers (S. longicau-
dus) nest in the eastern Bering Sea region. Parasitic
Jaegers have the widest north-south breeding range.
After breeding, all three species disperse to sea. The
entire population moves out of the Bering Sea in win-
ter and does not return until May. Walleye pollock
(Theragra chalcogramma) and capelin (Mallotus villo-
sus) have been recorded from stomachs of birds col-
lected over pelagic waters in Alaska. Jaegers are
found in low numbers throughout all marine habitats
in the eastern Bering Sea and we can detect no corre-
lations between their distributions and any environ-
mental feature. All three species are well known as
kleptopEirasites and their distributions in the eastern
Bering Sea may reflect this behavior, with jaegers oc-
curring throughout the ranges of their host species.
Gulls (Rhodostethia, Pagophila, Xema, and Larus
spp.)
Including kittiwakes, at least 14 species of gulls
have been recorded in the eastern Bering Sea. Of
these, five are rare or accidental: Slaty-backed Gull
(L. schistisagus), Thayers Gull (L. thayeri). Western
Gull (L. occidentalis). Black-headed Gull (L. ridibun-
dus), and Ross's Gull (R. rosea).
Bonaparte's Gull (L. Philadelphia) breeds from Ko-
buk Bay to the head of Bristol Bay but rarely occurs
over marine waters away from its few coastal breed-
ing sites.
Small numbers of Mew Gulls (L. canus) breed in
coastal areas of the eastern Bering Sea, but most indi-
Pe lafiic d « / rib ution 701
viduals remain in protected waters near their colonies
and few have been recorded on our surveys.
Herring Gulls are represented by the race L. argen-
tatus vegae, which breeds in small numbers on St.
Lawrence Island. Their pelagic distribution is almost
completely unknovm.
Sabine's Gulls (X. sabini) breed along the Arctic
and Bering sea coasts south to northern Bristol Bay.
Little is known about their pelagic distribution and
behavior except that they make extensive pelagic mi-
grations to the southern hemisphere in winter where
they use eastern boundary upwellings off Ecuador
and Peru (Murphy 1936) and southwest Africa
(Lambert 1971). Our records showed small numbers
of birds scattered throughout the entire eastern Be-
ring Sea, with most sightings in September.
The Ivory Gull (P. eburnea) visits the Bering Sea
only in winter, when small numbers are found
along the leading edge of the pack ice, occasionally as
far south as the western edge of Bristol Bay. This is
one of the few species of marine birds in the northern
hemisphere that are highly adapted to life with pack
ice, and it is seldom found in areas of extensive open
water.
The most abundant species of large gulls in the
eastern Bering Sea are the Glaucous Gull (L. hyperbo-
reus) and Glaucous-winged Gull (L. glaucescens).
Basically, Glaucous Gulls breed in the northern half
of the area while Glaucous-winged Gulls breed in the
southern half, with overlap in the Cape Newenham/
Nunivak Island area. Glaucous-winged Gulls are the
more abundant of the two species: their Aleutian
Island /eastern Bering Sea population has been esti-
mated at 130,000, compared to 30,000 for Glaucous
Gulls (Sowls et al. 1978). Both species eat a wide
variety of food, from carrion and offal to assorted
marine organisms and small fish. Both occur regular-
ly throughout the year in ice-free waters of the east-
em Bering Sea with large numbers in nearshore areas
decreasing outward to scattered individuals over
oceanic waters.
Black-legged Kittiwake (Rissa tridactyla)
The Black-legged Kittiwake is perhaps the best
known of all the seabird species that breed in the
eastern Bering Sea. Large colonies occur on precipi-
tous and predator-free cliffs of all major islands and
coasts throughout the area. Sowls et al. (1978) esti-
mated that a total of about 1.1 million Black-legged
Kittiwakes are associated with colonies in the eastern
Bering Sea/ Aleutian Islands area, and Shuntov (1972)
indicated an at-sea population of about 1.5 million
for the entire Bering Sea. This is one of the most
pelagic of gulls.
Black-legged Kittiwakes forage on a wide variety of
small fish and large zooplankters which they take
from within 0.25 m of the ocean's surface (Hunt et
al., Chapter 38, this volume). These birds apparently
forage primarily as scattered individuals. When an
abundant source of food is discovered, birds from the
surrounding area converge. After the food ceases to
be available, the birds disperse to begin solitary for-
aging again. Kittiwakes apparently are the major
catalysts in the formation of mixed-species feeding
flocks in Alaskan waters (Wiens et al. 1978). Such
behavior may contribute substantially to the foraging
success of other pelagic bird species.
Shuntov (1972) provided a discussion of the pel-
agic biology of Black-legged Kittiwakes in the Bering
Sea. He recorded them in all ice-free waters through-
out the year, and suggested an orientation towards
land in the summer months. At this time they are es-
pecially attracted to the mouths of rivers. In the Ko-
diak area of the Gulf of Alaska, Gould et al. (1978)
found this species to become particularly abundant
in bays from July to September with a concur-
rent but small reduction in numbers over the conti-
nental shelf. Shuntov provided the additional infor-
mation that Black-legged Kittiwakes disperse in Sep-
tember and October, not only over the shelf, but also
over the oceanic waters. Shortly thereafter the major
portion of the population leaves the Bering Sea for
nomadic wandering in the Pacific. According to
Shuntov, these kittiwakes return to the Bering Sea in
early April. Swartz (1967) believed that most breed-
ing Black-legged Kittiwakes foraged fairly close to
their colonies in the Bering Strait and Chukchi Sea,
and that individuals found far from land were non-
breeding birds.
A comparison of shipboard and aerial data showed
striking similarity between the results of the two
types of survey. Aerial surveys tended to have more
zero densities reported, but they also reported more
areas of moderate concentrations. Shipboard data ap-
peared remarkably free of bias due to ship-following.
We have thus chosen to use the combined shipboard
and aerial data for this presentation. We also include
unidentified kittiwakes under Black-legged Kittiwake.
Virtually all kittiwakes away from the Pribilofs are
Black-legged, and most surveys done near the Prib-
ilofs were conducted by people able to distinguish the
two species. By including unidentified kittiwakes
with Black-legged Kittiwakes we greatly increase our
knowledge of areas covered primarily by aerial sur-
veys in which kittiwakes were not identified to spe-
cies.
The pelagic distribution of Black-legged Kittiwakes
in spring, summer, and fall is given in Figs. 40-21 to
102 Marine birds
40-23. In these seasons, birds were found throughout
the shelf waters surveyed in low and surprisingly
evenly distributed numbers. Although occasional
concentrations were found in the vicinity of fishing
vessels, there were no obvious gradients in Black-
legged Kittiwake density in summer as major breeding
colonies were approached. Densities may have been
lower over the deep oceanic waters, but sampling in
this region was insufficient. In spring and fall, aerial
surveys revealed larger concentrations near the north
side of the Aleutian chain and in the vicinity of Uni-
mak Pass than were found on shipboard surveys. Aer-
ial surveys in winter failed to find birds in Bristol
Bay, although very low numbers were seen over deep
oceanic water southeast of the Pribilof Islands. These
findings generally agree vdth those of Shuntov (1972).
Our data show no evidence that Black-legged Kitti-
wakes concentrate their foraging with respect to any
obvious oceanographic feature.
Combined density estimates for the eastern Bering
Sea/Aleutian area indicate a pelagic population of
two to three million birds in summer and fall. These
figures exceed those of Sowls et al. (1978) and
Shuntov (1972).
Figure 40-21. Pelagic distribution of Black-legged Kitti-
wakes —air and ship surveys: March -May.
165°
175° 170° 165°
160°
160°
Figure 40-22. Pelagic distribution of Black-legged Kitti-
wakes —air and ship surveys: June-August.
Figure 40-23. Pelagic distribution of Black-legged Kitti-
wakes —air and ship surveys: September-November.
Pelagic distrihulion 703
Red-legged Kittiwake (Rissa breuirostris)
Red-legged Kittiwakes are endemic to the Bering
Sea, and the major portion of the population nests on
the high cliffs of St. George Island. Smaller popula-
tions nest on Bogoslof and Buldir islands, and pos-
sibly in the Komandorskys. Sowls et al. (1978) esti-
mated a total Red-legged Kittiwake population of
about 250,000. This species is, if anything, even
more pelagically oriented than the Black-legged Kitti-
wake.
Red-legged Kittiwakes forage on a variety of small
fish and large zooplankters which they take from
within 0.25 m of the ocean's surface (Hunt et al..
Chapter 38, this volume). In particular, a large por-
tion of their diet consists of myctophid fishes (Hunt
et al. 1980), a deepwater group rarely, if ever, found
in shelf waters.
Shuntov (1963) depicted the summer distribution
of Red-legged Kittiwakes as occurring throughout the
deeper waters of the Bering Sea with no birds over
the shallower waters in the north and east. Highest
densities were in and near the shelfbreak area and to
the north, east, and south of the Pribilof Islands.
Shuntov gave densities of up to three to six birds
per km' in this area. He suggested that a major por-
tion of the population moves south out of the Bering
Sea in the winter. In June-July of 1975, Wahl (1978)
found Red-legged Kittiwakes to outnumber Black-
legged Kittiwakes over waters deeper than 2,000 m
to the northwest and southwest of the Pribilofs. He
found no birds between Hokkaido and the Aleutian
Islands and none east of about 177°W in the south-
east Bering Sea. Bartonek and Gibson (1972) re-
corded three birds in Bristol Bay in August.
For this species we have relied solely on shipboard
censuses. Problems with identification from the air
caused observers to record most kittiwakes seen as
unidentified, thus resulting in an underestimate of
Red-legged Kittiwakes in areas they are known to
frequent (see Black-legged Kittiwakes). Shipboard
densities may be exaggerated, since this species
will join ships in order to forage on offal.
The pelagic distribution of Red-legged Kittiwakes
in spring, summer, and fall is given in Figs. 40-24 to
40-26. In these seasons, most of these birds were
found between the Pribilof Islands and the shelf
break. While some birds foraged to the west of the
islands, particularly in spring and fall, most were
found to the south of St. George Island. Only low
densities of this species were found over water shal-
lower than 100 m, and very few individuals were
seen north of 59°N or east of 165°W. Little is known
of their winter distribution, but at least some Red-
legged Kittiwakes apparently disperse into the Gulf
17 5°
165°
Figure 40-24. Pelagic distribution of Red-legged Kitti-
wakes—ship surveys: March-May.
160°
Figure 40-25. Pelagic distribution of Red-legged Kitti-
wakes—ship surveys: June-August.
704 Marine birds
170° 165
Figure 40-26. Pelagic distribution of Red-legged Kitti-
wakes— ship surveys: September-November.
of Alaska in this season. A few have been recorded
in vdnter over oceanic waters in the southern Bering
Sea.
The asymmetry of the distribution of Red-legged
Kittiwakes around the Pribilof Islands is striking.
Their numbers are clearly more concentrated near
the shelfbreak, where myctophids are found, and
they are most common where the shelf break is
closest to their nesting habitat. The preference for
myctophids in their diet, and the restriction of these
fish to deep water, may explain why Red-legged
Kittiwake colonies are found only on islands close to
the shelfbreak and why much of their foraging is noc-
turnal. In the evenings they were seen streaming
south from St. George Island, and large numbers were
recorded returning to the island in the morning.
Terns (Sterna spp.)
Arctic Terns (S. paradisaea) and Aleutian Terns (S.
aleutica) are regular breeding visitors to the eastern
Bering Sea and a few sightings of vagrant Common
Terns (S. hirundo) have been reported from the
Aleutian Islands. These terns forage mostly in bays
and nearshore areas where they obtain small fish,
euphausiids, and other small organisms from surface
waters by plunge diving and dipping from the air.
Only small numbers are recorded by ship and air sur-
veys over pelagic waters and most deep-water records
are from the post-breeding period of August-
September. Arctic and Aleutian Terns leave the
Bering Sea soon after the young are fledged, the
former migrating south, and the latter apparently
moving into the northwest Pacific.
Common and Thick-billed Murres (Uria aalge and U.
lomuia)
Murres are abundant and widespread in all marine
habitats of Alaska. Their numbers are especially high
in the Bering Sea, where large colonies occur on all
major islands and coastlines that have high, predator-
free cliffs. The largest breeding aggregation of murres
in Alaska (ca. 1.85 million) is located on the Pribilof
Islands. Sowls et al. (1978) estimated that there are
about 7.3 million murres (55 percent Thick-billed)
associated with breeding colonies in the eastern Be-
ring Sea/Aleutian Islands area. Tuck (1960) placed
the North Pacific population at about 20 million and
the world population at about 56 million. Shuntov
(1972) estimated a pelagic population in the Bering
Sea in summer of about 3.2 million Thick-billed
Murres, but it is not clear whether or not he included
Common Murres in this total.
Murres feed by diving, often to great depths. Both
species forage on small fish and, particularly the
Thick-billed Murre, on large zooplankters such as
Parathemisto (Hunt et al.. Chapter 38, this volume).
Shuntov (1972) summarized most of the available
data on the pelagic biology of murres in the Bering
Sea. He found murres abundant throughout the year,
and most common over the continental shelf. After
breeding, there is wadespread dispersal to sea but
most of the population apparently remains over the
shelf. In summer, Bartonek and Gibson (1972)
found large numbers throughout Bristol Bay, mostly
between the 50-m isobath and the shore. Wahl
(1978) found murres most abundant over shelf waters
near major colonies.
In the Chukchi Sea, Swartz (1967) found murres
decreased in abundance as he crossed from waters
colder than 10 C to warmer waters near Kotzebue
Sound. Deeper into Kotzebue Sound, the fact that
numbers of murres did not increase when a drop in
water temperature was encountered emphasizes the
difficulty in drawing simple correlations of bird num-
bers with any one environmental parameter. Swartz
also found that murres usually foraged within about
64 km, and most within 48 km, of their colonies. His
observations on the percentage of the two species of
murres on the cliffs and at sea suggest that Common
Murres forage closer to their colonies (possibly
mostly within 8 km) while Thick-bills forage further
Pelagic clislrihution 705
offshore. This notion is consistent with Swartz's
(1966) findings on food habits.
Since Common and Thick-billed Murres are diffi-
cult to tell apart in the field, particularly from air-
craft, the data for the two species have been com-
bined in this chapter. Likewise, aerial and shipboard
surveys are combined to provide the most compre-
hensive distributional patterns. Both survey types
tend to underestimate murre densities, and aircraft
surveys seem especially prone to miss single birds
and small flocks.
Murres showed considerable seasonal variation in
distribution (Figs. 40-27 to 40-30). In springtime
they were found throughout the continental shelf
waters, with moderate densities along the 100-m to
200-m curves from Unimak Pass to the Pribilof Is-
lands. Highest densities were found near the 50-m
isobath (inner front) just north of the Alaska Pen-
insula at about 163-1 64° W. Even though it was a
considerable time before the beginning of egg-laying,
elevated numbers were found near the Pribilof Is-
lands and the Walrus Islands. The northern extent of
the pelagic distribution at this season was determined
by the pack ice.
In summer, most murres were found in the vicinity
of the major colonies, near the Pribilofs, Cape Newen-
ham, Nunivak Island, St. Matthew Island, and St.
Lawrence Island. Elsewhere, moderate densities were
Figure 40-27. Pelagic distribution of murres— air and ship
surveys: March-May.
17 5° 170° 165"
170'
165°
Figure 40-28. Pelagic distribution of murres— air and ship
surveys: June-August.
Figure 40-29. Pelagic distribution of murres— air and ship
surveys: September-November.
706 Marine birds
175° 170° 165°
Figure 40-30. Pelagic distribution of murres— air surveys:
December-February.
found throughout continental shelf waters and very
low densities were recorded over oceanic waters.
Only very few sightings of birds with young were
made, and these were scattered in areas frequented by
foraging adults without chicks. We did not find any
major staging areas where flightless adults with chicks
congregated, as apparently occurs in other parts of
the world. Such staging areas should be looked for
with care in Alaska.
In the fall, moderate numbers of murres were scat-
tered over the continental shelf, especially between
the 50-m and 100-m isobaths. Only one concentra-
tion was detected, an extremely large number of
birds about 275 km due north of St. Paul Island.
Murres were the most abundant seabird species
wintering in the Bering Sea, especially over open
waters of the continental shelf.
Our preliminary density estimates indicate a total
pelagic population of 2.5 million birds in the fall and
5.0 million in the summer. These estimates are con-
siderably below those calculated from Sowls et al.
(1978). The discrepancy results from the fact that
murres at most of the large Bering Sea colonies ap-
pear to forage close to their colonies and these con-
centrations result in a drastic underestimation of pop-
ulation size based on pelagic densities. In other parts
of their range, murres may feed at considerable dis-
tances from their colonies (Nettleship and Gaston
1978).
Parakeet, Crested, and Least Auklets (Cyclorrhynchus
psittacula, Aethia cristatella, and A. pusilla)
Parakeet, Crested, and Least Auklets are the major
species of small alcids that nest on the islands of the
eastern Bering Sea. The breeding of the Least and
Crested Auklets in the Bering Sea is primarily re-
stricted to the Aleutian Islands, the Pribilofs, the west
end of St. Lawrence Island, King Island, and the Dio-
medes. At all these colonies, Least Auklets are more
abundant than Crested Auklets. The Parakeet Auklet
also nests on these islands, but unlike the other two
species, it nests in small numbers on more coastal is-
lands and headlands as well.
Sowls et al. (1978) estimated that 0.6 million Para-
keet Auklets, 1.9 million Crested Auklets, and 6.0
million Least Auklets are associated with breeding
colonies in the eastern Bering Sea/Aleutian Islands
area. Shuntov (1972) estimated a pelagic population
in the Bering Sea in summer of about 2.1 million
smaU alcids.
The food habits and foraging behavior of these
small auklets are perhaps better known than those of
any other alcids. Bedard (1969), in detailed studies
on St. Lawrence Island, characterized not only the
types of foods preferred, but also the size-classes
taken and the distance from the colony at which for-
aging takes place. Least Auklets take the smallest
items and Bedard (1969) and Hunt et al. (1978)
found them to specialize on large copepods, particu-
larly of the genus Calanus, for feeding their young.
Other foods include carid shrimp, euphausiids, and
amphipods. Crested Auklets take somewhat larger
items, although there is considerable overlap with
Least Auklets (B6dard 1969). Crested Auklets use
primarily euphausiids, but also take copepods and oc-
casionally amphipods (B6dard 1969, Hunt et al.
1978). Parakeet Auklets also make extensive use of
euphausiids, but amphipods and to a lesser extent
larval fish are important parts of their diet (B6dard
1969, Hunt et al. 1978). Food use by these auklets
is reviewed by Hunt et al. (Chapter 38, this volume).
Shuntov (1972) suggested that, although they oc-
cur in all ice-free waters of the Bering Sea throughout
the year, many small alcids disperse to the south
where they either concentrate near the Aleutian
and Komandorsky islands or pass through the Aleu-
tian chain to waters of the North Pacific. Although
Bartonek and Gibson (1972) found moderate num-
bers of murrelets in the southeastern Bering Sea in
July and August, they found no Parakeet Auklets or
Least Auklets and only one Crested Auklet. Weath-
er conditions prevented Wahl (1978) from obtain-
ing good counts of small auklets, but he did record
large concentrations near Amchitka Pass.
Pelagic (list rib u lion 70 7
For the purposes of this presentation, the data on
the pelagic distribution and abundance of these three
auklets have been combined. Parakeet Auklets, while
they have a more widespread distribution, are too
scarce to cause significant shifts in the distribution
maps. Both shipboard and aerial surveys tend to
underestimate the densities of small alcids, and aerial
surveys are especially prone to missing single birds
and small groups. Aerial surveys are combined here
with shipboard surveys to give the most complete
coverage.
The pelagic distribution of small auklets in the
Bering Sea is given in Figs. 40-31 to 40-33. Uniden-
tified small auklets are not included in these figures.
In spring, auklets were numerous in the southeastern
Bering Sea, particularly over shelf waters. For the
most part they were present only in low densities, but
several areas with large concentrations were encoun-
tered. It is possible that some of these concentra-
tions reflect ice-edge phenomena, as discussed by
Divoky (Volume 2). In the spring all three species
of auklets will form dense rafts in leads in the ice
(Bedard 1967), similar to those formed by Dovekies
(Alle alle) near pack ice (Brown in press).
Summer distributions reflect primarily the distri-
bution of major breeding colonies in the Pribilofs,
the west end of St. Lawrence Island, and the Bering
Figure 40-31. Pelagic distribution of small auklets— air and
ship surveys: March-May.
17 5° 17 0°
175°
160°
175° 170° 165°
175°
165°
Figure 40-32. Pelagic distribution of small auklets— air and
ship surveys: June-August.
Figure 40-33. Pelagic distribution of small auklets— air and
ship surveys: September-November.
708 Marine birds
Strait. At this season virtually no auklets were found
in either Bristol Bay or Norton Sound, and except
for a few scattered birds along the middle front, few
auklets were seen far from colonies. Auklets often
forage close to their colonies, sometimes in large
flocks. Least Auklets at St. Lawrence Island may for-
age near the shore, or out to 30-50 km offshore (Be-
dard 1967, 1969), but at the Pribilofs, they were al-
most always within 5-10 km of shore (Hunt et al.
1978). Likewise, Crested Auklets were usually
found foraging within a kilometer or so of shore
(Bedard 1967, 1969; Hunt et al. 1978). Both of
these species form large flocks, particularly after feed-
ing (Bedard 1969). Parakeet Auklets also forage close
to their colonies, but occasionally they were found
several tens of kilometers offshore, usually as single
birds or in small flocks (Bedard 1969, Hunt et al.
1978).
In fall, auklets were still found in large numbers in
the western waters of the Bering Strait and west of
St. Lawrence Island, where the deeper waters origi-
nating in the Aleutian Basin would support the larger
calanoids upon which the Least and Crested Auklets
forage (T. Kinder, NORDA, personal communica-
tion). In the southeastern Bering Sea, the concentra-
tions around the Pribilof Islands disappeared, to be
replaced by low densities of birds spread fairly evenly
from the shelf break eastward into Bristol Bay. This
intrusion into Bristol Bay was not entirely expected,
since the large calanoids are generally not found in
largo numbers shoreward of the middle front (100-m
isobath). Perhaps birds in Bristol Bay were foraging
on small euphausiids, which may be plentiful there
(Cooney, this volume).
Estimates of these three auklets based on com-
bined shipboard and aerial surveys indicate minimum
populations in the eastern Bering Sea ranging from
1.0 to 3.0 X 10^ in summer and fall. These figures
are much lower than estimates derived from Sowls et
al. (1978). The discrepancy results from the fact that
these small auklets are hard to detect, and at least
around the Pribilof Islands, since they concentrate
their foraging near this colony, they were over-
looked by pelagic surveys that spent little time very
close to land. Furthermore, most auklets breed in
the northern islands (Sowls et al. 1978; Hunt et al..
Chapter 39, this volume), an area that has received
relatively little survey coverage.
Horned Puffins (Fratercula corniculata)
Homed Puffins nest throughout the Bering Sea in
rock crevices. They tend to be somewhat more abun-
dant nesters in the northern Bering Sea than in the
south, but nowhere in the Bering Sea are they a dom-
inant species. Sowls et al. (1978) estimated that
about 0.35 X 10^ Horned Puffins are associated with
breeding colonies in the eastern Bering Sea/Aleutian
Island area.
Horned Puffins forage on small fish, cephalopods,
and large zooplankters by pursuit diving (Hunt et al..
Chapter 38, this volume). In general, most OCSEAP
observers have concluded that Homed Puffins restrict
their foraging efforts during the breeding season to
vidthin a few kilometers of their colonies. Thus, rela-
tively few individuals of this species were seen during
wide-ranging pelagic surveys.
Homed Puffins are relatively uncommon in the
Bering Sea, and there is little information published
on their pelagic biology. Bartonek and Gibson
(1972) found small numbers offshore in Bristol Bay
and relatively large numbers only in Unalaska Bay.
Wahl (1978) sighted only a few near the Pribilofs and
in Bristol Bay just north of the Alaska Peninsula.
Shuntov (1972) made no mention of this species.
The winter distribution of this species is reviewed by
Wiensetal. (1978).
Because aerial and shipboard surveys provided
comparable information, we have combined the aerial
and shipboard survey data in order to provide maxi-
mum coverage.
The distribution of Horned Puffins in spring, sum-
mer, and fall is given in Figs. 40-34 to 40-36. In
March through May, virtually no Homed Puffins were
recorded in the Bering Sea. The few seen were south
and east of St. George Island. By summer, small
numbers were present in the vicinity of breeding colo-
nies throughout the Bering Sea. Low densities were
also encountered east and northeast of the Pribilofs.
In the fall (Fig. 40-36), some Horned Puffins were
still present in the Bering Strait, but most were
found in the southeastern Bering Sea. Homed Puffins
were generally absent from Norton Sound and inner
Bristol Bay in all seasons, and from the entire Bering
Sea in winter.
Tufted Puffin (Lunda cirrhata)
Tufted Puffins nest throughout the Bering Sea, but
their colonies are larger and more numerous in the
southern part. Where foxes are a threat, burrows are
restricted to fox-free sections of cliff face with suffi-
cient soil; where foxes are absent, Tufted Puffins nest
on the tops of islands and on gentle slopes. Sowls et
al. (1978) estimated that about 1.7 milhon Tufted
Puffins are associated with breeding colonies in the
eastern Bering Sea /Aleutian Islands area.
Tufted Puffins forage for fish by pursuit diving.
They also take nereid worms, cephalopods, and large
zooplankters (Hunt et al.. Chapter 38, this volume).
Pe logic distribution 709
175° 170° 165°
175°
175° 170'
165° 160°
r.r;
Figure 40-34. Pelagic distribution of Horned Puffins— air
and siiip surveys: March-May.
Figure 40-35. Pelagic distribution of Horned Puffins— air
and ship surveys: June-August.
175°
170°
165°
Figure 40-36. Pelagic distribution of Horned Puffins— air
and ship surveys: September-November.
In general, Tufted Puffins are individual foragers, al-
though some rafting does occur, particularly in sum-
mer and fall (Wehle 1979, Nysewander 1975). In
w^inter, the birds become highly solitary.
Figs. 40-37 to 40-39 show the pelagic distribution
of Tufted Puffins in the Bering Sea. In spring, sum-
mer, and fall, they were widespread, occurring in
low densities in virtually all areas except innermost
Bristol Bay and Norton Sound. In spring, most Tuft-
ed Puffins were found over the shelfbreak and sea-
ward of the middle front, although there are records
of scattered occurrences in shallower waters. Densi-
ties were low, and occurrence spotty. In summer.
Tufted Puffins were spread uniformly at a low densi-
ty throughout the southeastern Bering Sea, with
smaller numbers in scattered locations north to the
Bering Strait and beyond. In the northern Bering Sea,
Tufted Puffins appeared to be more common near
island colonies, and were less frequently seen far from
colonies, as they were in the southern Bering. In fall,
the distribution appeared similar to that of summer,
except that several large concentrations were found.
In winter. Tufted Puffins leave the Bering Sea: none
were sighted on the one winter OCSEAP aerial survey.
Density estimates from our combined ship and aer-
ial surveys indicate a population of about 1.5 million
Tufted Puffins in the eastern Bering Sea in summer
and fall.
710 Marine birds
175°
170'
Figure 40-37. Pelagic distribution of Tufted Puffins— air
and ship surveys: Marcii-May.
Figure 40-38. Pelagic distribution of Tufted Puffins— air
and ship surveys: June-August.
175 170
Figure 40-39. Pelagic distribution of Tufted Puffins— air
and ship surveys: September-November.
Miscellaneous alcids (A lie, Cepphus, Brachyramphus,
Synthliboramphus, Ptychoramphus, Aethia, and
Cerorhinca)
Sixteen species of alcids, of which seven have al-
ready been discussed in this paper, have been record-
ed in the eastern Bering Sea. Distribution patterns
of the remaining nine species are highly varied. All
alcids feed primarily by pursuit diving, and euphau-
siids, shrimp, and other crustaceans are the favored
prey. The larger species include small fish in their
diets.
The Dovekie (Alle alle) and Black Guillemot (Cep-
phus grylle), rare in the Bering Sea, are generally
found only from St. Lawrence Island northward (Kes-
sel and Gibson 1978). Pigeon Guillemots (Cepphus
columba) and Kittlitz's Murrelets (Brachyramphus
breuirostris) breed throughout the eastern Bering Sea.
The former is fairly abundant and the latter uncom-
mon. Both species tend to remain in bays and near-
shore areas.
Marbled Murrelets (Brachyramphus marmoratus).
Rhinoceros Auklets (Cerorhinca monocerata), Cas-
sin's Auklets (Ptychoramphus aleuticus). Whiskered
Auklets (Aethia pygmaea), and Ancient Murrelets
( Sy nthliboramphus antiquus) breed only on the Aleu-
tian Islands, and their pelagic distribution rarely ex-
tends north of 54-58°N.
Pelagic distribution 711
Marbled Murrelets and Rhinoceros Auklets are
either very uncommon or are restricted to the bay
and nearshore waters which our surveys did not
cover. Our few records of Cassin's Auklets were
mostly near the inner front of the southeastern Be-
ring Sea. Whiskered Auklets are endemic to the
Bering Sea, where their distribution is closely linked
to the Aleutian Islands west of 166°W and south of
54°N.
We have a fair number of Ancient Murrelet sight-
ings, and these indicate a pelagic distribution related
to the inner front in the southeastern Bering Sea, in-
cluding Bristol Bay. This species relies heavily on
small fish and crustaceans such as euphausiids.
DISCUSSION
Mean seasonal and habitat density indices for the
major species and species groups of marine birds in
the entire eastern Bering Sea are presented in Table
40-1. Indices for the spring through fall period range
between 41 and 60 birds per km^ over shelf and
shelfbreak waters, and between 11 and 16 birds per
km^ over oceanic waters. These values are three to
four times greater than those obtained by Shuntov
(1972) and Wahl (1978). The highest densities for
total pelagic birds occur in summer and fall, but this
is almost entirely due to increased numbers of shear-
waters, and to the fact that clumped distribution pat-
terns of shearwaters and fulmars tend to produce arti-
ficially high density estimates. For species other than
shearwaters, overall density indices had a tendency to
peak in spring. This spring peak, however, is a
reflection of the concentrating effect that ice cover
has rather than an indication of a larger total popula-
tion. Birds returning from southern wintering areas
are prevented from spreading northward by the ice
front. Murres are the most abundant marine birds in
TABLE 40-1
Density indices (birds/km^ ) for seasons and habitats in the eastern Bering Sea.
Data are derived from combined ship and air surveys. Habitats include continental shelf (CS),
shelf breaii (SB), and oceanic (OC) waters.
Winter^
Spring
S
iimmer
Fall
Species/
Species group
CS
SB
OC
CS
SB
OC
CS
SB
OC
CS
SB
OC
Fulmar
1
3
2
3
11
2
3
16
3
12
35*^
9
Shearwaters
0
0
0
3
3
+
81^
13
3
35
lOl''
2
Storm-petrels
0
3
1
1
2
2
2
7
2
1
6
3
Larus gulls
-l-c
1
+
1
2
1
1
1
+
1
2
+
Kittiwakes
-1-
+
1
1
2
1
2
2
1
3
5
1
Alcids
16
2
2
34
20
5
15
17
2
9
3
2
Murres
14
0
0
19
2
1
9
1
+
4
1
+
Tufted Puffins
0
0
0
1
1
1
1
2
1
2
1
+
Total birds
.
minus shearwaters
and fulmars
24
6
5
50
27
10
25
29
5
18
18
4
Total birds ,
25
9
7
56
41
12
109*^
58
11
65
157''
16
^Based on a single aerial survey and no shipboard surveys.
''These densities are highly biased from sightings of large flocks.
'^All densities have been rounded to nearest whole number. A "+" indicates fewer than 0.5 birds/km"
712 Marine birds
the eastern Bering Sea in winter and spring, while
shearwaters dominate the marine avifauna in summer
and fall.
If we derive population estimates for total birds
minus shearwaters and fulmars, we obtain respective
summer and fall populations of 13 and 18 million sea-
birds from aerial surveys, 27 and 19 million from
shipboard surveys, or 24 and 18 million from com-
bined surveys. We believe the 18-19 million figure for
the fall to be correct; the figure of 27 million for the
summer appears to be somewhat high. If we then add
our best estimates of shearwaters (9-20 million) and
fulmars (1-2 million) to the combined estimates for
each season, we have a total pelagic marine bird
population in the eastern Bering Sea of 34-46 million
birds in summer and 28-40 million birds in the fall.
We believe that these estimates are conservative, even
though Shuntov (1972) estimated only 23.8 miUion
birds for summer in the entire Bering Sea and esti-
mates extrapolated from Sowls et al. (1978) indicated
26 million birds for summer in the eastern Bering
Sea /Aleutian Islands areas.
The pelagic distribution of marine birds in the east-
em Bering Sea varies greatly from species to species
and season to season. The general pattern is one of
highly mobile units, frequently single birds, scattered
over the ocean, coalescing into small or large assem-
blages for short periods, and then dispersing. This
produces a permutating web of high and low densities
over the surface waters of the eastern Bering Sea.
Fairly consistent patterns of frequent or infrequent
high densities may develop in different regions or
local areas depending on food availability and the spe-
cies of marine bird. A few species such as the Mot-
tled Petrel occur only over oceanic waters, and
others, such as Leach's Storm-Petrel, are most abun-
dant there. Northern Fulmars, Fork-tailed Storm-
Petrels, and Red-legged Kittiwakes are concen-
trated in shelfbreak waters with densities decreasing
in shallower water, especially shoreward of the
middle front. This pattern reflects the effect of
fronts in limiting the distribution and availability of
major food items. Fulmar distribution may be
heavily influenced by the fishing fleet, whose process-
ing ships dump large quantities of offal into the
water. Sooty and Short-tailed Shearwaters concen-
trate at and inshore of the inner front, where com-
plete vertical mixing of the water may result in high
populations of prey. Murres are typically birds of the
continental shelf, with most individuals clumped
around colonies in the summer. They also appear
highly gregarious in winter and spring. In fall, birds
accompanied by young apparently become widely
dispersed rather than concentrating in staging areas.
Distributions of Horned Puffin, Parakeet Auklet,
Crested Auklet, and Least Auklet are closely tied to
food sources near breeding sites. Tufted Puffins may
prefer to forage over deep waters but their pattern of
distribution is surprisingly uniform throughout the
eastern Bering Sea. This uniformity may be the result
of the distance these birds would have to travel to get
to deep water from colonies other than the Pribilof
and Aleutian Islands. Analysis of this problem,
however, is hindered by our limited sampling of
oceanic habitat. Black-legged Kittiwakes appairently
spread rather evenly throughout the marine environ-
ment.
The effect on bird distribution of frontal systems
in the Bering Sea is apparently different from that
typical of strong convergence (or divergence) fronts
(Murphy 1936, Pingree et al. 1974, Brown 1980).
At these fronts, lateral movements of water combined
with vertical movements result in either a concentra-
tion of food at the surface along a convergence line,
or the upwelling of nutrients and food items to the
surface from greater depths at a divergence. The
fronts in the southeastern Bering Sea wdth which
changes in bird fauna are associated mark boundaries
between shelf domains in which there axe marked
differences in the structure of the water column, and
there are no strong lateral movements at the surface.
Thus, at the inner front one passes from a well-mixed
system to a sharply divided two4ayer system (see
Chapter 3, Volume 1). With the possible exception
of the shelf-break and inner fronts, there are no
narrowly demarcated sharp increases in bird density
in the immediate vicinity of these fronts. Rather,
particular bird species are primarily associated with
one or more physically well-defined shelf domains
and the fronts are boundaries of both bird distribu-
tion and water structure.
Joiris (1978), working in the North Sea, identified
a similar influence of oceanography on bird distribu-
tion. He recognized two water bodies, Atlantic and
North Sea water. Atlantic water is characterized in
summer by salinities greater than 35<^/oo and tem-
peratures lower than 12.5 C; North Sea water in sum-
mer is less saline and warmer. Alcids were 12 times
denser in Atlantic water than in North Sea water and
Fulmars twice as dense; most small gulls were found
over North Sea waters. In distributions of birds, At-
lantic waters were similar to shelf-break and outer
shelf waters and North Sea waters to middle shelf
waters in the Bering Sea.
Joiris believed that in the Atlantic waters there is a
classical food chain with phytoplankton consumed by
herbivorous zooplankton, which are taken in turn by
carnivorous zooplankton, fish, and birds. In the
Pelagic distribution 713
North sea waters, in contrast, Joiris hypothesized that
the main recycling of nutrients is probably through
heterotrophic bacteria, with the consequence that
there is less food available to birds. The food chain
described for the Atlantic waters resembles that of
the outer shelf waters in the Bering, while that hy-
pothesized for the North Sea waters is similar to what
has been found in the middle shelf domain of the Be-
ring Sea (Section X of Volume 2).
Figs. 40-40 to 40-42 show density distributions for
all seabirds in spring, summer, and fall based on com-
bined ship and air surveys. It should be kept in mind
that these distributions are heavily weighted in favor
of shearwaters, and to a lesser extent in favor of ful-
mars and murres. Very little pattern can be detected
in the distribution of "all birds" for any season, prob-
ably because species differences tend to mask each
other when combined. There do seem to be two gen-
eral areas of low density. The first area includes the
shallow waters of Norton Sound south to just north
of Nunivak Island, and the west to the eastern ends of
St. Lawrence and St. Matthew islands. The second
area includes waters between the depths of 50 and
100 m in the extreme southeastern Bering Sea.
The distribution and abundance of marine birds in
the eastern Bering Sea is thus primarily based on the
rather complex interrelationships between available
Figure 40-40. Pelagic distribution of all species— air and
ship surveys: March-May.
Figure 40-41. Pelagic distribution of all species— air and
ship surveys: June-August.
Figure 40-42. Pelagic distribution of all species— air and
ship surveys: September-November.
714 - Marine birds
food, the location of adequate nesting sites, and the
physical and chemical characteristics of the ocean
water. The availability of food is likely to be the ulti-
mate determinant, but oceanographic conditions
usually control the occurrence and abundance of
food, and probably environmental cues such as sur-
face temperature determine where birds will concen-
trate their foraging efforts. Some species also appear-
to require a food source within a restricted distance
from nesting sites. The characteristics of surface wa-
ters and the location of nesting sites appear to direct-
ly affect species distribution patterns, while the abun-
dance and availability of food creates varying patterns
of density within the distribution.
ACKNOWLEDGMENTS
We thank G. Divoky, J. Guzman, and D. Woodby
for access to unpublished data, as well as the many
University of California, Irvine, and U.S. Fish and
Wildlife Service field assistants who served long hours
at sea taking data. Data management chores per-
formed by the data-processing groups at University of
California, Irvine, U.S. Fish and Wildlife Service, An-
chorage, and the Data Products Group at the Univer-
sity of Rhode Island were essential to the successful
production of the distribution maps. We benefited
greatly from discussions of bird biology in relation-
ship to physical and biological oceanography with the
following: H. Feder, L. Coachman, T. Cooney, W.
Drury, F. Favorite, T. Kinder, P. McRoy, M. Naugh-
ton, J. Schumacher, G. Smith, and C. Wallace. M.
Naughton carried the major responsibility for all Uni-
versity of California, Irvine, pelagic studies during
1978 and did much to pull together our efforts. The
following provided helpful comments on an earlier
version of this manuscript: D. Ainley, R. G. B.
Brown, J. Guzman, S. Hatch, and D. Wehle.
Logistic support was provided by the Juneau Proj-
ect Office and National Marine Fisheries, Pribilof Is-
land Program. We thank the officers and crew of the
NOAA vessels and of the R/V Moana Wave, who
aided our pelagic work, and in particular the heli-
copter pilots and crews from the NOAA ship Sur-
veyor. The officers and crew of the T.G. Thompson
provided valued help in 1978.
Partial financial support for the work was provided
by the Bureau of Land Management through inter-
agency agreement with the National Oceanographic
and Atmospheric Administration, under which a
multiyear program responding to needs of petroleum
development of the Alaskan continental shelf is man-
aged by the Outer Continental Shelf Environmental
Assessment Program (OCSEAP) Office. Support of
the National Science Foundation, Office of Polar Pro-
grams, to the PROBES study, J. Goering, Principal
Investigator, is gratefully acknowledged, as is NSF
grant DPP-7910386 to George Hunt.
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Shorebirds of the Eastern Bering Sea
Robert E. Gill, Jr., and Colleen M. Handel
U.S. Fish and Wildlife Service
Anchorage, Alaska
ABSTRACT
Largely on the basis of work conducted in western Alaska
since 1975, we present an overview of the shorebird resources
of the region and discuss their relationship to the littoral and
supralittoral habitats of the area. Thirty species of shorebirds
occur regularly and comprise an important component of the
eastern Bering Sea ecosystem. For a third of these species the
region supports the main Alaska population — for several spe-
cies, the main North American population. In winter and
spring littoral areas are generally ice-fast and little used by
shorebirds. After breeding, there is a pronounced movement
of shorebirds to coastal areas throughout the region. Popula-
tions regularly swell into the millions, many relying entirely on
littoral habitats while undergoing molt and premigratory fat
deposition. The extensive intertidal of the Yukon Delta and
lagoons of the Alaska Peninsula are used by more species, in
greater numbers, and for longer periods than other areas with-
in the region. The timing of fall migration shows considerable
variation by area, species, and age. The susceptibility of the
most common shorebird species to disturbances from petro-
leum development is discussed.
INTRODUCTION
The diversity and probably the numbers of shore-
birds (Charadrii) occurring in the eastern Bering Sea
region are unequalled in Alaska (Pitelka 1979), and
possibly even in North America, considered over a
comparable area at similar latitudes. Of the 68 spe-
cies of shorebirds known in Alaska, 52 occur in this
region (Kessel and Gibson 1978). Some 15 of these
are of Asiatic origin and straggle to Alaska in small
numbers each season. The majority, however, figure
prominently in the ecology of the region, particularly
during the summer and fall, when their numbers swell
into the millions over littoral and supralittoral habi-
tats of western Alaska. Furthermore, because Alaska-
produced shorebirds are highly migratory, many
having migratory paths encompassing several thou-
sands of miles, they become equally important to
areas along the Americas, Pacific archipelagoes, and
Asia.
Our knowledge of basic shorebird ecology and
behavior within Alaska has, until recently, been es-
sentially limited to that obtained on the breeding
grounds; little has been known about the require-
ments of shorebirds after breeding or during migra-
tion (Gill and Jorgensen 1979, Pitelka 1979). Since
1975, however, several studies in Alaska have been
devoted, wholly or in part, to determining the re-
quirements of shorebirds while they are along coastal
areas (Arneson 1978; Connors 1978; Senner and West
1978; Connors et al. 1979; Gill and Jorgensen 1979;
Isleib 1979; Schamel et al. 1979; Senner 1979;
Shields and Peyton 1979; Gill and Handel, unpub-
lished). These studies, while generally local in scope,
have greatly increased our understanding of such as-
pects of shorebird ecology as seasonal habitat use,
food requirements, numbers, and timing and patterns
of migration throughout Alaska.
A single systematic treatment of shorebirds in arc-
tic and subarctic environments in Alaska has yet to be
developed. We are able now, however, to treat
shorebirds on a regional basis. This chapter presents
such an overview of the shorebirds of the eastern
Bering Sea region.
We have divided the region into four major geo-
graphic areas (Fig. 41-1): Bristol Bay, extending
from the western tip of Unimak Island east and north
to Cape Newenham; the Yukon-Kuskokwim Delta
(hereafter called the Yukon Delta), from Cape
Newenham to Stuart Island; Norton Sound, from
Stuart Island to Cape Prince of Wales; and the large
Bering Sea islands, including the Pribilofs, Nunivak,
St. Matthew, and St. LawTence islands.
We have chosen to focus our discussion of shore-
birds in this region on their relationship to the littoral
719
120 Marine birds
Figure 41-1. Map of the eastern Bering Sea region.
or unvegetated intertidal as well as the vegetated in-
tertidal or supralittoral area affected by storm tides.
The amount of intertidal habitat and the number of
lagoons within each area are presented in King and
Dau (Fig. 42-1, Table 42-1, Chapter 42, this volume).
On the Yukon Delta the vegetated intertidal extends
inland several kilometers and includes much of the
nesting habitat of several species. If there is to be a
significant impact on shorebirds from petroleum de-
velopment in the eastern Bering Sea, it will most
likely come as a result of alteration of these critical
habitats.
Shurcbirds 721
DATA SOURCES
Basic information on shorebird distribution and
seasonal occurrence within the eastern Bering Sea re-
gion has come primarily from Gabrielson and Lincoln
(1959) and Kessel and Gibson (1978). Recent studies
throughout the region have provided further details.
Within Bristol Bay, information on shorebirds is avail-
able for the north central Alaska Peninsula (Gill et al.
1977, 1978; Gill 1979; Gill and Jorgensen 1979), up-
per Bristol Bay (Arneson 1978), and the Cape Newen-
ham-Peirce area (M. Dick and M. Petersen, Fish and
Wildlife Service, unpublished). On the Yukon Delta,
studies have been conducted by Holmes (1970,
1971a) and Holmes and Black (1973). Studies by
Connors (1978) and Shields and Peyton (1979) and
unpublished material from Heinrick Springer, of
Nome, Alaska, provide the basis for most information
presented for the southern Seward Peninsula and Nor-
ton Sound. In addition, we have relied heavily upon
our own unpublished material for information on
shorebirds of the Yukon Delta and Bristol Bay. Habi-
tat nomenclature for all areas follows that of Kessel
(1979).
RESULTS AND DISCUSSION
Habitat use
Probably the most extensive and diverse expanse of
intertidal habitat found along the Pacific coast of the
Americas occurs within the eastern Bering Sea region.
Only in the past few years have we begun to learn the
extent to which shorebirds are geographically and
temporally restricted in their use of this vast area.
Shorebirds use coastal habitats in the eastern
Bering Sea region in distinct seasonal patterns. In
spring, beginning in late April (Table 41-1), birds
move into the area after migrations which, in many
instances, began several thousand miles to the south.
Many have come from the Copper River Delta in the
northern Gulf of Alaska and from Kachemak Bay in
lower Cook Inlet (Isleib 1979, Senner 1979). The
intertidal habitats of these areas are generally ice-free
in spring and are used as refueling stops by millions of
shorebirds before they proceed to nesting grounds in
western and northern Alaska.
Upon their arrival in the eastern Bering Sea area,
shorebirds usually find that littoral habitats are ice-
fast and little intertidal is available for foraging. Only
along the western Alaska Peninsula, portions of Bris-
tol Bay, and the mouths of major rivers to the north
are littoral areas usually ice-free in spring. These are
used by Rock Sandpipers (Calidris ptilocnemis). Bar-
tailed Godwits (Limosa lapponica). Red Knots (C.
canutus), American Golden Plovers (Ptuuialis domin-
ica), and Black-bellied Plovers (P. squatarola) for
several days or weeks before they move to their
breeding grounds (Gill and Handel, unpublished). It
is not known what portion of their respective popula-
tions uses these areas in spring. Nearshore waters of
the region are also used in spring by Red and North-
ern Phalaropes (Phalaropus fulicarius and P. lobatus).
Large rafts of these species form in spring but infor-
mation on their distribution and movements is frag-
mentary (Gabrielson and Lincoln 1959).
After spring migration, shorebirds settle on the
nesting grounds and make little use of littoral areas
from late May through June. Throughout the region
the coastal fringe provides important shorebird nest-
ing habitat, particularly for eight species: Semi-
palmated Plover (Charadrius semipalmatus). Black
Turnstone (Arenaria melanocephala). Long- and
Short-billed Dovdtcher (Limnodromus scolopaceus
and L. griseus). Red and Northern Phalarope, Semi-
palmated Sandpiper (Calidris pusilla), and Dunlin (C.
alpina). In terms of numbers of birds, the principal
shorebird nesting area within the region is the Yukon
Delta. Here, the highest shorebird nesting densities
are found in low-lying coastal areas, which are flood-
ed by tides occasionally during the nesting season and
more regularly in early spring and late fall.
After nesting, shorebirds tend to move to coastal
areas, particularly to littoral habitats (Table 41-2).
This marked shift has been noted in shorebird popula-
tions from Pt. Barrow to the western Alaska Penin-
sula (Connors 1978, Connors et al. 1979, Gill and
Jorgensen 1979, Shields and Peyton 1979). As sug-
gested by Holmes (1970), Myers and Pitelka (MS),
and others, this movement may be in response to a
deterioration in feeding conditions on the nesting
grounds and a corresponding improvement on littoral
habitats.
The areas within the region most intensively used
for foraging by postbreeding shorebirds include the
lagoons along the southern Seward Peninsula and
eastern Norton Sound, the extensive intertidal flats of
the central Yukon Delta, and the lagoons of the Alas-
ka Peninsula. These key areas, rich in benthic organ-
isms, are adjacent to the nesting areas. Of them, the
intertidal of the Yukon Delta is used by more species,
in greater numbers, and in higher densities than any
other littoral area of the region (Table 41-3, Fig. 41-
2). This may, in part, be due to a richer benthos on
the delta, or to proximity to a more extensive and
productive nesting area. For reasons not yet under-
stood, the expansive intertidal of northern Bristol
Bay is not extensively used by shorebirds in fall.
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723
TABLE 41-2
Habitat use by shorebirds in late summer and fail in the eastern Bering Sea region.
Adults
Postfledging j
uveniles
Norton
Yukon
Bristol
Bering
Norton
Yukon
Bristol
Bering
Species
Sound
Delta
Bay
Sea Is.
Sound
Delta
Bay
SeaL
American Golden Plover
L-^T
T
L
T
L+T
L+C
L
T
Black-bellied Plover
-
T
L
—
—
L+C
L
—
Hudsonian Godwit
T+L
T+L
—
—
T+L
T+L
—
—
Bar-tailed Godwit
T+L
L+T
L
T+L
T+L
L+T
L
T+L
Whimbrel
T+L
T+L
L+C
—
T+L
T+L
L+C
—
Bristle-thighed Curlew
—
C+T
—
—
—
C+T
—
—
Ruddy Turnstone
L
T
L
T+L
L
T+L
L
T+L
Black Turnstone
L+C
L
L
—
L+C
L
L
—
Northern Phalarope
C+L
C+L
L
L+T
C+T
L+C
L
L+T
Red Phalarope
C+L
C+L
L
L+T
L
L
L
L+T
Short-billed Dowitcher
—
—
L
—
—
—
L
—
Long-billed Dowitcher
T+L
C
L
—
L+T
C+L
L
—
Red Knot
L
L
—
—
L
L
—
—
Sanderling
-
—
L
L
L
L
L
L
Semipalmated Sandpiper
L
C
-
-
L+C
0
—
—
Western Sandpiper
L+T
L
L
—
L+T
L
L
—
Least Sandpiper
T
—
L+C
—
T
—
L+C
—
Pectoral Sandpiper
L
—
-
—
L+C
C
—
C
Sharp-tailed Sandpiper
—
—
L
L
L+C
L+C
L
L
Rock Sandpiper
L
L
L
L
L
L
L
L
Dunlin
L
L
L
—
L+C
L+C
L
—
L = littoral, C = coastal wet meadows, T = tundra (dwarf shrub meadows and dwarf shrub mat).
The sequence within a couplet indicates primary and secondary use, although in some instances both are used equally.
Within the eastern Bering Sea region, patterns of
seasonal use of littoral areas by shorebirds appear to
be similar (Fig. 41-2). These patterns are thought to
reflect differences in migrational timing among spe-
cies as well as between sexes and age groups of par-
ticular species (Table 41-2). At Wales, Yukon Delta,
and Nelson Lagoon there is a buildup in late July and
early August primarily of Western Sandpipers (C.
mauri), followed in September by an even greater
buildup of Dunlin (Fig. 41-2). Similar peaks reflect-
ing passages of plovers, godwits, dovntchers, and
phalaropes occur at each site, but their magnitudes
are smaller (Table 41-3, species accounts).
The duration of use and the numbers of shorebirds
supported per unit of littoral habitat in the region ap-
pear greatest along the Alaska Peninsula and on the
Yukon Delta (Table 41-3, Fig. 41-2). To the north,
in Norton Sound and along the Chukchi and Beaufort
sea coasts, shorebirds tend to use littoral areas for
shorter periods (Connors 1978, Connors et al. 1979,
Schamel et al. 1979), perhaps in response to the
shortness of the seasons. However, recent informa-
tion (Gill and Handel, unpublished) suggests that for
species such as American Golden Plovers, Bar-tailed
Godwits, Red Knots, and Dunlin, large segments of
the population are leaving or moving through these
areas well before the onset of fall. Most appear to
move south to the Yukon Delta and lagoons of the
Alaska Peninsula. Here they often remain for several
weeks before migrating to their respective winter
quarters.
Our discussion so far has primarily focused on the
importance of littoral areas as foraging areas for post-
breeding shorebird populations. Throughout the re-
gion littoral and suprahttoral habitats are also critical
as roosting areas. On the Yukon Delta the larger
birds such as Bar-tailed Godwits and Red Knots gen-
erally roost 2-5 km inland on dwarf shrub meadow
and mat tundra, returning at each low tide to forage
on the outermost mudflats (Gill and Handel, unpub-
lished). Occasionally when high tides are particularly
low, these species may roost on exposed dry flats.
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WALES
(65°40'n)
YUKON DELTA
(61°10'n
NORTON SOUND
(65°n)
NELSON LAGOON
15
1
15
JULY
AUGUST
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SEPT
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JULY
1 15
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15
Figure 41-2. Total shorebird densities over littoral habitats at four study sites in the eastern Bering Sea region. Data at Wales
from Connors (1978); Norton Sound, Shields and Peyton (1979) and unpublished; Yukon Delta, Gill and Handel, unpub-
lished; and Nelson Lagoon, Gill and Jorgensen (1979) and unpublished.
The smaller sandpipers, particularly Dunlin, Western
Sandpipers, and Rock Sandpipers, generally roost
along the littoral-vegetation interface, usually flying
from 1 to 3 km to feeding areas. Species of both
groups appear to remain faithful to both feeding and
roosting areas, at least well into molt and early stages
of fat deposition, and probably until migration (Gill
and Handel, unpublished). On the Alaska Peninsula,
most shorebirds roost in littoral or supralittoral areas
(Gill, unpublished).
In winter there is little use of the eastern Bering
Sea region by shorebirds because littoral areas be-
come ice-fast and unavailable for foraging. Only in
Bristol Bay, along the ice-free western Alaska Penin-
sula, can wintering shorebirds be found regularly.
Here relatively low numbers of Rock Sandpipers oc-
cur on rocky shores and gravelly beaches, and Sander-
lings (Calidris alba) on sand and mud-sand substrates.
Migration
The shorebirds of the eastern Bering Sea engage in
some of the most varied and highly specialized migra-
tions among birds, many involving sex- and age-
related differences, both in timing and in the routes
used. Shorebird migration over western Alaska is a
pronounced seasonal phenomenon: the spring migra-
tion is distinctly different from that in fall. Spring
migration can be characterized as short and direct,
often occurring during a period of a few weeks, usu-
ally in mid- to late May. Once along west and north
coastal Alaska, most species move directly to the
breeding grounds. In several of the calidridine sand-
pipers, and probably in many other species, males
generally precede females to the nesting areas, but
seldom by more than a few days (Holmes 1966,
1971a; Ashkenazie and Safriel 1979; Gill and Handel,
unpublished).
726 Marine birds
Fall migration is more protracted, often beginning
in late June and continuing through September and
into October for some species (Table 41-3). Shore-
birds nesting in the eastern Bering Sea region usually
follow one of two general fall migration patterns: in
the first, both adults and juveniles quickly leave the
nesting grounds. They may then proceed on a very
rapid migration, like Semipalmated Sandpipers, which
seldom frequent intertidal areas of the region; or they
may leisurely move south, like Western Sandpipers
and Black Turnstones, which move to intertidal areas
but do not remain in the region to molt (Holmes
1972; Gill and Handel, unpublished).
The second basic pattern is typical of most species
of the region. Both adults and juveniles move to
coastal areas for prolonged periods, generally building
lipid stores necessary for extended migrations. Many
also complete their prebasic molt before departing for
wintering grounds. We do not know what portions of
the large numbers of post-breeding birds using Bering
Sea coastal areas are from adjacent nesting grounds,
and what portion come from further north. In Bris-
tol Bay, large numbers of several species stage on la-
goons of the north central Alaska Peninsula (Gill and
Jorgensen 1979), well south of their breeding range.
These include the Bar-tailed Godwit, Whimbrel (Nu-
menius phaeopus). Ruddy Turnstone (Arenaria
interpres), and Long-billed Dowitcher, which breed
on the Yukon Delta and north. In coastal areas of
the Yukon Delta and Norton Sound, birds from more
northern breeding grounds may be mixing with those
from local populations.
Within a species, timing of migration may vary by
sex and by age. For example, female Western Sand-
pipers and Black Turnstones depart slightly before
males (Gill and Jorgensen 1979; Gill and Handel, un-
published), but male Pectoral Sandpipers (C. mela-
notos) depart before females (Pitelka 1959). Such
differences in timing of migration are thought to be
linked to differences in social systems (Pitelka et al.
1974).
Age-related differences in migrational timing are
often much more pronounced. Juveniles of species
such as the plovers, turnstones, phalaropes, and West-
em, Least (C. minutilla), and Pectoral Sandpipers
often depart several weeks later than adults (Pitelka
1959; Holmes 1972; Gill and Handel, unpublished).
In species which remain to molt, such as Dunlin and
Rock Sandpipers, most adults and juveniles leave
together (Gill and Jorgensen 1979; Gill and Handel,
unpublished). Bar-tailed Godwits staging on the
Alaska Peninsula appear to depart as family groups
(Gill and Jorgensen 1979).
Perhaps the most interesting case of age-segregated
migration is that of the Sharp-tailed Sandpiper (C.
acuminata), which nests in Siberia and winters in the
South Pacific. Large populations occur along the
eastern Bering Sea coast each fall, but they are almost
exclusively juveniles (GUI and Handel, unpublished).
The reasons for this striking segregation are not yet
understood.
Feeding
Among arctic and subarctic nesting birds, food is
probably the single most important factor regulating
population numbers, timing of breeding, and habitat
use. Holmes (1970, 1971a) addressed these relation-
ships for Dunlin and Western Sandpipers on the Yu-
kon Delta during the nesting period. There is little
published information, however, on the feeding ecol-
ogy of shorebirds during their use of Bering Sea
coastal areas before or after nesting. What little is
available is about shorebirds on the Pribilof Islands
in late summer (Preble and McAtee 1923, Thompson
1973).
Senner and West (1978) have demonstrated the nu-
tritional significance of littoral habitats for shorebirds
migrating through the north Gulf of Alaska in spring,
particularly as these areas relate to levels of lipid and
mineral intake thought necessary to initiate breeding
activities. This phenomenon of nutritional "re-
charging" probably accounts in part for shorebird use
of Bering Sea intertidal habitats in spring. Indeed,
most of the species which use these areas in spring
have completed very extensive, energy-demanding,
nonstop migrations (see species accounts).
During nesting, it appears that dipteran larvae of
the families Chironomidae, Tipulidae, and Muscidae
are the staples in the diets of most shorebirds breed-
ing in coastal fringe habitats (Holmes 1970; Gill and
Handel, unpublished). Feeding requirements of
shorebirds after breeding are not well known, but the
bivalve Macoma balthica figures prominently in the
diets of several species throughout the region (Gill
and Handel, unpublished). Also important, especially
on the Yukon Delta, are dipteran larvae of the family
Ephydridae (Gill and Handel, unpublished).
SPECIES ACCOUNTS
We present here annotated accounts of the 30 most
common shorebird species occurring in the eastern
Bering Sea region. In each account, we discuss, as
data permit, the occurrence, habitat use, and migra-
tional timing of that species over the four geographic
areas of the region.
Shorebirds 727
I
Semipalmated Plover (Charadrius semipalmatus)
This small plover occurs along the coast of the
eastern Bering Sea region during the breeding season
and in migration. It generally nests in small numbers
in the supralittoral zone on sand beaches, dunes, or
bars (Gabrielson and Lincoln 1959, Holmes and
Black 1973, Gill and Jorgensen 1979). In Bristol
Bay, where it is a common breeder, nests have also
been found in wet and dwarf shrub meadows (M.
Dick, impublished). There are breeding records for
this species on all large Bering Sea islands except the
Pribilofs (Gabrielson and Lincoln 1959, Thompson
1967, DeGange and Sowls 1978).
In migration, the Semipalmated Plover forages
singly or in small flocks along sandy beaches and
mudflats throughout the region. At the head of Nor-
ton Sound, it also frequents wet and dwarf shrub
meadows (Gabrielson and Lincoln 1959, Shields and
Peyton 1979). Spring migrants move through the re-
gion from late April to mid-May, with most settling
directly on their nesting areas (Gabrielson and Lin-
coln 1959; Gill and Jorgensen 1979; M. Dick, unpub-
lished; Gill and Handel, unpubUshed). Fall migrants
spend more time on littoral areas, particularly in Bris-
tol Bay, with adults moving through in July and ju-
veniles from early August through mid-September.
(Gill and Jorgensen 1979; M. Dick, unpublished).
One fall record exists from St. Paul Island (Gabrielson
and Lincoln 1959).
American Golden Plover (Pluuialis dominica)
This bird nests on drier tundra of the eastern
Bering Sea region from Cape Prince of Wales south to
the Kuskokwim River area, as well as on St. Lawrence
and Nunivak islands (Gabrielson and Lincoln 1959).
Spring migration is fairly rapid and direct through
the eastern Bering Sea region, with some birds stop-
ping on the Pribilof Islands (Gabrielson and Lincoln
1959) and a few throughout Bristol Bay (Gill and
Jorgensen 1979; M. Dick, unpublished). Spring mi-
grants use both intertidal flats and tundra, but appear
to favor tundra. During fall migration, large concen-
trations of both adults and juveniles occur along
coastal mudflats, intertidal sloughs, and rivers
throughout the region, although an unknown percen-
tage remains on wet meadows. Fall movement
through the northern Bering Sea area persists from
July through September, peaking in early September
(Fay and Cade 1959, Connors 1978, Shields and Pey-
ton 1979). From the Yukon Delta south, a wave of
migrants passes through progressively later, with the
last birds gone from the Alaska Peninsula and the
PribUofs by late October (Gabrielson and Lincoln
1959; Gill et al. 1977, 1978; Gill and Jorgensen
1979). The first fall migrants have been noted in
wintering areas in the central Pacific in late July
(Johnston and McFarlane 1967). Adults appear to
precede juveniles in this migration.
Black-bellied Plover (Pluuialis squatarola)
This plover nests over dwarf shrub meadows of the
major river deltas along the arctic coast and south to
the Yukon Delta (Gabrielson and Lincoln 1959).
During both spring and fall migration, it is found
along the coast, frequenting mudflats and wet mead-
ows. In spring. Black-bellied Plovers are fairly com-
mon along upper Bristol Bay (Arneson 1978; M.
Dick, unpublished). However, the fact that they are
uncommon farther out along the Alaska Peninsula
(Gill and Jorgensen 1979) indicates that their migra-
tion route may take them across the base of the pen-
insula from the Gulf of Alaska. North of Bristol Bay
there is little use of littoral areas by this species in
spring.
Beginning in late summer, adults and juveniles
move to intertidal mudflats throughout most of the
region. In Norton Sound, Black-bellied Plovers are
uncommon on mudflats of eastern Norton Bay
(Shields and Peyton 1979) and seldom use lagoons
along the southern Seward Peninsula (H. Springer,
personal communication). On the Yukon Delta, how-
ever, thousands of adults pass through from late June
to early August, with even larger numbers of juveniles
appearing from early August through mid-September
(Gill and Handel, unpublished). In upper Bristol Bay,
passage occurs slightly later, with adults moving
through from late June to early September and juven-
iles from late August to late September (M. Dick, un-
published). Along the Alaska Peninsula, this species
is again uncommon, seen primarily in October in
small numbers, but occasionally in flocks of 30-50
birds (Gill et al. 1977, 1978; Gill and Jorgensen
1979). The Black-bellied Plover is a very rare migrant
to the Pribilof Islands and St. Lawrence Island in
both spring and fall (Kessel and Gibson 1978).
Hudsonian Godwdt (Limosa haemastica)
During most of its stay in Alaska, this species is
generally associated with inland habitats (Gabrielson
and Lincoln 1959, Kessel and Gibson 1978), although
in the northern part of the region, small numbers reg-
ularly use littoral habitats during fall migration.
Within the Norton Sound area, this bird apparently
prefers dwarf shrub meadows (Shields and Peyton
1979), but it has been recorded on mudflats at Koy-
uk and Buckland (B. Kessel, Univ. of Alaska, personal
communication). Jones and Kirchhoff (Fish and Wild-
life Service, unpublished) report that haemastica are
728 Marine birds
abundant on the tide flats on the north Yukon Delta,
in July. Records of Hudsonian Godwits along the
coast become increasingly scarce farther south (Kes-
sel and Gibson 1978). On the southern Yukon Delta,
there appears to be a regular but comparatively small
movement of birds from late June through August,
but birds are seldom found near the coast (C. Dau,
FWS, unpublished; Gill and Handel, unpublished).
Bar-tailed God wit (Limosa lapponica)
This godwit is the most abundant of the large
shorebirds breeding in or migrating over vifestern Alas-
ka. The main nesting concentration occurs on the
Yukon Delta, but the species breeds north to the Col-
ville Delta (Gabrielson and Lincoln 1959). The Bar-
tailed Godwit vidnters primarily in the southwest
Pacific.
In spring, birds arrive along the west coast of Alas-
ka beginning in early May. Most probably move di-
rectly to the nesting grounds, although in years of
heavy snow cover, a substantial number of godvidts
linger on adjacent intertidal areas before moving in-
land. Use of the littoral zone in spring is more pro-
nounced at Norton Sound (H. Springer, personal
communication) and on the Yukon Delta (C. Dau,
unpublished; Gill and Handel, unpublished) than at
Bristol Bay (Arneson 1978, Gill and Jorgensen 1979).
Beginning in late June, the Bar-tailed Godvidt be-
comes one of the more conspicuous shorebirds on the
mudflats of the Yukon Delta. Adults generally
precede juveniles in their movement to the coast after
breeding (Gill and Handel, unpublished). In Norton
Sound, birds reach peak populations in mid- August
and maintain their numbers into early September
(Shields and Peyton 1979; H. Springer, personal
communication). On the Yukon Delta, populations
of adults peak in late July, but juveniles are most
abundant in late August (Dau, unpublished; Gill and
Handel, unpublished). By mid-September, most of
the godwits have left the delta. On the Alaska Penin-
sula, this species does not begin to build in numbers
until early September, reaching a peak in mid-
September. Birds have usually departed from the la-
goons by late September (Gill et al., 1977, 1978; Gill
and Jorgensen 1979). It is likely that these birds have
molted on the Yukon Delta or elsewhere and then
moved to the lagoons of the peninsula to fatten
before migration. The comparatively low num-
bers of godv^dts seen in fall on the Bering Sea islands
(Gabrielson and Lincoln 1959) and in the Aleutians
(Byrd et al. 1974) suggest that most depart directly
from the mainland of western Alaska, probably from
the Yukon Delta and Alaska Peninsula (Gill and
Jorgensen 1979), to fly directly overseas to the south-
west Pacific.
Whimbrel (Numenius phaeopus)
According to Gabrielson and Lincoln (1959), the
Whimbrel probably breeds from the mouth of the
Kuskokwim River, both along the coast and over the
interior, north to the Canadian Arctic. There are no
breeding records from the Alaska Peninsula or Bering
Sea islands.
Spring migrants moving into Alaska generally pro-
ceed directly to the nesting grounds. During the sum-
mer and fall, Whimbrels rely on littoral areas to vary-
ing degrees. In eastern Norton Sound, Whimbrels
were found to favor intertidal areas over adjacent tun-
dra habitats (Shields and Peyton 1979, unpublished).
Along the southern Seward Peninsula, Whimbrels in
flocks of 200 or more have been seen roosting on
mudflats of Safety Lagoon in September (H. Spring-
er, personal communication). On the Yukon Delta,
phaeopus commonly occur along the intertidal of
rivers and sloughs as well as on the extensive mud-
flats, where they often associate with Bar-tailed God-
wits (Dau, unpublished; Gill and Handel, unpub-
lished). But the majority of the birds prefer to
remain inland on wet and dwarf shrub meadows. In
northern Bristol Bay at Nanvak Bay, Whimbrels occur
regularly in fall in flocks of 20-30 birds, many using
mudflats and rocky shores (M. Dick, unpublished).
On the Alaska Peninsula, Whimbrels occur in unusu-
ally large flocks. At Naknek, a flock of over 500 was
seen in early July 1969 (D. Gibson, Univ. of Alaska,
personal communication); and at Nelson Lagoon,
from late June through August, flocks of as many as
1,000 birds have been observed foraging on the mud-
flats (Gill et al. 1977, Gill and Jorgensen 1979).
Bristle-thighed Curlew (Numenius tahitiensis)
This species is unique among Alaska shorebirds be-
cause its breeding range remains an enigma. Only two
nests have been found, these in 1948 on bare tundra
in the Nulato Hills (Allen 1948, Allen and Kyllingstad
1949). Other reports (H. Springer, personal commu-
nication) suggest that the highlands of the Seward
Peninsula are also used for nesting.
The comparatively few spring records along coastal
Alaska suggest that this species moves directly to its
breeding grounds from wintering areas on islands in
the south central Pacific. These birds appear on
coastal wet and dwarf shrub meadows on the Yukon
Delta in early July (Gill and Handel, unpublished),
and fatten preparatory to their fall transoceanic
migration. These curlews rarely use littoral areas on
the delta, and they remain scattered in flocks seldom
Shorebirds
729
exceeding 20 birds. Away from the Yukon Delta,
this species is uncommon in fall. There are reports of
Bristle-thighed Curlews with Whimbrels at Cape
Newenham (M. Dick, unpublished) and of occasional
flocks in upper Bristol Bay and on the Bering Sea
islands (Gabrielson and Lincoln 1959). Birds are
generally gone from western Alaska by late August.
Greater Yellowlegs (Tringa melanoleuca)
This wader breeds in wet inland bogs of south
central and southeastern Alaska, and perhaps sparing-
ly on the eastern Alaska Peninsula (Gabrielson and
Lincoln 1959; D. Gibson, personal communication).
During migration, the Greater Yellowlegs can be
found in coastal areas on the Yukon Delta and Bris-
tol Bay, frequenting wet meadows and sometimes
mudflats. Spring migration through this area extends
from late April to late May, with small numbers pass-
ing through upper Bristol Bay and a very few along
the Yukon Delta (Gabrielson and Lincoln 1959; M.
Dick, unpublished; Gill and Handel, unpublished).
There are two spring records for this species from the
Pribilof Islands (D. Gibson, personal communication).
During fall migration, numbers increase both on the
delta and throughout Bristol Bay, with birds some-
times making extensive use of mudflats, particularly
on the Alaska Peninsula (Gill and Jorgensen 1979;
Gill, unpublished). Along coastal Yukon Delta,
Greater Yellowlegs occur regularly, usually as single
birds, from early August to late September (Gill and
Handel, unpublished). Throughout Bristol Bay they
become fairly common, occurring in small flocks
from early July to mid-October (Gill and Jorgensen
1979; M. Dick, unpublished). There is one historical
record of this species on the Pribilof Islands in fall
(Gabrielson and Lincoln 1959).
Lesser Yellowlegs (Tringa flavipes)
This smaller yellowlegs also breeds in bogs of in-
terior Alaska, but is much less common than the
Greater Yellowlegs along the coast of the eastern
Bering Sea. The Lesser Yellowlegs apparently moves
directly to the breeding grounds in spring without
using littoral areas in this region. In the fall, it is a
rare migrant in Norton Sound, frequenting brackish
ponds, mudflats, and dwarf shrub meadows (Shields
and Peyton 1979). Farther south it is seen more fre-
quently as a regular and common migrant over wet
meadows along the north Alaska Peninsula from mid-
July to early October (Gill and Jorgensen 1979). It is
a rare fall straggler to the Pribilof s (Kenyon and
Phillips 1965) and St. Lawrence Island (Thompson
1967).
Wandering Tattler (Heteroscelus incanus)
This shorebird has been found breeding along gra-
velly streams in mountainous areas throughout south-
coastal, central, and western Alaska (Gabrielson and
Lincoln 1959, Kessel and Gibson 1978). In migra-
tion, however, it prefers rocky shores and steeply cut
riverbanks along the coast. The small numbers of
tattlers found in littoral areas during migration are
probably from suitable nesting areas in adjacent habi-
tat. In spring, Wandering Tattlers occur on the Yu-
kon Delta in late May (Gill and Handel, unpublished)
and in northern Bristol Bay between mid-May and
mid-June (M. Dick, unpublished). In fall, they be-
come more widespread, but remain uncommon
throughout the region from mid-July through late
September (Gabrielson and Lincoln 1959, Kessel and
Gibson 1978). There are many records of this species
on the Bering Sea islands in fall, but only one in
spring, on St. Paul Island.
Ruddy Turnstone (Arenaria inter pres)
This bird is a common breeder in the dwarf shrub
meadows along the Bering Sea coast as far south as
the Yukon Delta and on St. Lawrence Island (Gabriel-
son and Lincoln 1959). A few historical breeding
records exist for St. Matthew and St. Paul islands.
During spring migration, there is little use of littoral
areas along the western Alaska coast. Small numbers
trickle through Bristol Bay and the Yukon Delta
throughout May; there is no significant movement
through Norton Sound or on the Bering Sea islands
(Gabrielson and Lincoln 1959; Gill and Jorgensen
1979; M. Dick, unpublished; Gill and Handel, unpub-
lished).
Fall movements extend from mid-July to early
October through western Alaska, with adults pre-
ceding juveniles. On the Pribilof Islands, spectacular
concentrations of tens of thousands of migrant turn-
stones are found in late summer and fall. At least
some of these birds are coming from breeding
grounds in Siberia and St. Lawrence Island (Thomp-
son 1973). After staging on the Pribilofs, they depart
on a transoceanic route, which takes them through
the central Pacific in fall, returning to the breeding
grounds in spring along the western Pacific via Japan
and perhaps the Commander Islands (Thompson
1973). It is not known if interpres that breed on the
north and west coasts of mainland Alaska follow this
route or if they winter along the Pacific coast of the
Americas.
Nowhere on the mainland of western Alaska do
interpres occur in numbers similar to those on the
730 Marine birds
Pribilofs. In the Norton Sound area, they are un-
common fall migrants at Cape Prince of Wales (Con-
nors 1978), are widespread but uncommon at Safety
Lagoon (H. Springer, personal communication), but
apparently do not occur at the head of Norton Bay
(Shields and Peyton 1979). Along the Yukon Delta
small flocks of tumstones occur regularly on upper
tidal flats from mid-July through mid-September (Gill
and Handel, unpublished). South of the Yukon Delta
they are uncommon fall migrants in north Bristol Bay
(M. Dick, unpublished), but become common along
the rocky shores and mudflats of the north central
Alaska Peninsula (Gill and Jorgensen 1979; Gill, un-
published). On the peninsula, turnstones first appear
in mid-July and populations peak in late August.
Most have passed through the area by early October.
The Ruddy Turnstone is a fairly common fall migrant
on St. Lawrence and St. Matthew islands (Fay and
Cade 1959, Gabrielson and Lincoln 1959, DeGange
and Sowls 1978).
Black Turnstone (Arenaria melanocephala)
The Black Turnstone is primarily a bird of the Yu-
kon Delta, yet occurs as a regular breeding species
north to Cape Prince of Wales and south through Bris-
tol Bay and along the Alaska Peninsula (Murie 1959,
Kessel et al. 1964, Harris 1966, Holmes and Black
1973, Gill and Jorgensen 1979). In spring, birds
move directly to the breeding grounds, usually in
early May. On the Yukon Delta, nests are concen-
trated on coastal wet and salt grass meadows and are
subject to occasional flooding from storm-driven tides
(Gill and Handel, unpublished).
After the young hatch, usually from early to mid-
June, adults begin to shift their foraging from vege-
tated areas to the adjacent intertidal zone. As young
fledge, adults begin flocking on the mudflats and, by
mid-July, most have left the delta. Adults presum-
ably migrate directly to areas in the Gulf of Alaska
and southeast Alaska, where they probably molt be-
fore flying to wintering areas. Juvenile tumstones ap-
pear in small groups on the mudflats of the Yukon
Delta beginning in early August and are present into
early September. In Norton Sound and Bristol Bay,
juveniles appear in late August, but usually as single
birds (Gill and Jorgensen 1979; H. Springer, personal
communication; M. Dick, unpublished).
Northern Phalarope (Phalaropus lobatus)
The breeding range of this shorebird is probably
more extensive than any other wathin Alaska (Ga-
brielson and Lincoln 1959). It breeds throughout the
eastern Bering Sea region, including St. Lawrence and
St. Matthew islands. Birds generally arrive through-
out western Alaska from mid- to late May and, de-
pending on ice and snow conditions, may move
directly to the nesting grounds. In late springs, par-
ticularly in Norton Sound, large rafts of lobatus fre-
quently congregate along open ice leads (H. Springer,
personal communication). In summer, birds begin
flocking in Norton Sound in early July, and usually
pass through the area by late August (Shields and
Peyton 1979). On the Yukon Delta, adults occur in
large numbers on nearshore waters, mudflats, and
salt grass meadows during mid -July. The peak pas-
sage of juveniles occurs from mid -August through
mid-September (Gill and Handel, unpublished).
Northern Phalaropes exhibit similar timing in their
movements through Bristol Bay and along the Alaska
Peninsula (Gill et al. 1977, 1978; Gill and Jorgensen
1979; M. Dick, unpubUshed).
Red Phalarope (Phalaropus fulicarius)
The Red Phalarope nests throughout the region
from northern Bristol Bay to Norton Sound, includ-
ing St. Lawrence Island (Gabrielson and Lincoln
1959). In Norton Sound, it occurs regularly in late
May, sometimes in rafts of several thousands (H.
Springer, personal communication). On the Yukon
Delta and on St. Paul and St. Matthew islands, birds
generally arrive from mid- to late May (Gabrielson
and Lincoln 1959; Dau, unpublished; Gill and Han-
del, unpublished). In these areas, large numbers of
birds are often present in littoral habitats until early
June before settling onto the nesting grounds.
Throughout Bristol Bay this species is an uncommon
spring migrant, occurring at Cape Newenham from
mid- to late May (M. Dick and M. Petersen, FWS, un-
published) and along the Alaska Peninsula in mid-May
(Gill and Jorgensen 1979).
In Norton Sound, Red Phalaropes make little use
of littoral areas after breeding or during fall migration
(Connors 1978; Shields and Peyton 1979; H. Spring-
er, personal communication). Over the Hooper/
Hazen Bay segment of the Yukon Delta, Gabrielson
and Lincoln (1959) reported the Red Phalarope abun-
dant in early August. However, in 1978 and 1979,
only small, scattered flocks consisting mainly of ju-
veniles were seen over this same area, and only during
July and early September were movements noted
(Gill and Handel, unpublished). In Bristol Bay, birds
have been reported from late June through late Octo-
ber. Here, Bartonek and Gibson (1972) found many
small flocks scattered at sea in July. At Nelson La-
goon, numbers of adults peaked in mid-July, never
exceeding 50 birds (Gill et al. 1977, Gill and Jorgen-
sen 1979).
Shorebirds 731
Common Snipe (Gallinago gallinago)
The Common Snipe breeds throughout western
Alaska, but generally away from littoral areas, and
usually in very low densities (Gabrielson and Lincoln
1959). This species is one of the earliest spring mi-
grants: birds appear in late April over much of the
Norton Sound, Yukon Delta, and Bristol Bay. In fall,
birds generally migrate directly from the breeding
grounds.
Short-billed Dowitcher (Limnodromus griseus)
Of the two species of dowitcher breeding in the
eastern Bering Sea region, griseus has the more re-
stricted nesting distribution, being limited to the
Alaska Peninsula and upper Bristol Bay, perhaps oc-
curring as far north as Goodnews Bay (Gabrielson and
Lincoln 1959, Gill et al. 1977, Gill and Jorgensen
1979). In spring, birds arrive in the region in mid-
May and move directly to the breeding grounds. Post-
breeding flocking begins in late June, as birds move
from wet meadows to adjacent intertidal areas.
Flocks gradually increase in size, often comprising
several thousand birds, and generally remain through
early August (Gill and Jorgensen 1979). The Short-
billed Dowitcher is usually gone from western Alaska
by mid-September.
Long-billed Dowitcher (Limnodromus scolopaceus)
The more common of the two dowitchers in Alas-
ka, scolopaceus breeds from the mouth of the Kusko-
kwdm River north along the coast and inland to the
Yukon Territory (Gabrielson and Lincoln 1959).
Among the Bering Sea islands, only St. Lawrence is
knowai as a breeding site (Fay and Cade 1959). The
species also breeds across the Bering Strait on the
Chukotsk Peninsula (Dementyev and Gladkov 1951).
Long-billed Dowitchers move directly to the breed-
ing grounds in spring, and are considered to be among
the latest migrants of western Alaska shorebirds.
They generally do not arrive in the Norton Sound
area until early June (H. Springer, personal communi-
cation) and not until late May on the Yukon Delta
(Holmes and Black 1973; Dau, unpublished; Gill and
Handel, unpublished). In summer, adults, followed
by juveniles, begin using littoral habitats, mostly
along major rivers. The majority of the population,
however, remains inland until fall migration (Shields
and Peyton 1979; Gill and Handel, unpublished).
Postbreeding birds peak in number in Norton Sound
and on the Yukon Delta in early September. Begin-
ning mid-August, there is an influx of scolopaceus at
Nelson Lagoon and probably other estuaries along the
Alaska Peninsula (Gill and Jorgensen 1979; Gill, un-
published). These birds generally do not peak in
numbers until early October, well after numbers have
begun to decline farther north, suggesting that the
Alaska Peninsula is used as part of the regular fall mi-
gration route.
Surfbird (Aphriza virgata)
This species is a rare spring and fall migrant along
the coast of the eastern Bering Sea. The few breeding
records available indicate that it probably nests in
most of the mountainous areas of mainland Alaska,
concentrating in the ranges of the interior (Gabrielson
and Lincoln 1959, Kessel and Gibson 1978). The few
Surfbirds using littoral areas of the region probably
nest in suitable adjacent habitat, e.g., the mountains
surrounding Norton Sound, the Kilbuck Mountains of
northern Bristol Bay, and the Aleutian Range of the
Alaska Peninsula.
Red Knot (Calidris canutus)
The habits of this large sandpiper in Alaska are
poorly known. There are relatively few breeding
records, and its migration routes are not well known
(Gabrielson and Lincoln 1959, Kessel and Gibson
1978). The most recent information indicates that
within Alaska canutus breeds in the mountainous re-
gions of the Seward Peninsula, over the western
Brooks Range, and near Bcirrow.
In early to mid-May, as many as 100,000 Red
Knots are estimated to stage on the Copper River Del-
ta (Isleib 1979) and from there apparently fly direct-
ly to breeding grounds in northwest Alaska and
possibly Siberia (Kessel and Gibson 1978). Recent
observations (Dau, unpublished; Gill and Handel, un-
published) indicate that between early and late May
the Yukon Delta supports a substantial segment of
the northbound population. Beginning the first week
of May in 1978 and 1979, large flocks of Red Knots
were seen approaching the coast from a south-south-
west direction. During mid-May in both years, several
thousands and perhaps a few tens of thousands of this
species fed daily on the exposed tide flats and flew in-
land to roost during high tides. Most were generally
gone from the area by early June (Gill and Handel,
unpublished). To the north in Norton Sound, the in-
tertidal zone is also used by knots each spring, but
not in the numbers found on the Yukon Delta (H.
Springer, personal communication). There are few
spring records of canutus from the Bering Sea islands
and none from the Alaska Peninsula (Kessel and
Gibson 1978).
In fall, knots show little preference for the inter-
tidal areas of Norton Sound (Shields and Peyton
1979; H. Springer, personal communication). Those
732 Marine birds
birds using the area move through in mid- August.
The bird is similarly scarce in north Bristol Bay and
along the Alaska Peninsula (Gill et al. 1977; Kessel
and Gibson 1978; M. Dick, unpublished). On the
Yukon Delta, however, adults begin using the mud-
flats in late June, and several thousand can be found
along the coast of the central delta by mid-July. Ju-
veniles do not appear until late July, but most remain
into early September. Red Knots fly daily between
feeding and roosting areas, just as they do in spring.
In fall, however, they often associate, especially at
roosts, with Bar-tailed Godwits (Gill and Handel, un-
published).
Sanderling (Calidris alba)
The Sanderling is not known to breed in the east-
em Bering Sea region (Kessel and Gibson 1978).
Away from the breeding grounds, this is a bird of
open coasts, usually sandy beaches and mudflats.
During spring migration, usually from mid- to late
May, Sanderlings are scarce in Norton Sound, but are
regularly found on the Yukon Delta, in upper Bristol
Bay, and along the Alaska Peninsula. They occur in
large numbers only at Izembek Lagoon (R.D. Jones,
FWS, personal communication). The birds that are
here have probably wintered in the Aleutians and are
moving east along the chain before dispersing to
northern breeding grounds.
In fall, Sanderlings move through Norton Sound in
August and early September, over the Yukon Delta
from early September through early October, and
along the Alaska Peninsula from mid- August through
October (Connors 1978; Gill et al. 1978; Gill and
Jorgensen 1979; Shields and Peyton 1979; Gill and
Handel, unpublished). There are few fall records of
Sanderlings from the Bering Sea islands (Kessel and
Gibson 1978). Sanderlings regularly winter in the
Aleutians and, depending on ice conditions, can be
found as far east as the central Alaska Peninsula
between November and March (Gill, unpublished).
Semipalmated Sandpiper (Calidris pusilla)
The Semipalmated Sandpiper is the most common
nesting "peep" of northwest Alaska. Its principal
breeding grounds are north of the Yukon Delta (Gab-
rielson and Lincoln 1959, Ashkenazie and Safriel
1979, Shields and Peyton 1979), but nesting does oc-
cur south to at least the mouth of the Kuskokwim
River (Gill and Handel, unpublished). This species ar-
rives on the breeding grounds in early to late May.
Over much of the Yukon Delta and portions of Nor-
ton Sound, the nesting habitat of pusilla is frequently
flooded by storm-driven tides in early spring and oc-
casionally during the nesting season.
The Semipalmated Sandpiper, unlike its congeners
the Dunlin and Western Sandpiper, makes little use of
littoral areas in this region after nesting (cf. Connors
1978, Connors et al. 1979, for Chukchi Sea coast).
Instead, pusilla generally remains on coastal wet
meadows and departs directly from these areas by
early August.
Western Sandpiper (Calidris mauri)
This species is an abundant nester over dwarf shrub
meadows throughout the eastern Bering Sea region,
including the Alaska Peninsula and Nunivak, St. Mat-
thew, and St. Lawrence islands (Gabrielson and Lin-
coln 1959, Holmes 1971a, Gill et al. 1977, Gill and
Jorgensen 1979). The Yukon Delta supports most of
the Alaska breeding population but substantial num-
bers breed as far north as the Seward Peninsula. West-
em Sandpipers arrive on the nesting grounds in mid-
May. Most have come from staging areas in the north
Gulf of Alaska (Connors 1978, Senner 1979).
After breeding, adult females are the first to move
to the coast. Throughout the region, this movement
occurs in early to mid-July (Holmes 1971a, 1972;
Gill and Jorgensen 1979; Shields and Peyton 1979;
Gill and Handel, unpubhshed). Adult males follow
soon, usually accompanying the first volant juveniles.
In Norton Sound, migration peaks in mid- to late
August. On the Yukon Delta, adults usually depart
by late July, but juveniles are present into early
September. Western Sandpipers exhibit similar
timing in their use of lagoons on the Alaska
Peninsula.
Rufous-necked Sandpiper (Calidris ruficollis)
This small Beringian sandpiper is known to nest in
western Alaska along the Seward Peninsula coast and
probably on St. Lawrence Island (Kessel and Gibson
1978). Reports of nesting birds are usually of sepa-
rate pairs. During spring and fall migration, ruficollis
is most frequently reported flocking with the very
similar Western Sandpiper.
Least Sandpiper (Calidris minutilla)
The Least Sandpiper nests commonly in coastal
wet and salt grass meadows along Bristol Bay, and
perhaps rarely on the Yukon Delta and in Norton
Sound (Gabrielson and Lincoln 1959; Shields and
Peyton 1979; H. Springer, personal communication).
Minutilla makes little use of littoral habitats in the re-
gion during spring migration; however, in fall, fair
numbers can be found throughout Bristol Bay in salt
grass meadows and occasionally on mudflats and
along flowing waters of major drainages (Gill and
Shorcbirds
733
Jorgensen 1979; M. Dick, unpublished; Gill, un-
published). Postbreeding adults are present from late
June through mid-July, and juveniles are present into
late August. Minutilla is probably a rare but regular
visitant to the Pribilof Islands (D. Gibson, personal
communication ).
Baird's Sandpiper (Calidris bairdii)
Baird's Sandpipers breed sparingly within the east-
em Bering Sea region from the Yukon Delta to Cape
Prince of Wales, including St. Lawrence Island (Ga-
brielson and Lincoln 1959). During migration they
occur throughout the region, usually as singles or in
small groups mixed with Western Sandpipers.
Pectoral Sandpiper (Calidris melanotos)
The principal nesting grounds of the Pectoral Sand-
piper occur north of the Yukon Delta, although this
species has been found nesting as far south as Bristol
Bay, and possibly breeds on St. Lawrence Island (Kes-
sel and Cade 1958, Fay and Cade 1959, Gabrielson
and Lincoln 1959, Pitelka 1959).
Pectoral Sandpipers seldom use littoral areas in
western Alaska in spring, flying instead directly to the
breeding grounds. In Norton Sound and areas farther
north, postbreeding birds use both littoral areas and
coastal wet meadows, peaking in numbers in late Au-
gust and early September (Connors 1978; Shields and
Peyton 1979; H. Springer, personal communication).
On the Yukon Delta comparatively few adults occur
along the coast or immediately inland (Gill and
Handel, unpublished; C. P. Dau, personal communica-
tion), suggesting that adults migrate in fall through
the interior. Juveniles, however, move to the vege-
tated supralittoral of the central delta, where they
occur by the thousands. They often associate with
juvenile American Golden Plovers and, to a lesser
extent, with Sharp-tailed Sandpipers (Gill and Han-
del, unpublished). In Bristol Bay and along the
Alaska Peninsula, melanotos is uncommon in fall (Gill
and Jorgensen 1979; Dick and Petersen, unpub-
lished). This species is a rare fall migrant on St. Law-
rence Island, but occurs regularly on the Pribilofs
(Preble and McAtee 1923, Fay and Cade 1959, Ga-
brielson and Lincoln 1959).
Sharp-tailed Sandpiper (Calidris acuminata)
This species, unlike the very similar Pectoral Sand-
piper, is not knowTi to nest in Alaska (Kessel and Gib-
son 1978). Instead, it occurs as a regular late summer
and fall visitor from breeding grounds along the coast-
al fringe of northeast Siberia (A. A. Kistchinski, The
Ringing Center, Moscow, personal communication).
Almost all fall records are of juveniles (Kessel and
Gibson 1978).
Within Alaska, most Sharp-taileds occur from Cape
Lisbume south, the majority congregating on the Yu-
kon Delta (Connors 1978; Schamel et al. 1979;
Shields and Peyton 1979; Gill and Handel, unpub-
lished). On the delta, beginning in late August, birds
appear in thousands and probably tens of thousands.
By mid-September, flocks of 100 birds are common
and occasionally flocks of 200 or more are seen.
Most of these are found over the extensive intertidal
of the central delta, including the littoral area of sev-
eral major rivers, where they most often associate
with juvenile Dunlin and juvenile American Golden
Plovers. Less commonly acuminata also use adjacent
wet meadows in association with Pectoral Sandpipers.
In Bristol Bay and on the Bering Sea islands, acu-
minata are seen less frequently and in smaller numbers
than to the north (Gill and Jorgensen 1979; M. Dick,
unpublished). Away from the eastern Bering Sea re-
gion, Sharp-taileds are reported regularly in fall in the
Aleutians (Byrd et al. 1974; Kessel and Gibson 1978;
G. V. Byrd, personal communication).
The number of Sharp-tailed Sandpipers occurring
on the Yukon Delta and the Seward Peninsula sug-
gests that western Alaska is part of a regular, age-
specific fall migration route for this species from Si-
beria. Birds from the delta and other areas probably
move across the eastern Bering Sea and along the
Aleutian and Komandorsky islands to wintering areas
in the southwest Pacific.
Rock Sandpiper (Calidris ptilocnemis)
The Rock Sandpiper is truly a shorebird of Be-
ringia. Three distinct races breed in the region, and a
fourth is known from the Commander Islands (see
Conover 1944, Gabrielson and Lincoln 1959). Many
birds winter in ice-free areas of the Bering Sea, al-
though most move to rocky coastlines in the Gulf of
Alaska and south to central California (Conover
1944, Gill 1979).
As early as mid-April, birds begin moving to the
breeding grounds, often while the nearshore intertidal
is still ice-fast. Here they congregate in large flocks
and forage extensively over the ice-free outer flats of
the Yukon Delta and Alaska Peninsula (Gill et al.
1977, 1978; Gill and Jorgensen 1979; Gill and Han-
del, unpublished). Birds continue to use the littoral
into early June. After breeding, usually by early
July, the first adults return to the tidal flats, followed
by juveniles in late July and early August. Flocks
gradually build until peak numbers are reached in
early September; once formed, flocks become rela-
tively sedentary and faithful to daily roosting and
734 Marine birds
feeding sites (Gill and Handel, unpublished). On the
Yukon Delta, roost sites are typically cut banks ad-
jacent to the intertidal (Gill and Handel, unpub-
lished), but rocky points and shores are more com-
monly used on the Bering Sea islands, Norton Sound,
and Alaska Peninsula (Gabrielson and Lincoln 1959).
Rock Sandpipers and Dunlin, which remain to
complete prebasic molt, are often the last shorebirds
to leave the northeastern Bering Sea region in fall,
with some birds remaining into November on several
Bering Sea islands.
Dunlin (Calidris alpina)
This species is the most abundant shorebird using
littoral areas along the west coast of Alaska, and the
principal breeding species throughout the coastal
fringe (Holmes 1971b, Gill and Jorgensen 1979). In
spring. Dunlin generally move directly to the breeding
grounds from staging areas on the Copper River Delta
(Isleib 1979, Senner 1979). However, on the Yukon
Delta during years of late snow-melt, birds congregate
and feed on adjacent ice-free intertidal until nesting
areas become available (Gill and Handel, unpub-
lished).
Postbreeding Dunlin move from nesting areas to
adjacent intertidal habitat beginning in mid-June,
where they undergo molt and usually remain to build
fat reserves for fall migration. Their use of the lit-
toral is among the most protracted of all shorebirds in
western Alaska, with both adults and juveniles re-
maining along the coast into early October (Gill and
Jorgensen 1979; Gill and Handel, unpublished; H.
Springer, personal communication). These birds ap-
pear to be highly faithful to roosting as well as feed-
ing areas, and often associate with Rock Sandpipers
at both sites. Individual roosts on the Yukon Delta
often comprise several thousands of birds and, occa-
sionally, several tens of thousands. Roosting sites are
generally adjacent to major feeding areas and are
often within the upper littoral zone.
Within western Alaska, there appear to be two or
possibly three distinct populations of Dunlin of the
race pacifica, whose nesting is restricted to the east-
ern Bering Sea region (MacLean and Holmes 1971,
Browning 1977, Gill and Jorgensen 1979). The two
major populations, in the Yukon Delta and Alaska
Peninsula, appear to winter in the Pacific northwest
and in central and northern California respectively
(Gill et al. 1978, Gill 1979). Dunlin from Norton
Sound appear to represent a third, albeit much small-
er, population, but little information exists on its
postbreeding movements or migration. The Yukon
Delta also hosts, beginning in August, several tens of
thousands of Dunlin of the race sakhalina, which
breeds in arctic Alaska and northeastern Siberia. In
1979, large flocks mainly of adults staged on the del-
ta before departing in late September or early Octo-
ber. Band recovery data and sightings of color-
marked birds from this population indicate that these
sakhalina winter in Japan and Korea (Gill and Handel,
unpublished).
Buff-breasted Sandpiper (Tryngites subruficollis)
This species is not knowm to nest within the east-
em Bering Sea region, nor does it occur regularly or
in numbers during migration (Kessel and Gibson
1978). There are, however, several records of its oc-
currence along coastal areas of western Alaska, in-
cluding the Pribilof Islands, Norton Sound, Yukon
Delta, and Alaska Peninsula (M. Petersen, unpub-
lished).
CONCLUSIONS
The shorebird resources of the eastern Bering Sea
region have global significance. For a third of the
species discussed, the area supports at some time the
main Alaska population and, in many instances, the
main North American population (Table 41-4). In
addition, major segments of populations of more
northern breeders move into the area during or pre-
paratory to fall migration. Combined, these popula-
tions represent several million birds. But while there
can be little question of the importance of the region
to these shorebird populations, we are less certain
why it is important and how this resource may be af-
fected by environmental changes.
Connors et al. (1979) indicate several biological
factors which partly determine the susceptibility of a
species to environmental disturbance in arctic Alaska.
These include distribution, habitat use, trophic rela-
tionships, and social systems and behavior. For the
most part the same issues are applicable to shorebird
populations in subarctic environs. The aspects of
these which must be addressed for each species in the
region are: What is the size of the population and are
there discrete subpopulations? What is the origin of
the population? How important is an area to the
welfare of a species? What are the food require-
ments of a species, both on the breeding grounds and
over littoral habitats? What food resources are avail-
able, and how do shorebirds respond to changes in
their availability? How mobile are populations which
depend on littoral areas after breeding? And by
what routes do birds migrate and where do they
winter?
Until these questions are answered, only a prelimi-
nary assessment can be made of the vulnerability of
these shorebirds to environmental disturbances. As
Shorebirds 735
TABLE 41-4
Shorebird species whose main Alaska (*) or North America (+) breeding or postbreeding populations
occur in the eastern Bering Sea region.
Breeding
+Black Turnstone (Arenaria melanocephala)
-i-Western Sandpiper (Calidris mauri)
+Rock Sandpiper (Calidris plilocnemis)
+Dunlin (Calidris alpina pacifica)
+Bristle-thighed Curlew (Numcnius tahitiensis)
Postbreeding
"American Golden Plover (Pluuialis dominica)
+ Bar-tai!ed Godwit (Limosa lapponica)
*Whimbrel (Numenius phaeopus)
*Red Knot (Calidris canutus)
' Sharp-tailed Sandpiper (Calidris acuminata)
* Breeds in northeastern Siberia.
Alaska each September.
A large but unknown segment of the annual juvenile population moves to coastal western
habitat use within the region changes dramatically
with the seasons, the susceptibility of a species also
changes. In winter and spring, very few species are
associated with littoral or supralittoral habitats.
During the breeding season, those species nesting in
numbers along the coastal fringe, particularly Black
Turnstones, Dunlin, and Semipalmated Sandpipers,
are most vulnerable, especially to changes in their
nesting habitat or food resources.
By far the greatest numbers of shorebirds are pres-
ent in the coastal areas of the region after breeding,
TABLE
from mid-July through late September. During this
period, many species become entirely dependent up-
on littoral and supralittoral habitats for premigratory
fattening and often through molt. For each of the
most common shorebirds of the region we present in
Table 41-5 an estimate of its relative susceptibility to
littoral zone disturbances. We have assigned each spe-
cies to a category based primarily on its dependence
upon littoral habitats, including the magnitude of this
use in relation to the total population, and the dura-
tion of dependence upon the habitat. For example,
41-5
Area
Relative susceptibility of common shorebirds to littoral zone disturbances.
High
Moderate
Low
Norton Sound
Yukon Delta
Bristol Bay
Bering Sea
islands
Northern Phalarope
Red Phalarope
Western Sandpiper
Dunlin
Bar-tailed Godwit
Black Turnstone
Western Sandpiper
Rock Sandpiper
Dunlin
Bar-tailed Godwit
Short-billed Dowitcher
Western Sandpiper
Rock Sandpiper
Dunlin
Northern Phalarope
Red Phalarope
Rock Sandpiper
American Golden Plover
Bar-tailed Godwit
Long-billed Dowitcher
Sanderling
Semipalmated Sandpiper
American Golden Plover
Black-bellied Plover
Whimbrel
Northern Phalarope
Red Knot
Sharp-tailed Sandpiper
Whimbrel
Ruddy Turnstone
Northern Phalarope
Red Phalarope
Long-billed Dowitcher
Sanderling
Ruddy Turnstone
Hudsonian Godwit
Whimbrel
Pectoral Sandpiper
Hudsonian Godwit
Bristle-thighed Curlew
Ruddy Turnstone
Long-billed Dowitcher
Pectoral Sandpiper
Greater Yellowlegs
Lesser Yellowlegs
Least Sandpiper
American Golden Plover
736 Marine birds
Dunlin and Western and Rock Sandpipers are consid-
ered highly susceptible because essentially the entire
population of adults and juveniles moves to littoral
areas and remains there until fall migration. We con-
sider species such as American Golden Plover and
Long- and Short -billed Dowitchers to be less suscep-
tible because large segments of the population remain
inland or move out of the region after breeding. Even
these, however, could become more susceptible if an
event such as an oil spill were coupled with a storm
surge in the early fall: the inland habitats could be-
come polluted— a situation easily realized over the
low-lying portions of the Yukon Delta and Norton
Sound. Until we better understand the dynamics of
shorebtrd populations in relation to the coastal habi-
tats, we will not be able to determine the extent of
the effects of environmental stress, whether it be the
result of man's activities or of natural causes.
Allen, A., and H. Kyllingstad
1949 The eggs and young of the Bristle-
thighed Curlew. Auk 66: 343-50.
Arneson, P. D.
1978 Identification, documentation and de-
lineation of coastal migratory bird
habitat in Alaska. In: Environmental
assessment of the Alaskan continental
shelf. NOAA/OCSEAP, Ann. Rep.
1:431-81.
Ashkenazie, S., and U. N. Safriel
1979 Breeding cycle and behavior of the
Semipalmated Sandpiper at Barrow,
Alaska. Auk 96:56-67.
ACKNOWLEDGMENTS
We thank G. V. Byrd, C. P. Dau, M. Dick, D.
Gibson, R. D. Jones, B. Kessel, M. Kirchhoff, A. A.
Kistchinski, M. Petersen, L. Peyton, G. Shields, and
H. Springer for sharing their unpublished observations
and data on shorebirds of the region. J. L. Lewds,
J. P. Myers, D. Gibson, and B. Kessel made helpful
comments on early versions of the manuscript. We
thank K. Boskofsky for typing the manuscript.
Much of the information we present in this paper was
obtained from field studies conducted on Clarence
Rhode National Wildlife Range, Yukon-Kuskokwdm
Delta, and supported by the U.S. Fish and Wildlife
Service. Our studies on the Alaska Peninsula were
supported in part by the U.S. Fish and Wildlife Ser-
vice and in part by the Bureau of Land Management
through interagency agreement with the National
Oceanic and Atmospheric Administration, managed
by the Outer Continental Shelf Environmental Assess-
ment Program.
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1948
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Waterfowl and Their Habitats
in the Eastern Bering Sea
James G. King
U.S. Fish and Wildlife Service
Juneau, Alaska
Christian P. Dau
Clarence Rhode National Wildlife Range
Bethel, Alaska
INTRODUCTION
To understand how birds use the Bering region, it
may help to visualize an hourglass, with the Pacific
Basin at one end, the vast tundras of Siberia, Canada,
and Alaska at the other, and the Bering Strait be-
tween. Birds funnel through this constriction twice
each year, in a mass movement which relates to geo-
logical history and evolution of the species as well as
to present climate and geography. We can only spec-
ulate as to the effect the Bering land bridge habitats,
occupying much of what is presently the eastern Be-
ring Sea and separated from the rest of the world by
great ice sheets, may have had on waterbird tradi-
tions, but certainly what we see now relates to those
phenomena. What we see is shorebirds and other
waterbirds moving north in spring. They linger and
stage in Bristol Bay in April, following the retreat of
the ice to the north. As leads open in the ice along
shore, some species follow them north while the
uplands are still locked in ice. Food is available in
these marine habitats; thus they afford a buffer in
times when the spring thaw is late on the nesting
grounds. When nest sites do become available, these
birds are ready to select territories often as the first
bare ground appears. Great numbers stop to nest on
the margin of the Bering Sea, but a large migration
passes through the strait to fan out into vast stretches
of American and Asian arctic coastal lands that were
covered by ice sheets in the recent past. The non-
breeding members of many waterfowl species often
remain in the marine habitat all summer, but may
move far north of their winter haunts. With the early
freeze of fall, birds forced from the wetlands again
take advantage of the availability of marine habitats
and move south leisurely through the Bering Strait to
Bristol Bay, building fat reserves that will carry them
to their wintering resorts far to the south. The great
bird migrations along the eastern Bering Sea were de-
scribed by Turner (1886), Nelson (1887), Brandt
(1943), Bailey (1948), Gabrielson and Lincoln (1959),
and others. Since 1959 more information has be-
come available, particularly through the Department
of Commerce environmental assessment of the Alaska
continental shelf and work by U.S. Fish and Wildlife
Service related to refuge management programs. But
it is a huge area and many of the details of this
wildlife drama are yet to be filled in.
The site of America's greatest goose nesting con-
centration is the Yukon Delta (Spencer et al. 1951).
Clarence Rhode National Wildlife Range was estab-
lished here in 1960 and since then biologists have
been in residence. The Yukon-Kuskokwim Delta
encompasses some 68,120 km^ , about 14 percent of
which is covered by vascular plant communities that
are affected by periodic tidal floodings. This region is
the terminus of the migrations of a large portion of
the arctic nesting waterfowl of the Pacific Basin and
adjacent continents.
Information on some Bering Sea habitats has been
presented by the Arctic Environmental Information
and Data Center (AEIDC) (1974), Sears and
Zimmerman (1977), and Arneson (in press), but
no one has previously tried to determine the full ex-
tent of important marine areas used by waterfowl.
Our scrutiny of the best available maps discloses that
these habitats consist of 98,446 km" of shallow
marine waters, 6,018 km' in 97 saltwater lagoons and
27 river mouths, and 16,157 km^ of intertidal habitat
(Table 42-1). The shallow marine waters are particu-
739
740 Marine birds
larly valuable to diving ducks for much of the year.
The lagoons are heavily used for feeding by geese and
ducks during migration periods. More than 75
percent of the intertidal habitat is on the Yukon
Delta, where low tides prevailing in May and June
allow this habitat to accommodate densities of up to
400 waterfowl nests per km^ . In general, we cal-
culate that of 109.2 million waterfowl in the average
fall population for North America, 11.6 million or
about 11 percent utilize Bering Sea habitats. The dis-
tributional information presented here reflects a
dearth of specific data, but we are beginning to learn
the general pattern of bird movements within the
Bering Sea area. Our species accounts mainly deal
with the Yukon Delta, for that is where the most ex-
tensive studies of waterfowl have been done.
In sum, our knowledge of waterfowl biology in this
huge and remote area is largely superficial. This is un-
fortunate in a region thought to contain a huge oil re-
serve (Bartonek et al. 1971).
METHODS
In order to develop a quantitative picture or profile
of the gross habitat features of the eastern Bering Sea
that are exploited by waterfowl, we turned to exist-
ing maps of the area. An electronic digitizer (Numon-
ics Corp. Model 1224) was used to measure shorelines
and calculate the size of various areas. These data are
presented in Table 42-1.
For the area of salt water less than 18 m deep,
National Ocean Survey Navigation Chart 9302
of the eastern Bering Sea was used. All other calcula-
tions are from U.S. Geological Survey maps. When
available, maps of the scale 1:63,360 (1 inch = 1 mile)
were used, but for the tip of the Alaska Peninsula and
the island habitats except Nunivak, maps of the scale
1 :250,000 (1 inch = 4 miles) were used. All U.S. Geo-
logical Survey maps are from photographs made in
the period 1947 to 1963. Some changes have oc-
curred along the coast since then, but not enough to
significantly affect our figures. Generally losses are
balanced by gains as coastlines and river mouths
change.
The results obtained by measuring maps are re-
lated to the scale of the maps. We have found that
measuring shorelines on a 1:63,000 scale produces
20-30 percent higher figures than using the 1 : 2 50, 000
scale. The best figure could probably be achieved
only by surveyors chaining off the land in the classic
fashion. There is no question that surveyors would
find our figures conservative, but they are accurate
enough to indicate the vastness of the habitat avail-
able.
Other people calculating figures from these maps as
we did or usmg other equipment would doubtless
have produced slightly different figures, since deci-
sions are necessary on each map regarding how and
what to record. We believe that the gross figures are a
valid though conservative profile of the extent of ma-
rine habitats of the eastern Bering Sea.
The size and importance of the waterfowl re-
sources of the eastern Bering Sea are given in Table
42-2. We estimate the numbers of each species, using
eastern Bering habitats compared with the total conti-
nental population.
Continental population figures are derived from
Bellrose (1976) and management documents of the
U.S. Fish and Wildlife Service. These means are de-
rived from annual surveys since 1950. Swan and goose
populations in Bellrose's book are from winter inven-
tory figures and ducks are from spring breeding pair
surveys. To get fall populations we have adjusted his
spring figures for annual production and winter fig-
ures for fall migration and hunting mortality. We have
settled on the following correction factors after re-
view of data in Bellrose (1976) :
swan breeding population + 20 percent = fall popula-
tion,
goose breeding population + 40 percent = fall popula-
tion,
goose winter population + 20 percent = fall popula-
tion,
diving duck breeding population + 80 percent = fall
population,
dabbling duck breeding population + 100 percent =
fall population.
Table 42-2 shows averages. Peak populations for all
species are substantially higher and some dabblers
(Anatini) can achieve double the mean population
presented here.
BERING SEA HABITATS
We have separated Bering Sea habitats into four
natural geographical divisions: Bristol Bay from Cape
Serichef on western Unimak Island to Cape Newen-
ham; the Yukon Delta from Cape Newenham to Stu-
art Island; Norton Sound from Stuart Island to Bering
Strait; and four large island areas: St. Lawrence,
Nunivak, St. Matthew, and the Pribilofs (see Fig.
42-1). Cape Prince of Wales in Bering Strait is about
1,287 km north of Cape Serichef with 10,881 km of
beach line between.
Bristol Bay lies generally within the north temper-
ate climatic region. Uplands are unfrozen much of
the year and the sea remains essentially ice-free all
winter. Upland lakes may be frozen from late No-
vember through February on the south side of Bristol
TABLE 42-1
Bering Sea habitats for waterfowl and siiorebirds
Area of
salt water
Number of
Region and
less than
Length of
large tidal
Area of
Area of
Area of
number of
Unit of
10 fathoms'
beach
Number of
Area of
river
river
unvegetated
vegetated
Number of
Number of
maps scaled
measure
(18.29 m)
line^
lagoons^
lagoons
mouths'*
mouths
intertidal^
intertidal*
rivers'
streams*
Bristol Bay
Serichef to
Eng.^
7,293
2,022
31
797
3
61
708
325
56
749
Newenham
Met.''
1,889,689
3,262
206,381
15,943
183,450
84,211
61 maps
Yukon Delta
Newenham to
Eng.
18,010
2,538
13
398
22
548
1,201
3,571
171
2,097
Stuart I.
Met.
4,666,571
4,094
103,066
141,873
311,191
925,282
68 maps
Norton Sound
Stuart I.
Eng.
9,326
1,006
16
340
2
8
106
171
49
386
Wales
Met.
2,416,460
1,623
88,105
2,174
27,466
44,308
39 maps
Sea Islands
St. Lawrence
Nunivak
Eng.
2,946
1,179
37
145
48
37
40
399
St. Matthew
Met.
763,338
1,902
37,579
12,437
9,587
Pribilof
16 maps
TOTAL
Eng.
37,575
6,745
97
1,680
27
617
2,063
4,104
316
3,631
184 maps
Met.
9,736,058
10,881
435,131
159,990
534,544
1,063,388
^Area in square miles; length in statute miles
''Area in hectares; length in kilometers.
' Area of salt water. This has been calculated on a rather large-scale map (1 cm = 15.2 km), but gross area figures are less affected
by map scale than lineal measure of complex shorelines.
^Length of beach line. The cartographers used the obvious vegetation line to delineate the shoreline on their maps. They show
some intertidal lands below this line. Our measurement is an attempt to show the extent of salt water/land interface; thus, it
includes the shoreline within lagoons and river mouths. Surveyors actually measuring each slough or creek mouth would get a
much larger figure.
^ Number of lagoons. We measured 97 lagoons, some of which appear on portions of up to three maps. Many tiny lagoons are not
on the maps, although birds use them. Lagoons are protected from the open sea by islands, barrier beaches, or points. All lagoons
are estuaries, but some have a much greater influx of fresh water than others.
^ Large tidal river mouths. These are rivers shown on maps with two banks, so that the area can be measured. We attempted to
scale the area subject to salt water intrusion during high tidal surges. The multiple mouths of the Yukon River known locally as
passes constitute most of this category. Since there is some difficulty distinguishing between rivers and tidal sloughs, some arbi-
trary decisions had to be made.
^ Unvegetated intertidal. These areas are shown as mud flats on the maps. The extent of mud flats shown depends on the level of
the tide at the time the aerial photos were taken. In many areas the authors know that low tide exposure of mud is more exten-
sive than shown on the maps, and our figures include such areas. The term unvegetated intertidal is convenient but not entirely
correct. Various nonvascular plants can be found in these areas and in some places extensive growths of eel grass (Zostera sp.).
^Vegetated intertidal. This area is essentially the terrain between the outer edge of vascular plant growth (not including Zos/eraJ
and the line of driftwood cast up by high tides. It is normally a wet sedge/grass meadow ('Carcx/Gramineae sp.). Maps do not
show the driftwood line but they do show elevations below 7.62 m and in many places the 7.6 m contour. Years of ground and
aerial survey experience enabled us to draw in the approximate drift line.
^Number of rivers. This refers to streams shown by two lines and/or named as rivers on the map that are not large enough to be
scaled.
^ Number of streams. These show on maps as single blue lines. We did not try to distinguish between bona fide streams and tidal
drainage gutters, but included whatever shows on the maps.
741
TABLE 42-2
North American waterfowl populations in relation to the use of Bering Sea habitats
(*Nesting range includes Bering intertidal zone)
Species
Total North American
fall population
Number that use
Bering habitats
%
Whistling Swan, Cygnus columbianus
Total swan
White-fronted Goose, Anser albifrons
Lesser snow G., Anser caerulescens caerulescens
Emperor G., Philacte canagica
Cackling Canada G.,Branta canadensis minima
Taverner's Canada G., B.C. tavemeri
Aleutian Canada G.,B.c. leucopareia
Black Brant, Branta bernicla nigricans
Total geese
American Wigeon, Anas americana
Gadwall, Anas strepera
Green-winged Teal, Anas crecca
Mallard , Anas platyrhynchos
Pintail, Anas acuta
Northern Shoveler, Anas clypeata
Total dabblers
Canvashack, Ay thy a valisineria
Greater Scaup, Ay thya marila
Lesser Scaup, Ay thy a af finis
Common Eider, Soma fena mollissima
King Eider, Somateria spectabilis
Spectacled Eider, Somateria fischeri
Steller's Eider, Polysticta stelleri
Harlequin Duck, Histrionicus histrionicus
Oldsquaw, Clangula hyemalis
Black Scoter, Melanitta nigra
Surf Scoter, Melanitta perspicillata
White-winged Scoter, Melanitta fusca
Bufflehead, 5ucep/za/a albeola
Barrow's Go\deneye , Bucephala islandica
Common Goldeneye, Bucephala clangula
Red-breasted Merganser, Mergus serrator
Total divers
Total waterfowl
(Species occurring in Bering Sea)
Whistling Ducks, Dendrocygnini
Trumpeter Swan, Cygnus buccinator
Mute Swan, Cygnus olor
Geese, Anserini
Dabblers, Anatini and Cairinini
Divers, Mergini and Oxyurini
Subtotal
(Species not using Bering Sea)
Total North America
160,000
30,000*
19
160,000
30,000
19
240,000
67,000*
28
1,532,000
150,000
10
150,000
150,000*
100
150,000
150,000*
100
100,000
50,000*
50
1,700
1,700
100
150,000
150,000*
100
2,323,700
718,700
31
6,278,000
200,000*
3
3,284,000
2,400*
0.1
4,384,000
20,000*
0.5
20,714,000
20,000*
0.1
12,386,000
1,222,000*
10
3,770,000
20,000*
0.5
50,816,000
1,484,400
3
1,008,000
Trace
—
1,350,000
338,000*
25
11,070,000
12,000
0.1
2,000,000
750,000*
38
1,980,000
1,790,000
90
250,000
250,000*
100
400,000
400,000*
100
3,000,000
1,000,000
33
7,200,000
3,600,000*
50
977,000
489,000*
50
463,000
116,000
25
1,215,000
401,000
33
1,341,000
61,000
5
270,000
Trace
—
2,250,000
110,000
5
500,000
20,000*
4
35,274,000
9,337,000
27
88,573,700
11,570,100
14
16,000
6,000
4,000
3,055,000
13,023,000
4,568,000
20,672,000
109,245,700
11,570,100
11
742
Waterfowl and their habitats 743
Bay and on the north side from late October to April.
Extensive lagoons along the shore include some of the
biologically richest marine habitats in the world
(McRoy 1968, Kelley and Hood 1973). The head of
the bay is shallow with a sandy bottom that is exten-
sively exposed by the high diurnal tidal fluctuations.
North of Cape Newenham is the huge Yukon
Delta, created by a drainage pattern and sedimentary
basin extending back to pre-Cambrian times (Williams
1958). The Kuskokwim River, Alaska's second larg-
est, is now separate from the Yukon, but they have
been joined in the past; thus, since the terms Yukon
Delta and Kuskokwim Delta are actually synonymous,
we call this geographic feature simply the Yukon Del-
ta. The land gradient here is very low and tidal ranges
high, approximately 3 m at the coast, creating the
greatest expanse of intertidal habitat anywhere on the
Pacific side of the Americas. U.S. Weather Bureau rec-
ords show a normal series of low-pressure areas
(storms) passing west to east over the Bering Sea dur-
ing long periods of every year. They are least intense
in spring and most intense in fall. High onshore winds
accompanying these storms send Bering Sea waters
far inland at regular intervals. Mud and silt impaction
of vegetation in coastal meadows and variable effects
of ice scouring can result from these storm-surge in-
trusions. The climate of the Yukon Delta is arctic.
Permafrost is characteristic on land and has been mea-
sured to depths of 122 m at the head of Kuskokwim
Bay. Lakes on the upland and the vegetated inter-
tidal zone are frozen from early October to late
May, and the sea is frozen from November to April.
Norton Sound is a vast shallow area with extensive
lagoons and tidal marshes along the shore. The boreal
forest reaches the edge of Bering Sea on the east side
of Norton Sound, while the climate is so extreme at
the west end that the upland is largely devoid of vege-
tation. No waterfowl studies have been done in this
area.
The four island groups have shallow nearshore
feeding areas, lagoons, and intertidal habitats similar
to those found on the adjacent mainland at the same
latitude.
The Bering Sea habitats can be subdivided further
into four types:
Nearshore waters
The whole Bering Sea is traversed by waterfowl,
but they tend to concentrate for feeding in the shal-
lower waters. Diving ducks which feed on bottom or-
ganisms are particularly dependent on this habitat. It
is used the year round except when ice cover ren-
ders it unavailable. Shallow marine waters provide
both a water corridor and staging area for birds wait-
ing for nesting habitat on shore to thaw and an easy
escape from the early fall freeze of upland fresh
water.
Lagoons
Lagoons everywhere are popular with birds because
they provide shelter from the power of the open sea
and contain a rich biota. The lagoons of the eastern
Bering Sea are particularly extensive and rich and are
well placed along most of the shore to provide accom-
modation for transients (Fig. 42-1). Fifteen of these
lagoons contain abundant stands of eelgrass. Since
Izembek Lagoon has the largest and richest growth of
eelgrass in the world, it is not surprising that it is a
mecca for northern waterfowl and particularly Black
Brant (McRoy 1968). Although lagoons throughout
eastern Bering habitats show many similarities in size,
depth, and associated vegetative communities, there
are dramatic seasonal differences in environmental
conditions. Ice dominates most lagoons and bays
along the middle and northern Bering Sea coastline.
Moreover, south-facing lagoons in Norton Sound and
Bristol Bay are affected by the fury of Bering storms
more than the north-facing lagoons of the Alaska Pen-
insula. Wave action, ice scouring, and salinity appear
to restrict the extent of vegetative communities and
may have dramatic effects on the benthic fauna.
Unvegetated intertidal
In Bristol Bay the unvegetated intertidal zone is
largely unstable sand, particularly along the steep
beaches and at the head of the bay. But some unvege-
tated intertidal occurs in the lagoons, where there are
extensive mud flats and silt. The silty mud is richer
than the sand in the invertebrate life upon which
many species of birds depend. The outer Yukon
Delta is mostly silt and mud, and provides the most
extensive block of this kind of habitat in the Amer-
icas.
Vegetated intertidal
This habitat is characterized by low, wet meadows,
covered by sedge (primarily Carex sp.) and grass, usual-
ly within 40 km of the beach; driftwood lines adja-
cent to areas of upland tundra mark its border. Some
of this habitat is inundated nearly every day, some on
several days of every month, and some only on sev-
eral days of the entire year. Violent storm surges oc-
curring every year during the fall and winter and oc-
casional spring storms push Bering Sea waters far be-
yond their normal range, particularly on the Yukon
Delta. This periodic intrusion from the sea affects
land forms, water characteristics, the distribution of
plants, and the general configuration of the habitat.
744 Marine birds
170° 175°
180° 175°
170°
165°
160°
155°
150°
65°
liiii
100
200 km
' i 1 1
1 1 1 1
1 1 . m:
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/
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miles
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.i£„.!......,..,;.;.;:;:i:,;:;;:::;il!|
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33.
34
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23
22
62°
w
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.V
y
62°
EASTERN BERING
SEA-
MAJOR LAGOONS AND
RIVERS
19 \
/^
^-'"^^
MAJOR LAGOONS
g
c
11
BRISTOL BAY
HA
NORTON SOUND
HA
t
ill
1 BECHKVIN BAY
24,128
22. ST. MICHAEL BAYS
2,003
41 ♦
.-..♦. 1& ^
.■5:!:iW
2 IZEMBEK BAY
34,410
23
UNALAKLEET LAG. ■■:■■•■■
907
59°
3 NELSON LAG.
1. MUD BAY
14,080
6,315
24
25
BEESON SLOUGH
MALIKEIK BAY
661
700
■43*42
r
59°
5. HERENDEEN BAY
19,060
2G
KWINIUK INLET
1,355
17
b
6. PORT MOLLER
44,570
27
GOLOVNIN LAG.
14,254
c
7. SEAL ISLAND LAG.
5,050
28
SAFETY SOUND
6,118
*W
S:%;>:^:^
8. PORTHEIDEN
20,395
29
TISUK LAG.
998
^s\,
-^--«
;::§xSS^
9. CINDER RIV. LAG.
3,780
30
GRANTLEY HARBOR
7,372
;»*
iiir
10. UGASHIK BAY
12,461
31
PORT CLARENCE
48,612
*
.«
I-:-::-:-:-:; ■
:■:■:■:■ '
11. EGEGIK BAY
7,405
32
BREVING LAG.
3.716
13
:$!:■■
12. KULUKAK BAY
7,499
'-■>.
13. NANVAK BAY
1,334
SEA ISLANDS
.**
YUKON DELTA
33. AGHNAGHAK LAG.
34. NIYRAKPAK LAG.
1.244
3.773
•9
14. CH.AGV.AN BAY
3.322
35. TOMNAME L.AG.
912
15. GOODNEWS BAY
13.399
36. SEEPANPAK LAG.
2.446
.9
16. NANVAKFAK LAG.
1,480
37. KILOKNAK LAG.
1.368
,7
56°
17. CARTER BAY
4,558
38. MAKNIK LAG.
2,9fl5
_ _o
18. KANGIRLVAR BAY
8,372
39. SEKINAK LAG.
4.685
^
56
19. HOOPER BAY
17.153
40. KOOZATA LAG.
11,484
•■•■•
.&
20. KOKECHIKBAY
15.720
41. MEKORYUK LAG.
788 ■•■■•
3 .6
21 SCAMMON BAY
37,281
42. DUCHIKTHLUK BAY
3,003
43. BANGOOKBIT LAG.
601
***-s
RIVERS
HA
2
a. NAKNEK
2,000
1^
b. KVICIIAK
4,231
c. NUSII.\GAK
9,711
d. KUSKOKWIM
61,702
-^
1-. KOLAVINARAK
6,841
r. NINGLICK
17,275
B. AZUN
6,250
53°
h. MANOKINAK
3,915
53°
1. APHREWN
3,835
__
J. MOUTH OF YUKON
33,662
k KOYUK
1,205
1 KWTK
969
180°
175"
170°
165°
160°
Figure 42-1. Major lagoons and rivers of the eastern Bering Sea.
To varying extents, all these factors affect the distri-
bution of birds. Because the land is seldom inunda-
ted by storm surges in June, it is extensively used by
nesting birds, and some species depend on it almost
exclusively. Vegetative communities within this zone
are described in some detail by Mickelson (1975),
Eisenhower and Kirkpatrick (1977), and Jackson
(1973).
SEASONAL ACTIVITIES OF WATERFOWL
The spring migration of birds over the coastal habi-
tats of the Bering Sea is the most impressive occur-
rence of the annual cycle, and waterfowl are the most
spectacular element of this movement. In early April
waterfowl begin to congregate at the southern end of
the Alaska Peninsula. Black Brant, Emperor Geese,
Pintails, and King Eiders and other diving ducks
appear in large numbers at Izembek Bay and adjacent
lagoons. As spring freshets and high tides clear the ice
from lagoons farther north, the birds move up,
crossing the head of Bristol Bay in mid- to late April
and continuing north to the Yukon Delta nesting
habitat and beyond. This migration has been de-
scribed by Nelson (1887), Dufresne (1924), Murie
(1924), Conover (1926), Jaques (1930), Gillham
Waterfowl and their habitats 745
(1941), Bailey (1943, 1948), Brandt (1943), and Dau
(1972,1974).
Sea ducks, primarily eiders and Oldsquaw, may ap-
pear in large numbers in offshore waters of the Yu-
kon Delta as early as mid-April and are abundant in
this area along with other species through mid-May.
Whistling Swans, White-fronted Geese, Taverner's and
Cackling Canada Geese, and Pintails are among the
first migrants to arrive on the Yukon Delta in the
spring. The peak influx of those species is normally
in the first week of May.
Although some nesting occurs in Bristol Bay habi-
tats, that region is far more important for migrational
staging. The spectacular nesting concentrations begin
north of Cape Newenham, peak on the Yukon Delta,
and decline north of Bering Strait. Nesting begins on
the delta in late May. Nonbreeding brant and diving
ducks continue passing north along the coast to the
Bering Strait through early June.
Localized movements of nesting birds dominate
the scene in June and early July on the delta. The
peak of the hatch generally coincides with the longest
days of the year.
Whistling Swans and geese, because of their large
size, are the most conspicuous of the waterfowl
species nesting in the vegetated intertidal zone of
eastern Bering Sea. Although the distribution of
nesting waterfowl in coastal habitats is affected by a
wide array of climatic and topographic factors, in all
the species we have investigated the highest densities
occur in the vegetated intertidal zone. In some areas
close to the beach, waterfowl densities may approach
400 nests per km^ , including swans, brant, other
geese, and ducks.
Movements of most waterfowl in July are mini-
mized in preparation for the molt. Emperor Geese
that did not nest or failed to produce are an excep-
tion to this pattern in that they maintain a well-
established molt migration to St. Lawrence Island
(Jones 1972). A similar movement of Emperor Geese
may take place from areas in the Soviet Arctic
(Kistchinski 1973). By mid-August, nonbreeding
geese molting on the Yukon Delta have regained
flight, and by the end of the month they are joined
by an influx from the north. Successful nesting
adults and their young can fly by the end of August,
and localized movements within or between preferred
nesting areas increase until the fall exodus in October.
Inland and coastal routes over the Yukon Delta are
used by fall -migrating geese. Lesser Snow Geese ar-
riving in mid- to late September from Wrangel Island
in the Soviet Arctic rest on St. Lawrence Island and
then move to areas within the unvegetated and vege-
tated intertidal, south of the mouth of the Yukon
River. These birds appear to move rapidly to upland
habitats primarily south and east of Nelson Island,
where they may stay for a month building fat re-
serves. A bifurcated migration occurs from this area:
most of the birds pass south into Bristol Bay and
others move east through mountain passes and into
the north coast of the Gulf of Alaska.
Cackling and Taverner's Canada Geese follow a
predominantly coastal route during fall migration;
major staging concentrations appear on Nunivak Is-
land and the north side of the Alaska Peninsula. Black
Brant and Emperor Geese are also tied closely to Be-
ring habitats during fall migration, with centers of
concentration in or adjacent to lagoons and bays
from Nunivak Island south to Izembek Bay and False
Pass.
Both diving and surface-feeding ducks are far more
dispersed during the fall migration than during the
spring, with the exception of scoters and Pintails.
Eiders, largely King Eiders, bring up the rear of fall
migration past the Yukon Delta in November.
Our information is most deficient during winter
(McRoy et al. 1971, h-ving et al. 1970, Dau and
Kistchinski 1977, Divoky 1979). Limited amounts of
open-water habitat are available even during the
harshest of vdnters, usually south of major islands.
Open leads and polynyas, often found near shore, can
supply important wdntering habitats for some birds.
In mild winters the amount of available open-water
habitat is extensive as far north as Bering Strait.
Numerous areas of suitable depth for bottom-foraging
birds are available, particularly in Norton Sound. It is
believed that large numbers of sea ducks, especially
eiders, may use these habitats in winter.
SPECIES ACCOUNTS
Table 42-2 lists 30 waterfowl species and sub-
species regularly occurring in the eastern Bering Sea.
We include here short species accounts of the 19
waterfowl taxa whose total populations could be af-
fected by adverse conditions in the Bering Sea. Other
species do occur in this area, but since their numbers
are very low, their current population status does not
depend on what happens in the Bering Sea. Much of
the information presented here is from the unpub-
lished observations, notes, and reports of the authors.
Whistling Swan (Cygnus columbianus)
The Whistling Swan is the most conspicuous and
one of the most widely distributed nesting species
in coastal areas of the eastern Bering Sea. The species
is common during spring and fall migration. Although
Whistling Swans nest throughout the lowlands adja-
cent to the Bering Sea, the largest concentration.
746 Marine birds
approximately 0.4 nests per km^ , occurs in the vege-
tated intertidal area of the Yukon Delta. Maximum
densities encountered in this area approach one nest
per km^ . Nonbreeding flocks of up to a thousand or
more birds also use the vegetated intertidal zone. Per-
haps 60 percent of the Pacific Flyway swans depend
on this intertidal habitat for most of the summer.
The modal arrival date for Whistling Sv^^ans on the
Yukon Delta is 1 May, with peak influx usually oc-
curring from 30 April to 2 May. They use a variety
of habitats for nesting but seem to prefer areas char-
acterized by mixed upland tundra and wet sedge/grass
meadow. The highest nesting densities seem to occur
in this kind of habitat; fewer nests appear in open,
wet meadows.
The onset of nesting, nesting distribution, and pro-
duction are dictated to a large extent by spring cli-
mate and its effects on snow melt. Whistling Swans
begin gathering in early September and departing by
mid-month, but some linger on until freeze-up in
early October.
Cackling Canada Goose (Branta canadensis minima)
The Cackling Canada Goose is one of the most
numerous goose species occupying the vegetated inter-
tidal zone of the eastern Bering Sea. The entire world
population nests in this eirea, with the vast majority
occurring on the Yukon Delta. The modal arrival date
of this species in high density areas of the delta is 3
May with peak influx normally from 5 to 8 May. An
early spring migrant, the Cackling Canada Goose pre-
fers low, wet meadows dominated by sedge and grass
species; it occupies these meadows from arrival
through the pre-fledging period. Small to medium-
sized (x = 0.5 ha; range up to = 3.5 ha), irregularly
shaped, shallow (< 0.75 m) ponds dominate these
meadow areas. Most ponds contain many of the small
islands preferred as nesting sites.
Nesting densities of Cackling Canada Geese can ex-
ceed 40 nests per km^ in the vegetated intertidal
(Mickelson 1973, 1975; Dau and Mickelson 1979).
During the post-fledging period before fall departure,
this species spends comparable amounts of time
foraging on crowberries (Empetrum nigrum) in
uplands and on vegetation and invertebrates in wet
meadows. Storm tides and ice action can adversely
affect this species by altering the habitat during fall
or winter. Storm surges also occasionally destroy
eggs and young during spring and summer. Large
numbers of Cackling Canada Geese work their way
south along the coast in September to Ugashik Bay in
Bristol Bay, where they remain through early Octo-
ber. At Ugashik they feed in intertidal meadows and
are the target of fairly intensive sport hunting.
Taverner's Canada Goose (Branta canadensis tauerneri)
The taverneri subspecies of the Canada Goose, like
minima, is an early spring migrant to habitats of the
eastern Bering Sea. It is a dispersed nesting species in
western and northern Alaska with the greatest abun-
dance in the Yukon Delta. It is estimated that fewer
than 0.4 nests per km^ occur in the vegetated inter-
tidal zone of this area. Although this species seems to
prefer upland-dominated areas inland of this zone for
nesting, low densities are found throughout its range.
During spring and fall, migration concentrations of
Taverner's Canada Geese occur along the Kuskokwim
and Yukon rivers, as determined from spring harvest
data (Klein 1966; unpublished data, Clarence Rhode
National Wildlife Range). In addition, fall concentra-
tions aire found on Nunivak Island, where lagoons and
bays, as well as uplands, are extensively used. Similar
usage patterns exist on coastal habitats from Kusko-
kwim Bay to the Alaska Peninsula, where several large
concentrations occur. At Izembek Lagoon some
50,000 feed on the uplands and rest on the lagoon for
some weeks before their flight south in early Novem-
ber.
White-fronted Goose (Anser albifrons)
Within habitats of the eastern Bering Sea, the
White-fronted Goose occurs as an abundant nester
only on the Yukon Delta. Approximately 95 per-
cent of the Pacific Flyway population uses this
area; an estimated 60-80 percent nest on the delta
within the vegetated intertidal zone.
The modal arrival date for White-fronted Geese on
the delta is 2 May, with the peak influx of migrants
usually arriving from 1 to 3 May. White-fronted Geese
appear to follow inland migration routes in spring
and fall; concentrations occur in both periods along
the Kuskokvdm and Yukon rivers and associated
drainages.
The White-fronted Goose prefers nesting on ele-
vated, comparatively dry slough and river borders and
in interface zones between upland tundra and wet
sedge/grass meadows. Nesting densities up to 3 nests
per km^ have been found in these areas. Slough and
river-border nests are highly susceptible to destruc-
tion by storm-tide flooding. However, high, relatively
stable productivity suggests that the nesting distribu-
tion of this species is dispersed within the vegetated
intertidal zone and largely in the periphery, where
only the most extensive floods damage production.
After the hatching period, adult White-fronted
Geese and their young appear to prefer upland areas,
mostly outside the vegetated intertidal zone. They
often remain near tidal rivers and sloughs, which
molting and brood flocks enter when disturbed. When
Waterfowl and their habitats 747
the young have fledged and the adults have regained
flight capabihties in mid- to late August, a gradual
eastward movement of family groups, sometimes in
moderate-sized flocks, occurs. Few White-fronted
Geese remain in the vegetated intertidal zone by mid-
September.
Black Brant (Branta bernicla nigricans)
An estimated 30-50 percent of the world popu-
lation of Black Brant nests in the vegetated intertidal
zone of the eastern Bering Sea. All of these occur on
the Yukon Delta, where nesting densities exceeding
1,500 nests per km" have been recorded. The average
nesting density for area within the vegetated
intertidal zone and less than 3 km from the beach is
230 nests per km' . In the inland portions of the
vegetated intertidal zone, small scattered colonies of
Black Brant exist, usually with fewer than 30 pairs.
The distribution and abundance of these colonies
within the zone are unknown.
The modal arrival date for Black Brant on the Yu-
kon Delta is 11 May; peak influx usually occurs from
15 to 18 May. Migrants passing through to more
northern areas continue through June. Migrants pro-
ceeding north of the Yukon use lagoons on the north
side of Norton Sound extensively.
The preferred habitats of Black Brant during the
nesting season are of two types: meadows dominated
by sedge and grass with numerous small, shallow
ponds have supported high densities in most years;
slightly elevated mud flats broken by pads of sedges
and tidal sloughs lined with beach rye (Elymus sp.)
have supported high densities in climatically early
years. The latter area exhibits only sporadic produc-
tivity even in early years because of its susceptibility
to inundation by storm tides. Rates of snow and ice
melt dictate the time nesting habitat is available.
Inland colonies of Black Brant are found in ponded,
wet meadow areas and appear to have routinely low
productivity due to competition for preferred nest
sites with other goose species and high rates of preda-
tion. Both these factors may be functions of the low
numbers and wide dispersion.
Brant leave the delta in late August and return to
marine habitats where eelgrass is present in lagoons.
By October, the entire world population is concen-
trated at Izembek and three nearby lagoons, where
they remain until their avalanche migration in early
November (Bellrose 1976, Palmer 1976).
Emperor Goose (Philacte canagica)
The Emperor Goose is almost exclusively a Bering
Sea bird, migrating along the coast from wintering
places in the Aleutian Islands to its principal nesting
place on the Yukon Delta. A very small population
nests in Siberia. They are said to have been known
as the "beach goose" to the Aleut people, as opposed
to the "sea goose" (Black Brant) and the "land goose"
(Canada Goose).
The Emperor Goose occupies all neairshore and
coastal eastern Bering Sea habitats at various times of
the year and is seldom far from tidewater. Nesting
occurs from just north of Cape Newenham to the
Seward Peninsula. An estimated 90 percent of the
world population of Emperor Geese nests on the
Yukon Delta, over 90 percent of these probably in
the vegetated intertidal zone.
The modal arrival date for Emperior Geese on the
Yukon Delta is 12 May; the peak influx is usually
from 14 to 16 May.
Emperor Geese prefer wet meadows for nesting
and compete for insular and shoreline nesting sites
with Cackling Canada Geese and Spectacled Eiders.
The large number of available nest sites, relatively
small territory sizes, and differential timing of nest-
site selection tend to limit competition.
Nesting densities up to 27 nests per km' have been
recorded at one study location within the vegetated
intertidal zone (Eisenhower and Kirkpatrick 1977).
Densities of approximately 4 nests per km" recorded
at other sites within this zone may be more represen-
tative of the total area.
Although Emperor Geese compete wdth other
waterfowl species for nesting sites, they do exhibit
the ability to nest successfully in less preferred habi-
tat. Dispersed nesting may be a function of compe-
tition for nest sites or the timing of nest initiation,
which is usually slightly later than for other species.
Lesser Snow Goose (Anser c. caerulescens)
The Lesser Snow Geese seen in Bering habitat all
nest on Wrangel Island north of Siberia and winter in
California, where they mix with a larger Canadian
nesting population. The long-term average figures in
Table 42-2 are misleading in that this population has
been in a decline and was thought to number 40,000
or less in 1978 (U.S. Fish and WildUfe Office, Port-
land, Oregon). They move north rather rapidly
in spring, but numbers are seen at the mouth of the
Kuskokwim and Yukon rivers in May.
In mid- to late September they make a rapid transit
from the Chukotsk Peninsula to the Seward Peninsula
and St. Lawrence Island, feeding on berries through-
out the month. Large numbers use the Clarence
Rhode Range, Nunivak National Wildlife Refuge, and
intertidal areas at Ugashik Bay on the Alaska Penin-
sula in late September and October before heading
southeast in late October.
748 Marine birds
There is considerable concern in the U.S.S.R. and
the U.S. for the welfare of this species, and hunting
restrictions are now in effect.
Aleutian Canada Goose (Branta canadensis leuco-
pareia)
This endangered species nests only in the outer
Aleutian Islands. It is thought to use estuarine habi-
tat there and further east as it migrates to California,
but the population is so reduced and other Canada
Geese so much more abundant that observations are
not conclusive. In May and June of 1978, four Aleu-
tian Geese were identified on the Pribilof Islands. One
of these had been banded on the nesting grounds of
Buldir Island in the Aleutians and another had been
banded in migration at Crescent City, California. The
second bird was with two unmarked birds (P.
Springer, personal communication). Reduced hunt-
ing in California and other management efforts under
the endangered species program are allowing the pop-
ulation to increase somewhat. Continued success may
result in important use of eastern Bering Sea habitats
by this bird.
Pintail (Anas acuta)
Pintails are the most abundant arctic nesting dab-
bUng duck and the farthest-ranging waterfowl in the
world (Bellrose 1976, Henny 1973). They are seen in
the Bering area moving north along nearshore leads in
the ice in April. Although intertidal nesting sites are
used, they are less significant for this species because
of its wide distribution on the uplands. Large num-
bers move to intertidal habitats after nesting. Great
flocks have been seen near the mouth of the Yukon,
on the tidal mud flats of Clarence Rhode Range, and
near Cape Newenham in midsummer, evidently feed-
ing on invertebrates or marine vegetation. A huge
freshwater fan extends far offshore at the mouth of
the Yukon River, supporting extensive beds of Pot-
amogeton filiformis, an important food of Pintails.
Some American wintering Pintails cross the Bering
Strait each summer to nest in Siberia.
Pintails are common in fall along the southeast
shore of the Seward Peninsula from Moses Point to
Golovnin Bay, from Kuskokwim Bay to Cape Peirce,
and along the Alaska Peninsula. Although Pintails
are always common in Bering habitats, large increases
are observed in years when drought conditions domi-
nate prairie nesting areas (Flock 1972, Henny 1973,
King and Bartonek 1977, Derkson and Eldridge
1978). Our figure of 1.222 million using Bering
habitats is based on the tundra nesting population of
Alaska and may be conservative (King and Lensink
1971).
Greater Scaup (Ay thy a marila)
The Greater Scaup is a common nesting species in
habitats bordering the eastern Bering Sea. Their cen-
ter of abundance is on the Yukon Delta. Densities
appear highest in the vegetated intertidal zone, where
up to 1.5 nests per km^ have been recorded.
Large numbers of male Greater Scaup begin to as-
semble in coastal bays and river mouths of the Yukon
Delta in late June and remain in the area until late
July. Large concentrations appear at the same time
on inland lakes on the delta (King 1973). In fall,
birds depart in a dispersed fashion, but make consid-
erable use of coastal bays and lagoons.
Common Eider (Somateria mollissima)
The Pacific race of the Common Eider, the largest
of the North American ducks, is common in coastal
habitats of the eastern Bering Sea. It commonly nests
in localized areas along the north side of the Alaska
Peninsula and the Yukon Delta. In the latter area it
occurs entirely within the vegetated intertidal, al-
ways vdthin 3 km of the beach. Densities averaging
approximately 12 nests per km' have been recorded
in this area.
Nonbreeding birds remain in flocks in nearshore
waters of the Bering Sea all summer; adult males join
them soon after their mates begin incubation. Small
flocks, predominantly males, are found during the
molt near coastal bays and lagoons from the Cape
Newenham /Hagemeister Island area north to Cape
Prince of Wales. Open rocky coastlines are sometimes
used in this area. South of Hagemeister Island, sum-
mer assemblages are found in veirious places. Adult
females and their young quickly move into nearshore
waters of Bering Sea after the hatching period, and
hence mixed flocks of this species are encountered
during fall migration.
During the winter, the Common Eider inhabits
nearshore waters of the Alaska Peninsula and Aleu-
tian Islands and, as ice conditions permit, ranges as
far north as the Bering Strait. There are usually open-
water areas in the winter south of Chukotsk Peninsula
near Nunivak, St. Matthew, and St. Lawrence islands,
and numerous open leads and polynyas at other _
northern Bering Sea locations. Nearshore waters of ■
the Pribilof Islands remain ice-free and support
wintering birds.
King Eider (Somateria spectabilis)
The King Eider does not nest in onshore areas of
the eastern Bering Sea, but winters in nearshore wa-
ters of the Alaska Peninsula, Aleutian, and Bering Sea
islands. Like the Common Eider, this species ranges
Waterfowl and their habitats 749
in winter as far north in the Bering Sea as ice condi-
tions permit.
In spring, King Eiders are seen in flocks of tens of
thousands in shallow waters of Bristol Bay and its la-
goons, and they pass the Yukon Delta in spectacular
numbers. Males predominate from late April through
May. Although open leads near shore form the pri-
mary pathways during spring migration, some flocks
take shorter routes (up to 15 km) from the beach. In-
land reports suggest that some birds may follow
routes through interior Alaska (Irving 1960).
In mid-September, adult female King Eiders and
their young have been seen in large numbers passing
east along the north side of Nunivak Island. By No-
vember this movement consists mostly of adult
males. No similar movement has been noted along
the coast of the Yukon Delta.
Spectacled Eider (Somateria fischeri)
The Spectacled Eider is an abundant nesting spe-
cies in the vegetated intertidal zone of the Yukon
Delta and may occur at other coastal locations north
to Bering Strait. Nesting has been recorded on St.
Lawrence Island (Fay and Cade 1959, Fay 1961).
North of the Bering Strait, the Spectacled Eider is an
abundant nester on the Indigirka River Delta in the
Soviet Arctic (Kistchinski and Flint 1974, Kistchinski
1973, Dau and Kistchinski 1977). On the Alaskan
side, nesting occurs at various locations east to the
Colville River (Bailey 1943, 1948).
Dau and Kistchinski (1977) reported nesting densi-
ties from 3 to 6.8 nests per km^ in the maritime prov-
ince of the Yukon Delta. This province roughly cor-
responds to the vegetated intertidal zone. A further
analysis of data from this area suggests that the aver-
age of 4.4 nests per km^ reported is very conservative.
The average density probably exceeds 9 nests per
km^ (C. Dau, unpublished data).
The distribution of the subadult and nonbreeding
components of the world Spectacled Eider popula-
tion is unknowoi. The distribution of breeding birds
and their young away from the nesting grounds is also
a mystery, with 14 scattered reports of adult birds be-
ing all the data available. Twelve of these reports are
from Bering Sea or nearby waters. This suggests that
in all likelihood Bering Sea habitats provide wintering
areas for most Spectacled Eiders. Dau and Kistchin-
ski (1977) present the belief that open-water areas in
the northern Bering Sea, including those south of the
major islands, support most, if not all, of the world
population in winter. Other eiders may also inhabit
these openings in the ice as well as areas south of the
ice where they are known to winter. The arrival of
most Spectacled Eiders on coastal areas of the Yukon
Delta from the north (Dau 1974, Dau and Kistchinski
1977), in striking contrast to the other eiders, rein-
forces statements to the effect that they may winter
in the north.
Steller's Eider (Polysticta stelleri)
Most Steller's Eiders nest north of the Bering Strait
along the coastal plains of the eastern Soviet Arctic
and Alaska. This species does not commonly nest on
the Yukon Delta, but is an abundant spring and fall
migrant in this and other habitats of eastern Bering
Sea. Steller's Eiders are found in spring and fall in
enormous flocks in the lagoons of Bristol Bay and the
Alaska Peninsula. A molt migration into this area
from northerly nesting and /or staging areas in the
Soviet Arctic and probably Alaska occurs in late sum-
mer (Jones 1965). Nearshore waters off Cape Newen-
ham, around Nunivak Island, and near Cape Avinof
support many birds of both sexes during the summer
and fall (Dick and Dick 1971; Petersen and Sigman
1976; C. Dau, unpublished data). In mid-September
adult females and their young have been recorded
passing east along the north side of Nunivak Island,
sometimes mixed with King Eiders.
In winter Steller's Eiders are common in the vicin-
ity of Kodiak Island, the south side of the Alaska
Peninsula, and the eastern Aleutian Islands. Along
the east coast of the Kamchatka Peninsula, the
Steller's Eider winters abundantly with Common and
King Eiders in the Karaginski Inlet (Gerasimov and
Vyatkin 1972).
Harlequin Duck (Histrionicus histrionicus)
The Harlequin Duck nests by the fast-running clear
streams associated with trout and greyling and is
never seen in the freshwater habitat associated with
most ducks. Since for this reason it does not appear
in normal breeding ground surveys, population figures
are speculative. Harlequins are never seen in migra-
tion, but after nesting they are found at the margin of
the sea, where they remain most of the year. They
are well camouflaged and hence difficult to see from
any distance. They are recorded throughout the
Bering Sea, often far from land, and around all the
islands. Recent observations have shown them to be
common in summer in marine waters around Nunivak
(Richie 1978) and near Cape Newenham (Dick and
Dick 1971, Petersen and Sigman 1976).
Oldsquaw (Clangula hyemalis)
The Oldsquaw is a circumpolar arctic tundra-
nesting species vdth ranges which extend into coastal
subarctic areas. This category includes coastal habi-
tats of the eastern Bering Sea of which the Yukon
750 Marine birds
Delta provides a majority of the preferred habitat.
The Oldsquaw is a common nesting species on the
delta and molts in large assemblages on inland lakes.
Huge numbers molt in nearshore waters of the Beau-
fort and Chukchi seas before moving south into the
Bering Sea. Many Oldsquaw appear to cross the Be-
ring Sea to the Okhotsk Sea, where they mingle with
the Siberian populations in winter (King 1973). Re-
nowned as deep divers, they are sometimes seen far
from land in winter and occur as far north in the Be-
ring Sea as ice conditions permit.
Black Scoter (Melanitta nigra)
The Black Scoter, largely a northwestern American
resident, is a common nesting species on the uplands
of the Yukon Delta. Few birds appear to nest in the
vegetated intertidal zone. Moving west and southwest
from the Alaskan nesting habitats in July, a large
component of this population mingles with other sco-
ters during the molting period. The molt occurs in
large flocks in nearshore waters from Cape Romanzof
to Kuskokwim Bay (C. Dau, in preparation) and
south to Cape Peirce (Dick and Dick 1971, Petersen
and Sigman 1976). During September and October
these assemblages begin departing from this area and
are found then along the south side of Bristol Bay
and in coastal lagoons. King and McKnight (1969) re-
ported some 180,000 scoters, mostly Black Sco-
ters, in the nearshore waters of Bristol Bay in October
1969. The nonbreeding segment of this population
apparently remains at sea all summer.
Surf Scoter (Melanitta perspicillata)
The Surf Scoter does not nest in coastal areas of
the eastern Bering Sea, but it is an abundant molting
species in nearshore waters of the Yukon Delta (C.
Dau, in preparation). From July through September
all three species of scoters are abundant in this area,
and the Surf Scoter greatly outnumbers the other two
species. Fall departure from the area appears to begin
in mid-September and may extend through October.
White-winged Scoter (Melanitta fusca)
The White-winged Scoter does not nest in coastal
habitats of eastern Bering Sea, but is common during
the summer and fall in nearshore waters of the Yukon
Delta (C. Dau, in preparation). In this area they are
the least common of the scoters, but Dick and Dick
(1971) found approximately equal numbers of White-
winged and Surf Scoters at Cape Peirce. Like the
other scoters present in these areas during the sum-
mer and fall, they appear to depart from mid-
September through October.
DISCUSSION
In revievdng this chapter, we may draw three ob-
vious conclusions: (1) knowledge of the details of
movements and distribution of birds in the Bering
Sea area is incomplete, (2) the dynamics of the inter-
tidal habitat is not well understood, and (3) the im-
pact of development or discharge of toxic substances
would endanger a large avian resource.
With more than nine million waterfowl heavily de-
pendent on Bering Sea habitats during their annual
cycle, the importance of this region is clear. That a
hundred percent of six species use the area each year
emphasizes its importance. Better information on the
distribution of waterfowl at sea and in the lagoons
and marshes of Bristol Bay and Norton Sound is
needed to help predict the effect of natural or man-
made events on the bird populations.
The 15,720 km^ of intertidal habitat found on the
eastern Bering Sea coast is probably not duplicated
elsewhere on the continent in an area of comparable
size.
The vast Yukon Delta supplies most of the vegeta-
ted intertidal habitat of the eastern Bering Sea. It is
not uncommon to find densities of nesting waterfowl,
primarily geese, in excess of 57/km^ in this habitat.
In some colonies much higher densities occur. Such
high production indicates that major storm surges
tend not to occur during the nesting season. Nearly
30 years ago biologists recognized these periodic
intrusions of the Bering Sea as important habitat-
altering mechanisms potentially very detrimental to
nesting birds. To date we have done little besides
providing rough appraisals of bird distribution,
abundance, and production vdth occasional qualita-
tive comments on the effects of storm-driven water.
The situation calls for an intensive geological apprais-
al of the effects of storm surges during various
seasons on (1) the distribution and characteristics of
the permafrost layer, (2) coastal and riverine erosion,
(3) lake formation (including thermokarst), and (4)
the dynamics of unvegetated mud flats.
Subtle, short-term alterations in habitat or produc-
tion can be analyzed annually. A more complete
appraisal of climatic, edaphic, and geologic proc-
esses is needed for comparative analysis of factors
affecting bird populations in the long term. Knovdng
the rate of terrestrial change would be important in
determining the ability of any species to adapt to
other habitat types.
It is clear that floating oil in the nearshore waters
or the principal lagoons of Bering Sea could destroy
large numbers of the nation's geese and diving ducks.
Similarly, oil cast by storm tides into the nesting
Waterfowl and their habitats 751
habitats of the Yukon Delta could be catastrophic to
the birds using this habitat.
ACKNOWLEDGMENTS
We are indebted to George Hunt, Jr., Dirk Derksen,
Robert Gill, John I. Hodges, Bruce Conant, Wilbur
Ladd, and Linda Dresch for helpful suggestions.
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I
Seetion ¥11
Interaction of Ice and Biota
Vera Alexander, editor
j
Ice-Biota Interactions: An Overview
V. Alexander
Institute of Marine Science
University of Alaska
Fairbanks
INTRODUCTION
I
Sea ice is an integral environmental feature in high
latitude marine areas and strongly influences the
biota in these waters. As a result, ecosystem strate-
gies have evolved to take advantage of ice and of its
potential for extending the growing season and pro-
viding a solid surface over large areas of the sea. Like
other such areas of the southern and northern high
latitude oceans, the Bering Sea is partly covered with
ice during the fall, beginning in October. The ice
reaches its maximum extent in early spring, and its
southerly extent has great significance to the biology
of the southeast Bering Sea shelf region. In cold
years, ice extends to a limit which coincides with the
shelf break, so that the entire large and wide shelf
system is ice-covered. This coincidence of the ice
edge with the shelf break is probably of vital sig-
nificance to the pelagic biological system in the area.
Furthermore, the Bering Sea is probably the only
seasonally ice-covered sea in which a shallow shelf
underlies the entire ice-covered zone, with rivers
contributing a large influx of fresh water and associ-
ated terrigenous materials.
This chapter serves to introduce a series of chap-
ters which will examine ice-biota interactions in the
Bering Sea. Although logistic support poses a prob-
lem in acquiring data during ice-covered periods,
over the years an impressive amount of information
has accumulated. In part this has resulted from the
use of "ships of opportunity," primarily icebreakers
operated by the United States Coast Guard in the
area on their ov^n missions. The accumulation of
data has notably accelerated recently under the
auspices of the Outer Continental Shelf Environ-
mental Assessment Program supported by NOAA,
especially in the marginal ice regions.
The presence of sea ice affects physical conditions
in the seawater beneath it through attenuation of
light and reduction of heat exchange, gas exchange,
and mechanical mixing. In this way, ice functions
primarily as a lid over the sea surface. At the same
time, it can serve as a floor. The upper surface of sea
ice is used as a habitat by a variety of birds and mam-
mals, and for many species of mammals in perma-
nently ice-covered areas it is their exclusive domicile.
The underside of the ice supports a spring community
dominated by diatoms, which grow within the micro-
cosm of the lowest portion of the ice in immediate
contact with the seawater. This community serves as
food for a variety of grazing animals, many of which
appear to be specifically adapted for life under the
ice, and which include the so-called cryopelagic
fishes. Ice-edge regions are another distinct environ-
ment; they can be considered as frontal systems with
a distinct horizontal gradient in temperature and sa-
linity. This is, of course, especially true during the
spring period, when rapid melting tends to produce a
low-salinity surface layer near the ice edge. The
stability of this system appears to play an important
role in initiating a spring bloom of phytoplankton in
the ice-edge region. This is essentially a classicad
bloom, triggered by the normal mechanisms such as
stable water column, adequate nutrients, and spring
light levels, but its time course is influenced strongly
by the intensity of the stratification, which is, at
least initially, primarily dictated by salinity gradients.
The shallow surface layer results in rapid nutrient
757
758 Interaction of ice and biota
utilization and exhaustion, and slow replacement
from below.
ORGANISMS ASSOCIATED WITH
SEASONAL SEA ICE
Ice flora
Epontic plant communities (i.e., those growing in
sea ice) are characteristic of sea ice in the spring
throughout all areas hitherto studied, and in both
antarctic and arctic waters such growth anticipates by
at least a month any significant primary production
by the phytoplankton in the water below the ice.
The occurrence of organisms growing in sea ice has
been observed since the middle of the nineteenth
century. Horner (1977) has recently reviewed the
background and recent development of our know-
ledge of ice algae, exploring in considerable detail the
structure of the communities, which seems to vary
considerably depending on the location. Even
between two successive seasons there can be differ-
ences in the dominant diatom species (Horner and
Alexander 1972). An interesting difference is ob-
served betv/een antarctic and arctic ice flora: in the
antarctic ice, maximum cell density often occurs in
the inner ice layers rather than at the bottom
(Buinitsky 1977). This may be because, as a result of
greater nutrient availability, the summer grovd;h
period is longer in the Antarctic, extending into
the fall; in the Arctic, the growth of algae in ice
follows a pulsed curve and the plants disappear in late
spring. Barsdate and Alexander (unpublished obser-
vations) noted that algal growth in association v^dth
ice continued into the late fall in the Antarctic
Peninsula waters near Palmer Station. Quantitative
work on photosynthetic rates of epontic communities
has been carried out in antarctic waters (Bunt 1963,
Bunt and Lee 1970) and in the Chukchi Sea (Horner
and Alexander 1972; Clasby et al. 1973; Apollonio
1961, 1965). The only previous work on ice com-
munities in the Bering Sea was that of McRoy and
Goering (1974). A chapter presenting the most
recent data from the Bering Sea is included in this
section.
The availability of nutrients in sea ice is of consid-
erable significance to the development and mainte-
nance of the epontic community as well as to phyto-
plankton living in the water in association with ice,
especially at the receding ice-edge in spring. Meguro
et al. (1967) suggested three mechanisms which can
supply the needed nutrients for algal growth: (a)
bacterial conversion of organic compounds in the ice,
(b) intrusion of seawater from under the ice into the
interstices between crystals, and (c) brine damage.
They conclude that the last mechanism is the most
likely, although more recent studies have suggested
that the seawater exchange could be more important
than has been recognized previously (Eide and Martin
1974). Eide and Martin demonstrated oscillatory
flushing of growing sea ice in the laboratory. This
flushing appears to be caused by internal brine
formation during freezing which leads to a "salt
oscillator" effect (Martin 1970). Thus, the brine
drainage and seawater intrusion mechanisms may be
closely related.
Ice-edge phytoplankton blooms
Spring ice-edge blooms are characteristic of areas
of unstable ice margin. As early as 1942, Hart ob-
served such blooms for the Antarctic, and described
the components as all neritic forms. Midttun and
Natvig (1957) found extremely large diatom popula-
tions near the ice during the Brategg expedition, with
a displacement of the maximum southward with
time. Hasle (1969) found more than 1.5 X 10^ cells/1
in mid-February at ice-edge stations, with a maximum
of 2.9 X 10^ cells/1. She considered the hydrographic
situation and possibly the supply of cells from the ice
responsible. Barsdate and Alexander (unpublished)
noted that ice margins in the Antarctic Peninsula re-
gion were in a bloom condition throughout late De-
cember, January, February, and even into March. In
the Arctic Ocean, there are no clearly unstable ice
margins such as those described for antarctic regions
above. However, the Bering Sea does represent a re-
gion with an extensive seasonal ice margin.
Goering and McRoy (1974) made a few measure-
ments of primary productivity along the Bering Sea
ice edge in spring. In our more recent Bering Sea
work, we have found the most intense production at
the ice edge just as the ice is breaking up. Three years'
coverage during the spring period as well as compara-
tive data from other times of year have given us a
rather detailed picture of the seasonal cycle; as a re-
sult, we have been able to estimate the contribution
of this spring ice-edge regime compared to that of
the southeast Bering Sea shelf for the remainder of
the year. The ice-edge bloom extends away from the
ice to a distance of 50-100 km, depending on the
rapidity of the ice retreat. The depth distribu-
tion of the phytoplankton varies with distance from
the immediate vicinity of the ice edge, and if the
bloom has been continuing for any length of time,
the cells tend to sink with distance from ice. This
phenomenon is presumably caused by nutrient
exhaustion at the surface, a conclusion which our
nutrient data support. Periodic resampling of an
active bloom region showed that the duration of high
I
i
i
i
Overview 759
photosynthesis is less than three weeks. Information
obtained on nutrient distribution suggests that silicon
depletion is a major limiting factor, although nitrogen
deficiency may also occur. Details of this bloom are
presented below.
Benthic communities
Although ice has an obvious effect on littoral ben-
thic communities, the direct effects on benthic com-
munities of the Bering Sea shelf are limited. In the
area under discussion here, the most important effect
of ice on benthos might be the supply of newly fixed
carbon as detritus from the epontic community and
from the ice-edge bloom. It is possible that much of
this material is not grazed in situ, and sinks to the
bottom. Part of it appears to remain potentially
active photosynthetically, and could rejoin the
pelagic system by means of wind mixing. How-
ever, it is probably available to the benthic communi-
ties. In particular, the ice-edge bloom develops so
rapidly in spring, because of the seeding by ice algae
and the extreme stability of the water column, that
grazing communities cannot respond in time to har-
vest much of the material. We hypothesize that a sig-
nificant portion of the organic carbon fixed at the
ice edge is contributed to the benthos.
Zooplankton
The ice algae serve as a source of concentrated
food for a variety of animals, including amphipods,
copepods, and ciliates, as well as juvenile and adult
fishes. In addition to this direct food-chain inter-
action, Cooney (1977) has noted that inverse strati-
fication associated with ice-cooled waters affected the
zooplankton community in the Bering Sea. A rela-
tively low diversity and sparse assemblage was found
in regions where the cold under-ice water mass ex-
tended to the bottom, and he noted a strong stratifi-
cation of the population at the ice edge when it ex-
tended to deeper water. He postulates that the cold
water blocks penetration of oceanic species into the
central shelf and coastal waters during the spring and
summer; although he considers ice per se to be of
little consequence, he believes that the process of
freezing and the effect of the pack on the under-ice
water mass do define some real biological boundaries
for most of the oceanic species (Cooney 1978). He
believes that the blooms at the ice edge benefit from
the absence of grazing pressure.
Birds and mammals
Strong evidence is presented below for a sharp
maximum in the distribution of marine birds in the
ice-edge region (Divoky, Chapter 47, this volume).
Although this does not appear to result from the ice
community as a source of food, the presence of the
surface adjacent to open water is probably of major
importance. Goering and McRoy (1974) mentioned
13 species of birds which occur in seasonal ice and in
permanent polar ice. The present study has extended
considerably the quantitative data on the occurrence
and feeding habits of birds in the ice-edge region of
the Bering Sea.
Unlike birds, which largely nest in coastal regions
or on islands, many marine mammals produce their
young on ice. For example, spotted seals (Phoca vitu-
lina largha) are concentrated during the periods of
birth and nurture of pups in the ice-edge zone of the
seasonal pack ice. Seals with pups spend much of the
time on the ice (Burns 1970). Ribbon seals (Phoca
fasciata Zimmerman) are associated with the ice
front in the Bering Sea during the winter and spring,
and require open water or thin ice. Beluga (Delph-
inapterus leucas (Pallas)) and narwhal (Monodon
monocerus (L.)) also inhabit the ice edge. Beluga
of the Bering Sea winter along and in front of the
seasonal sea-ice pack, since they cannot make holes in
any but the thinnest ice cover. According to Goering
and McRoy (1974), walrus (Odohenus rosmarus
(L.)), beluga, ringed seal (Phoca hispida Schreber),
and bearded seal (Erignathus barbatus Erxleben) stay
with the ice edge as it annually advances and retreats.
Burns (1970) has pointed out that the reproductive
cycles and structure of these mammals are specifical-
ly adapted to ice. For example, walrus and bearded
seal have massive skulls, the claws of phocids in ice
are large, and the coloration is often an off-white,
which provides protection in this environment. For
these animals, ice clearly provides advantages which
include isolation, space, food supply, transportation,
sanitation, and shelter.
Fay (1974) summarizes the role of pack-ice in the
Bering Sea in marine mammal ecology:
The ice pack of the Bering Sea is a major component of
the habitat of about one million mammals .... It is
widely recognized that the ice of this and other subpolar
and polar seas is important to such mammals in two
ways; first, it serves as a substrate on which pinnipeds
haul out to sleep and bear their young, and second, it
forms a rigid barrier though which pinnipeds and ceta-
ceans alike must find or make holes in order to have
access to the air they breath [sic] and the sea that holds
their food.
Clearly, the ice edge represents a compromise in this
regard, and eliminates the need to create holes.
The Outer Continental Shelf Environmental Assess-
ment Program has made it possible to acquire a con-
siderable volume of new data on bird and mammal
760 Interaction of ice and biota
distributions in the Bering Sea, including tlie ice- Bunt, J. S.
covered regions. Of special interest is new informa- 1963
tion on the tremendous importance of polynyas;
much more study is needed in order to determine all
their characteristics. Residual ice regions after the ice
pack has retreated are also important to marine mam-
mal populations. These and other phenomena related
to the significance of sea ice to Bering Sea birds and
mammals will be discussed in the chapters below by
Divoky and Burns.
Diatoms of antarctic sea ice as agents
of primary production. Nature 199:
1255-7.
Bunt, J. S., and C. C. Lee
1970 Seasonal primary production in ant-
arctic sea ice at McMurdo Sound in
1967. J. Mar. Res. 28: 304-20.
DISCUSSION
Burns, J. J.
1970
In view of the extreme importance of sea ice to the
biological regimes of the Bering Sea, involving all tro-
phic levels from phytoplankton to birds and mam-
mals, this synthesis of currently available information
is timely. Further examination of the effects of pol-
lutants on this ice-biota community is needed; but
some help is provided by other sections of this book,
especially the chapter dealing with the behavior of
hydrocarbons in relation to ice (Martin, Chapter 14,
Volume 1). Further work defining the potential pol-
lution of the benthos through plankton or ice algae Cooney, R. T.
would be a useful addition, as would the microbio- 1977
logical component of ice-related systems, which is
undoubtedly important and deserves examination in
depth. The generalization often made that more
questions are raised than are answered by any compo-
nent piece of work is true for the range of ice-related
topics discussed here.*
Remarks on the distribution and natu-
rcd history of pagophilic pinnipeds in
the Bering and Chukchi Seas. J. Mam-
mal. 51: 445-54.
Clasby, R. C, R. Horner, and V. Alexander
1973 An in situ method for measuring pri-
mary productivity of arctic sea ice al-
gae. J. Fish. Res. Bd. Can. 30: 835-8.
Zooplankton and micronekton studies
in the Bering-Chukchi/Beaufort Seas.
In: Environmental assessment of the
Alaskan continental shelf. NOAA/
OCSEAP, Ann. Rep. 10:275-363.
REFERENCES
1978 Environmental assessment of the
southeastern Bering Sea: zooplankton
and micronekton. In: Environmental
assessment of the Alaskan continental
shelf. NOAA/OCSEAP, Final Rep.
1:238-337.
ApoUonio, S.
1961 The chlorophyll content of arctic sea
ice. Arctic 14: 197-9.
1965 Chlorophyll in arctic sea ice. Arctic
18: 118-22.
Buinitsky, V. K.
1977 Organic life in sea ice. In: Polar
oceans, M.J. Dunbar, ed., 301-6. Arc-
tic Inst. N. Amer.
*Contribution No. 421, Institute of Marine Scienc'o^ Univ-
ersity of Alaska, Fairbaniis.
Eide, L. I., and S. Martin
1974 The formation of brine drainage fea-
tures in young sea ice. J. Glaciol. 14:
137-53.
Fay, F. H.
1974
The role of ice in the ecology of ma-
rine mammals of the Bering Sea. In:
Oceanography of the Bering Sea, D.W.
Hood and E.J. Kelley, eds., 383-99.
Occ. Pub. No. 2, Inst. Mar. Sci., Univ.
of Alaska, Fairbanks.
Overview
761
Goering, J. J.
1974
Hasle, G. R.
1969
and C. P. McRoy
Sea ice and under ice plankton. In:
Coastal ecological systems of the
United States, H.T. Odum, B.J. Cope-
land, and E.A. McMahan, eds., 55-70.
The Conservation Foundation, Wash-
ington.
An analysis of the phytoplankton of
the Pacific Southern Ocean: Abun-
dance, composition, and distribution
during the Brategg expedition, 1947-
1948, Hvalrad. Skr. 52: 1-168.
Martin, S.
1970
McRoy, C. P.
1974
A hydrodynamical curiosity: The salt
oscillator. Geophys. Fluid Dynamics
1: 143-60.
and J. J. Goering
The influence of ice on the primary
productivity of the Bering Sea. In:
Oceanography of the Bering Sea,
D. W. Hood and E. J. Kelley, eds.,
403-21. Inst. Mar. Sci., Occ. Pub.
No. 2, Univ. of Alaska, Fairbanks.
Horner, R.A.
1977 History and recent Advances in the
study of ice biota. In: Polar oceans,
M.J. Dunbar, eds., 269-84. Arctic
Inst. N. Amer.
Meguro, H., K. Ito, and H. Fukushima
1967 Ice flora (bottom type): a mechanism
of primary production in polar seas
and the growth of diatoms in sea ice.
Arctic 20: 114-33.
Horner, R. A., and V. Alexander
1972 Algal populations in arctic sea ice: An
investigation of heterotrophy. Limnol.
Oceanogr. 17: 454-8.
Midttun, L., and J. Natvig
1957 Pacific antarctic waters.
Brategg Exped. 3: 1-130.
Sci. Res.
Primary Production
at the Eastern Bering Sea Ice Edge:
The Physical and Biological Regimes
H. J. Niebauer, V. Alexander, and R. T. Cooney
Institute of Marine Science
University of Alaska
Fairbanks, Alaska
ABSTRACT
In this chapter, we show that the melting of the ice edge in
the Bering Sea promotes high primary production in spring
by increasing the stability of the water column. Hydro-
graphic sections of temperature, salinity, sigma-t, nitrate,
ammonia, and chlorophyll a through the ice-edge zone in the
spring of 197 5, compared with sections taken later in the
spring, seem to support this hypothesis. In addition, sections
collected at similar times in spring 1976, a relatively cold year,
and spring 1977, a relatively warm year, suggest that short-
term climatic fluctuations may control the nutrient supply at
the ice edge. In warm years the ice is farther up on the shelf,
away from the nutrient -rich Alaska Stream/ Bering Sea water
mass, a condition which may be important to upwelling
phenomena at the ice edge. Finally, we present a conceptual
model depicting the flow of organic matter relative to the
timing of the ice melt and seasonal variations in the position of
the ice edge.
INTRODUCTION
The southeast Bering Sea shelf is a relatively
shallow (shelf break ~150 m) but wide (~500 km)
region, seasonally covered with ice. During a typical
winter, the ice advances about 1,000 km southward
from the Bering Strait to the shelf break, primarily by
freezing within the Bering Sea (Leonov 1960),
rather than by advective advance through the Bering
Strait (Tabata 1974). Ice appears to be generated at
south-facing coasts along the northern Bering Sea
coast— for example, near Nome in Norton Sound.
North winds apparently blow ice away from these
coasts and new ice is formed at the coast in the
manner of a conveyor belt, moving southward until
the ice edge starts to melt at its southern extent
(Pease, Chapter 13, Volume 1). During most of the
ice season, there should be increased stratification in
the water column at the ice edge because of the
constantly melting ice. In spring, about 63 percent of
the ice melts within the Bering Sea basin (Lisitsyn
1960), and the remainder leaves the basin through the
various passes and straits.
The melting ice has marked effects on the physical
and biological regimes at the ice margins. Marshall
(1957) hypothesized that the observed high spring
primary productivity near the retreating Bering Sea
ice edge is due in part to increased stability in the
water column resulting from the low salinity of the
meltwater. Observations by McRoy and Goering
(1974) and Alexander and Cooney (1978) support
this hypothesis (Alexander and Niebauer 1980). Hart
(1942) and Ivanov (1964) have observed similar
phenomena in antarctic waters. Saito and Taniguchi
(1978) and Hameedi (1978) concluded that some of
the plankton at the ice edge are algal cells from
populations growing within the sea ice. However,
Horner and Alexander (1972) have not found ice
algae in the water column after breakup in the
Chukchi Sea.
In this chapter we show that the melting ice mar-
gin in the Bering Sea is the site of an intense phyto-
plankton bloom, and we document some aspects of
its distribution in time and space. We suggest, on the
basis of data covering the periods of spring ice-
retreat in 1975-77, that the spring ice-edge bloom is
a characteristic spring bloom, intensified in time and
space by the influence of the ice edge on the physical
structure of the water column and the marked change
in light regime as the ice breaks up. This bloom
accounts for a significant proportion of the annual
primary production on the Bering Sea shelf. It is
probable that the production exceeds the demand in
the water column for particulates during the bloom
and that a large percentage of the material falls to the
sea bed, as happens in most shelf systems with
763
764 Interaction of ice and biota
seasonal pulses in primary production (Walsh et al.
1978). However, the system differs from that in the
New York Bight, for example, in that the ice attenu-
ates mixing and wind stirring, thereby increasing the
effects of water column stability both in enhancing
the phytoplankton bloom and in limiting nutrient
replenishment.
METHODS
A series of cruises was conducted at the ice edge
from May 15 to June 9 in 1975, from March 14 to
April 30 in 1976, and from April 7 to June 11 in
1977. The strategy employed was to occupy stations
at intervals of about 10 km along courses roughly
perpendicular to the ice edge, extending into the ice
when possible and away from the ice for about 50
km. Standard hydrographical sampling using Series
9000 Plessy CTD systems was done at each station.
The data obtained were calibrated using in-situ
water samples. Chlorophyll a was measured by ex-
tracting particulate material collected on micropore
glass filters in 90 percent acetone over a 24-hour
period and reading the absorbance of the extract vdth
a Beckman DU spectrophotometer. In 1977 fluores-
cence of the extract was determined with a Turner
fluorometer.
RESULTS
Ice-edge hydrography
The dramatic fluctuations in sea temperatures and
southern extent of the ice on the eastern Bering Sea
shelf as related to anomalous weather patterns have
been outlined by Niebauer (1980; Chapters 3 and 9,
Volume 1). We are concerned here with the effect of
these fluctuations on the hydrographic sections of the
ice edge collected on cruises in late May 1975 and
late March-early April 1976 and 1977. In May 1975,
sea-surface temperatures (SST) around the Pribilof
Islands were ~2.8 C below normal at ~0.2 C, and the
ice cover was about 15 percent above the normal
coverage 30-35 percent (Niebauer 1980). The posi-
tion of the ice-edge section is showTi in Fig. 44-1
to be up on the shelf north of the Pribilof Islands.
In late March 1976, sea-surface temperatures were
still ~1.7 C below normal at —0.5 C, and the ice
cover was 15 percent above the normal coverage of
60-65 percent for late March (Niebauer 1980). The
156
>b 0
20 «0
60 80
lOO'.m
Figure 44-1. Southeast Bering Sea showing locations of cruise transects through the ice edge. Ice-edge envelopes show
maximum and minimum southern ice extent during cruise. Redrawn from Alexander and Cooney (1979).
Primary production 765
ice is anomalously far south (Fig. 44-1), almost over
the shelf break south of the Pribilof Islands. Finally,
in early April 1977, only a week later than the pre-
vious year, SST was higher (~1.0 C or an estimated
0.8 C above normal) and the ice cover about 10
percent below the normal 60 percent (Niebauer
1980). Fig. 44-1 shows the position of the section
taken across the ice edge that has retreated over
the shelf, relative to the position of the ice edge at
the same time in the previous year.
The position of the temperature, salinity, and
sigma-t sections (Figs. 44-2a, b, and c) for 1975 is
shown in Fig. 44-1 to be far up on the shelf. The
ice-edge temperatures are on the order of -0.5 to
— 1.3 C but they decrease with depth to —1.6 to
— 1.7 C at 65-70 m. Farther away from the ice, the
sea-surface temperatures reach 0.1 C. Salinities in
the ice are on the order of 31.2*^/oo, increasing with
depth to 32.0°/oo at the bottom, and with dis-
tance away from the ice to a maximum of 31.8^/oo.
The thermocline, halocline, and hence pycnocline
are at 20-30 m, extending throughout the section,
although they are most developed at and within the
ice edge. All the water found in this cross section is
the shelf water (<32.0O/oo, -2-10 C) described by
Coachman and Chamell (1979).
OPEN WATER
OPEN WATER
r}}nnnnnn}}}rfn)nn)>}fnnm.
^"^^nrrr^jj^^rrrrrrrrrmrTrrmrrT
i}ii I iiDiinii iiniiiiiii I iin iiiin,
''^''''^nTrrrT^rrTrrTrrrrrrrrrrrnrTrrT
TEMPERATURE. C
CRUISE DS808 1
Station Numb«r
OPEN WATER
f}}n})))innn))!}inn>n!nn}iunn
CRUISE DS808 1
Slation Numbor
OPEN WATER
;!!)}>} >))}}nn)unn>nn}})n}))nfr,
'^'-^^Trrrrj^^jrrrrrrmTmTrTTTrrrT
32 31
OPEN WATER
}!n>} iunnn) mffnnn nin njuh
'''''''^rTrrj^.^^^.jrrTrTTTTTTTTTTTTTTnrr
OPEN WATER
30 29 26
rnnninnnn))>n)}>}nn'nunnun
'^"^^nr^^^yrrrr^rfrrmrrrmTTrTTT
CRUISE DS808 1
CRUISE DSSOfl 1
Figure 44-2. Temperature (a), salinity (b), sigma-t (c), chlorophyll a (d), nitrate (e), and ammonia (f) cross sections taken
along the 1975 transect shown in Fig. 44-1. Open-water, ice-edge zone, and ice-pack stations are indicated. Redrawn from
Alexander and Cooney (1979).
766 Interaction of ice and biota
The salinity and sigma-t sections (although not the
temperature) suggest upwelling around stations
27-29. The wind data suggest that there may have
been off -ice Ekman transport leading to upwelling.
The sections for 1976 are farther south near the
shelf break (Figs. 44-1, 44-3a, b, and c). The shape of
the isotherms in the upper layer (0-60 m) is similar to
that in 1976, as are the ice-edge temperatures. How-
open WATER
Station Number 162 174
7777777777T777777777777
rrrrrrr^
Tmrrrr
180"- ^
TEMPERATURE. C CRUISE SU1 MARCH APRI L 1976
iCE OPEN WATER
Station Number 162 174
-ir-
194
199 200
Tm-rm ! I > n i ) I / niTTTrT'^'^''^
innin
OPEN WATER
Station Number 162 174
-ir-
194
199 200
777777777777777777777
Trrrrrrrr^
Tmrrrr
SALINITY.%c
Station Number 162 174 0 6
MARCH APRIL 1976
OPEN WATER
7777777777777777
TrTTrrrrTrrrr^
mm n
CRUISE SU1
MARCH APRIL 1976
CHL.i(^qA) CRUISE SUl
MARCH APRIL 1976
Station Number 162 174
Or
OPEN WATER
—11—
194
199 200
rrrTTTTmrrTTTTrP'^'^
1/ nil ) I
CRUISE SUl
MARCH APRIL 1976
OPEN WATER
Station Number 162 174
Or
199 200
Ci3
rTTTnmri I ' 1 1 1 rrrrmTTr^'^
mill I >-
CRUISE SUl
MARCH APRIL 1976
Figure 44-3. Temperature (a), salinity (b), sigma-t (c), chlorophyll a (d), nitrate (e), and ammonia (f) cross sections taken
along the 1976 transect shown in Fig. 44-1. Open-water, ice-edge zone and ice-pack stations are indicated. Redrawn from
Alexander and Cooney 1979).
Primary production 767
ever, the vertical temperature gradient is reversed.
There is now a strong thermocline much deeper, at
70-90 m, with Alaska Stream /Bering Sea source water
(T = 3-4 C) below. The salinity data display similarly
low salinity (31.7°/oo) at the ice edge, increasing
both with distance from the ice and with depth. A
strong halocline is present at 70-90 m with the Alaska
Stream/Bering Sea source water (salinity >32'^/oo)
beneath. The density data also show the strong
pycnocline at 70-90 m.
The salinity, temperature, and sigma-t sections all
suggest upwelling around station 199. The wind data
collected aboard ship suggest there may have been
off -ice Ekman transport leading to upwelling.
The 1977 data were obtained from a much longer
section (Figs. 44-1, 44-4a, b, and c) ranging from off
the shelf to the 40-m isobath. The ice-edge tempera-
tures (—1.4 C) and salinities (31.6°/oo) are similar
to those of 1975-76. The water out to about station
19 looks vertically mixed with a horizontal gradient,
giving the appearance of a rather diffuse frontal zone
(see Schumacher et al. 1979). The two front systems
described by Coachman and Charnell (1979) are
apparent, with the inner front in temperature and
salinity on the bottom between stations 19 and 20.
The outer front is evident (especially in salinity
values) in the surface layers between stations 20 and
21. The whole shelf section, except right at the ice, is
much warmer than in the previous years. Especially
remarkable is the core or layer of water of more than
4 C running up on the shelf at about 100 m.
Ice-edge primary production
The most intense primary production occurs at the
ice edge just before breakup. Three years' coverage
during the critical spring period, as well as compara-
tive data from other times of year, have given us a
rather detailed picture of the seasonal cycle; and as a
result of this, we have been able to estimate the
contribution from this spring ice-edge regime com-
pared with that from the remainder of the year on
the southeast Bering Sea shelf. Surface chlorophyll a
values frequently exceeded 20 mg/m^ and primary
productivity exceeded 25 mg C/m^ /hr; although such
rates were not sustained for a very long period of
time, a substantial contribution is possible due to the
intensity of the photosynthetic activity. Resampling
of a bloom area showed that chlorophyll a had
declined to an average of less than 1 mg/m^ in less
than three weeks.
The peak of the ice-edge bloom occurs in late May,
only a little after the peak of the open-water bloom
in late April to early May. Although the peak of the
ice-edge bloom occurs later, activity along the ice
edge is already well above standing winter levels in
March, when open-water productivity is minimal.
The ice-edge bloom extends away from the ice to a
distance of 48-80 km, but the depth structure of the
activity as well as the population composition
changes with distance from the ice edge. Fig. 44-5
shows depth profiles of primary productivity and
chlorophyll a at three stations along a transect during
the May 1975 Discoverer cruise. The activity near the
surface was high, but the chlorophyll a concentration
had dropped considerably 40 km from the edge.
We have looked at the structure of the water col-
umn along transects intercepting the ice edge. It
becomes clear that there is a shallow zone (less than
30 m in depth) which is under the influence of ice,
regardless of the physical regime in the area of the
ice edge. In Figs. 44-2, 44-3, and 44-4 we have
plotted the information for selected transects sam-
pled during the three years. The position of the ice
edge varied in the three years, partly because of the
different temperature regimes, but also to some
extent because of the timing of the surveys. The
1975 transect shows that near the ice edge the sea
temperature dropped with depth, and there is no
evidence that nutrient-rich source water intruded
under the ice-dominated water. In 1976, the more
usual situation of an increase in temperature vdth
depth occurred, and at 90 m there was a thermocline
with nutrient-rich source water evident below it. To
some degree the apparent anomaly in 1975 could
have been caused by the fact that the 1975 transect
was done at a time when the ice was much farther
north on the shelf. The biological data show that the
bloom had progressed further during 1975, since the
chlorophyll a was very high and the nitrate levels near
the ice edge had been reduced significantly. In the
1977 transect the ice is far to the north, this time due
to very light ice conditions and a high sea-surface
temperature. This very long section extends far out
towards the shelf break, and the transect shows
clearly the location of the major fronts and the warm
source water appearing over the edge of the shelf. The
ice-edge bloom is not very intense at this time, in
comparison to the 1975 transect, but it is in the early
stages of development and has already caused a
decline in nitrate concentrations near the ice edge.
The phytoplankton bloom, then, develops in the
surface layers in the immediate vicinity of the ice.
Where the ice-edge bloom has been in progress for
some time and the ice is receding, the chlorophyll
a, as distance from the ice increases, tends to be
somewhat mixed dovm into the water column with a
less distinct maximum and a more even distribution
throughout the surface waters.
768 Interaction of ice and biota
The information obtained on nutrient distributions
strongly suggests that depletion of nitrate is a major
factor limiting spring production, especially at the
ice edge. Nitrate concentrations in spring, at the
beginning of the bloom period, are uniform with
depth, although somewhat lower in the ice-covered
areas (5-15 /ug at/1) than in the open water (15-25
/jg at/1). Although the differences in ammonia
ICE-EDGE ZONE
Figure 44-4. Temperature (a), salinity (b), sigma-t (c), chlorophyll a (d), nitrate (e), and ammonia (f) cross sections taken
along the 1977 transect shown in Fig. 44-1. Open-water, ice-edge zone and ice-pack stations are indicated. Redrawn from
Alexander and Cooney (1979).
Primary production 769
16 16 20 22 24 26 29 30 ^^'' '^*" «
■"■ ' ""TTT 1 1 I ' ^g C/(/)(hf)
/ SURVEYOR 2
/ ICE TRANSECT II
^■a
I Q Station 13 in ice
t O Station 14 ice-edge
k A Station 15 out of ice
—— Chloroptiyll
Primary Productivity
Figure 44-5. Depth profiles of primary production and
ciiioropiiyll a at three stations at different distances from
the ice edge. Redrawn from Alexander and Cooney (1979).
concentrations are not so distinct, the general trend
appears to be the opposite— ammonia concentrations
are higher in ice-covered areas than in the open water.
As the bloom progresses, after stratification is estab-
lished near the ice edge, ammonia concentrations
tend to increase. An increase is also evident in areas
of open water. Although the source of this increase
is not clear, in ice-dominated areas in-situ ammoni-
fication may be the mechanism.
Ice-edge model
The general elements of the ice-edge ecosystem
can be described in a spatial and temporal concep-
tual model (Fig. 44-6). The proximity of the ice-edge
zone to the shelf break in the southeast Bering Sea
depends on the severity of the preceding winter; the
duration and strength of the seasonal cooling cycle
determines the location of the southern terminus of
the pack. There is increasing evidence that cycles of
water temperatures are related to fluctuations in the
long-term atmospheric circulation over the northern
North Pacific Ocean (Niebauer 1980; Chapters 3 and
9, Volume 1). For periods of one or more years, the
atmospheric distribution of spatial pressure patterns
forms a predominantly southerly or northerly mean
air flow above the ocean surface. If the air flow is
mainly southerly, the winters are warm and the
seasonal ice is restricted to northern shelf regions.
During periods of mean air flow from the north, the
converse is true: the cooling cycle is longer and more
intense, influencing waters farther to the south.
During these years, the ice-edge zone may extend as
far as the shelf break and, under some wind condi-
tions, beyond. The ice may persist over some por-
tions of the shelf through late spring and early sum-
mer.
In midwinter, v^dth snow cover and low incident
incoming radiation, the ice pack acts as an extremely
effective shade for the underlying water column.
It is not until late winter and early spring that enough
light penetrates to promote the growth of the algal
community living in the lower portions of the sea
ice. This event marks the beginning of the annual
production cycle in the region. In our work we have
observed chlorophyll a levels as high as 70 mg/m^
of sea ice, although the distribution of the chloro-
phyll is very patchy. It is possible that the material
produced in the ice is grazed, either while still in
position by juvenile fishes, amphipods, and poly-
chaetes, or by the planktonic community as the ice
disintegrates, releasing the cells into the water.
However, although we have no quantitative informa-
tion on this, it is reasonable to assume that at least
part of the carbon finds its way to the benthic
environment.
Closed pack Edge zone
Open water
SEASONAL MODEL
1000-
E 800
0)
^ 600
o
O 400
200
Late winter
Mid-winter
SPATIAL MODEL
RELATIVE TO OCEANIC
AND SHELF REGIMES
ORGANIC MATTER PARTITIONING MODEL
Oceanic
I Primary Production
I
Pelagic
Herbivores
Benthos
I
Primary Production
Micronekton
Pelagic Fishes
I
Pelagic
Herbivores
f
Micronekton
Pelagic Fishes
, i ,
I Sea Birds |
Sea Birds
Mammals
Demersal Fishes
Marine Mammals
Figure 44-6. Conceptual model of the ice-edge ecosystem
depicting the seasonal variations in plant stocks, the posi-
tion of the edge zone relative to the shelf and oceanic
waters, and the flow of organic matter in pelagic food webs.
Redrawn from Alexander and Cooney (1979).
no Interaction of ice and biota
Further increases in radiation allow a bloom to
begin under the ice and in the open water south of
the edge zone. However, the most dramatic event
does not occur until the edge begins to break up
over wide areas of the shelf.
As the ice separates into smaller floes, light pene-
tration into the sea increases significantly while, at
the same time, the partial ice cover continues to keep
wind mixing at a minimum. Under these condi-
tions, an extremely intense bloom occurs. Nitrate
concentrations of up to 18 jug at /m-' and the stable
shallow surface layer under the direct influence of
the ice set the optimal conditions. The bloom is
short lived , probably persisting for only two weeks
or so. The distribution of this activity over the
Bering Sea shelf depends on the mode of ice dis-
integration, but we assume that the ice breaks up
over a considerable area simultaneously. The bloom
extends as far as 50-100 km from the ice edge,
decreasing in intensity with horizontal and vertical
distance. It reaches its greatest intensity within the
ice pack, where carbon fixation rates as high as 600
mg C/m^ /hr have been measured at 32 km, and 725
mg C/m^ /hr at 48 km, into the broken ice during an
April cruise. We do not know whether the up welling
described above is a major factor in the primary pro-
ductivity regime near the ice edge, but it seems
reasonable to assume that it does contribute.
An open-water bloom occurs away from the ice
edge in response to the balance between light and
stability, as observed elsewhere in the northern North
Pacific. Sixty-five percent of the annual primary
production on the Bering Sea shelf occurs during the
months of April, May, and June (Alexander and
Cooney 1979).
The transfer of organic matter formed at the ice
edge to primary consumers or higher trophic levels
depends upon the structure of the grazing com-
munity of the underlying water column. During
cold years, when the edge extends to the oceanic
water mass, the early portion of edge-zone bloom is
grazed by a diverse and abundant assemblage of
copepods characterized by the immature and adult
forms of Calanus plumchrus, C. cristatus, Eucalanus
h. bungii, Metridia lucens, and Pseudocatanus spp.
These copepods range in length from 0.7 to 8.0 mm
and are capable of ingesting most of the wide spec-
trum of particle sizes associated with the bloom. As
a result, a relatively large percentage of the water
column production and ice-related production is
incorporated into a pelagic food web (Fig. 44-6).
During relatively warm years or after the north-
ward recession of the ice edge over the shelf, the
grazing community of the water column changes in
composition. The shelf copepods are numerically
dominated by three small taxa, Acartia longiremis,
Pseudocalanus spp., and Oithona similis. These
organisms, along with Calanus marshallae and C.
glacialis, seem to be considerably less efficient than
the larger species at harvesting the organic matter in
this region, most of which settles to the bottom (Fig.
44-6).
The recession of the edge must also affect the
type, availability, and abundance of food for birds
and marine mammals using the edge zone in the
spring. Shipboard observations of bottom-trawl
catches and the results of occasional midwater
trawling, coupled with onsite stomach analyses,
demonstrated that the food composition differed
with location along the edge zone. At stations shal-
low enough not to be influenced by oceanic water
(~70 m or less), walleye pollock were generally
replaced by capelin; and Parathemisto libellula,
a large hyperiid amphipod, became more abundant.
Also, the dominant euphausiid over the outer shelf,
Thysanoessa longipes, was replaced by T. inermis and
T. raschii over the shallower regions of the shelf.
Except for the auklets, birds and mammals along the
edge zone fed on micronekton (euphausiids and
amphipods) and fishes which were one year old or
older. Thus, most of the forage species for higher
trophic levels are survivors from the previous year's
production cycle and occur independently of current
conditions.
CONCLUSIONS
Hydrographic sections collected across the ice-
edge zone in spring of 1975-77 were analyzed in con-
junction with both the large-scale (months /years)
atmospheric flow patterns (Niebauer, Chapter 3,
Volume 1) and ice extent (Niebauer, Chapter 9,
Volume 1) in this region. Winter large-scale atmos-
pheric circulation appears to be the driving force for
fluctuations in sea temperatures and ice coverage in
the Bering Sea. These winter atmospheric conditions
or events may have considerable effect on the ice-
edge bloom phenomena. First of all, in cold years
(e.g., 1975 and 1976), the ice edge is nearer the shelf
break (i.e., near the more nutrient-rich water) when
the spring melt begins. This can mean a more plenti-
ful supply of nutrients for an ice-edge bloom no
matter how the bloom is initiated and maintained
(by melting ice, ice-edge upwelling: see Buckley
et al. 1979). The converse may be true in warm
years (e.g., 1977) when the ice edge is far up on the
shelf in shallow water where nutrients may be used
up quickly, especially in the very wide but shallow
Bering Sea shelf.
Primary production 771
Melting of sea ice in the ice edge is not the only
possible mechanism for producing conditions con-
ducive to a bloom. Storm systems crossing the
ice edge can grind up ice into frazil or slush ice which
damps waves, stabilizes the water column, and allows
increased solar radiation to pass through the ice.
With appropriate nutrients a bloom is initiated.
Blooms initiated in slush ice formed by a storm
passing over the Bering Sea ice edge have been ob-
served by Chapman and Alexander (personal ob-
servation).
Alexander, V., and H. J. Niebauer
1980 Primary productivity in the Bering
Sea ice edge in spring: II. Biology.
Unpub. MS.
Buckley, J. R., T. Gammelsr0d, J. A. Johannessen,
O. M. Johannessen, L. P. R0ed
1979 Upwelling: Oceanic structure at the
edge of the arctic ice pack in winter.
Science 203:165-7.
ACKNOWLEDGMENTS
The work discussed here was carried out on board
the NO A A ships Discoverer, Surveyor, and Miller
Freeman. Much of the work at sea, as well as sample
analysis and synthesis, was carried out by T. Chap-
man and D. Brickell.
This work was supported primarily by the National
Oceanic and Atmospheric Administration Outer
Continental Shelf Environmental Assessment Pro-
gram, contract number 03-5-022-56. Support was
also provided by the National Science Foundation
Grant DPP 76-23340 A02 (PROBES), the Alaska
Sea Grant Program, cooperatively supported by
NOAA National Sea Grant College Program, United
States Department of Commerce, under Grant
NA79AA-D-00138, and the University of Alaska
with funds appropriated by the State of Alaska. This
is Contribution No. 422, Institute of Marine Science,
University of Alaska, Fairbanks.
Coachman, L. K., and R. L. Charnell
1979 On lateral water mass interaction— a
case study, Bristol Bay, Alaska.
J. Phys. Oceanogr. 9:278-97.
Hameedi, M. J.
1978 Aspects of water column primary pro-
ductivity in the Chukchi Sea during
summer. Mar. Biol. 48:37-46.
Hart, T. J.
1942
Phytoplankton periodicity in antarctic
surface waters. Discovery Reports
21:261-356.
Horner, R., and V. Alexander
1972 Algal populations in arctic sea ice:
An investigation of heterotrophy.
Limnol. Oceanogr. 17:454-8.
Ivanov, A. I.
1964
REFERENCES
Alexander, V.
1978
1979
and R. T. Cooney
Bering Sea ice edge ecosystem study:
Nutrient cycling and organic matter
transfer. In: Environmental assess-
ment of the Alaskan continental
shelf, NOAA/OCSEAP, Ann. Rep.,
6:216-448.
Ice edge ecosystem study: Primary
productivity, nutrient cycling and or-
ganic matter transfer. Environmental
assessment of the Alaskan outer
continental shelf, Final Rep.
Characteristics of the phytoplankton
in antarctic waters at the whaling
grounds of the flotilla Slava in 1957-
58. Soviet Antarctic Exped. Inf.
Bull. (Transl. ) 1:394-6.
Leonov, A. G.
1960 Regional oceanography, 1 (in Rus-
sian). Gidrometeoizdat, Leningrad.
Transl. Nat. Tech. Inf. Serv., Spring-
field, Va.
Lisitsyn, A. P.
1960 Recent sedimentation in the Bering
Sea. Israel Prog. Sci. Transl. Press,
Jerusalem.
Marshall, P. T.
1957 Primary production in the Arctic.
J. Conseil. 23:173-7.
772 Interaction of ice and biota
McRoy, C. P., and J. J. Goering
1974 The influence of ice on the primary
productivity of the Bering Sea.
In: Oceanography of the Bering
Sea, D. W. Hood and E. J. Kelley,
eds., 403-21. Inst. Mar. Sci., Occ.
Pub. No. 2, Univ. of Alaska, Fair-
banks.
Niebauer, H. J.
1980 Sea ice and temperature fluctuations
in the eastern Bering Sea and the
relationship to meteorological fluctua-
tions. J. Geophys. Res. (in press).
Saito, K., and A. Taniguchi
1978 Phytoplankton communities in the
Bering Sea and adjacent seas. Astarte
11:27-35.
Schumacher, J. D., T. H. Kinder, D. J. Pashinski,
and R. L. Chamell
1979 A structural front over the conti-
nental shelf of the eastern Bering Sea.
J. Phys. Oceanogr. 9:79-87.
Tabata, T.
1974
Movement and deformation of drift
ice as observed with sea ice radar.
In: Oceanography of the Bering Sea,
D. W. Hood and E. J. Kelley, eds.,
373-82. Inst. Mar. Sci., Occ. Pub.
No. 2, Univ. of Alaska, Fairbanks.
Walsh, J. J., T. E. Whitledge, F. W. Barvenik, C. D.
Wirick, and S. W. Howe
1978 Wind events and food chain dynamics
within the New York Bight. Limnol.
Oceanogr. 23:659-83.
i
The Role of Epontie Algal Communities
in Bering Sea Ice
V. Alexander and T. Chapman
Institute of Marine Science
University of Alaska
Fairbanks
ABSTRACT
The first significant primary production on the Bering Sea
shelf in spring takes place at the ice-seawater interface. The
extent, timing, and significance of this epontie production
were studied as part of the Bering Sea Outer Continental Shelf
Environmental Assessment study. Work was carried out by
UHIH helicopters and, in the course of ice-edge cruises, by
small boats and ship-based helicopters. The study primarily
involved measurements of chlorophyll and nutrients in ice,
but measurements of primary productivity and of the influ-
ence of light levels on primary productivity were also per-
formed. Results are compared with information on epontie
communities from elsewhere. Ice algae appear to be of quanti-
tative importance in the annual cycle, but their activity
actually represents a small proportion of the total, and their
primary significance in the ecosystem probably lies in pro-
viding organic material prior to primary production in the
water column.
INTRODUCTION
Each spring, the ice-seawater interface of annual
sea ice in the vast seasonal sea-ice zones of the world
serves as a growth substrate for an algal population
dominated by, but not exclusively composed of,
diatoms. This population is restricted to the bottom
few centimeters of ice, and precedes any substantial
growth of phytoplankton in the water below the ice.
Results of investigations in several areas have sug-
gested that this early spring ice-related growth could
account for a significant portion of the annual in-situ
photosynthetic carbon production in arctic waters
(Alexander 1974). Furthermore, its timing could be
critical to the grazing community, providing a food
source in a rather concentrated form before any
significant spring photosynthesis takes place in the
water column. Intuition leads us to assume that
from the point of view of ecosystem strategy, the
latter function might be the more important. Cer-
tainly, the evidence suggests that the epontie com-
munity cannot be ignored in a study of the
primary production regime of the southeastern Bering
Sea, and that its potential vulnerability to pollution
and the consequent implications for the ecosystem
could be dramatic. For example, a topic to be
developed further in this chapter is the role of the
ice community in providing food for fishes; a layer
of oil between the ice and seawater would clearly
be a problem.
The ice community is not easy to investigate. The
plant cells are generally adapted for low light (Clasby
et al. 1973), and experiments which involve bringing
a core of ice to the surface for photosynthetic meas-
urements are not feasible. Furthermore, because the
ice which contains the algae is often soft, it can be
lost as the core is retrieved. Clasby et al. (1973)
used a diving technique to carry out carbon-14
measurements of primary productivity under the ice,
with an in-situ method of injection and incubation of
samples. This work was done in the Chukchi Sea near
Point Barrow, and such techniques were practicable
at that nearshore permanent site, with a heated hut
on the ice and a permanent hole maintained for the
divers. In the Bering Sea, the work for the Outer
Continental Shelf Environmental Assessment Pro-
gram was done either from ships or helicopters, and
neither long-term in situ incubation nor the creation
of large holes for divers was possible. Consequently,
the effort was confined for the most part to chloro-
phyll measurements on samples collected with a
SIPRE corer, although some diving was done in the
looser ice near the edge in spring. The primary goals
773
174 Interaction of ice and biota
of our work were to determine the timing, intensity,
patchiness, and duration of the growth of ice algae
in order to assess the relative contribution of this
population to the Bering Sea ecosystem. The only
previously published observations for the Bering Sea
ice algal community were those of McRoy and
Goering (1974).
The occurrence of algae growing in sea ice has been
reported since the early 19th century, and such
populations appcEir to be important in both the
Arctic and Antarctic. A more thorough discussion
of the background was presented in Chapter 43,
and Horner (1976, 1977) presented a comprehen-
sive review of both the early steps and the recent
developments in our knowledge of ice algae.
The question of the quantitative importance of the
ice algae remains to be addressed; there is strong
evidence from other regions that this population
tends to be extremely patchy on both small and
large scales. We also need to know the role of the
ice algae in the ecosystem. George (1977) has de-
scribed a population of organisms which he terms
"under-the-ice benthos." Among the dominant or-
ganisms are amphipods adapted to live in association
with the under-ice surface, but the population also
contains heliozoans, hypotrichous ciliates, and
nematodes; and polychaete larvae and turbellarians
have sometimes been found. Likewise, Andriashev
(1968) called animals collected with an ice sampler
true ice animals, and included in this category poly-
chaetes, copepods, amphipods, and some fishes.
These animals are assumed to graze on the ice algae; it
is clear that, to some extent at least, the ice commun-
ity does serve as a source of relatively concentrated
food for grazing animals. There is further evidence
about how fish use the ice algae. Holmquist (1958)
mentions young sand lances (Ammodytes) hiding in
cavities in the ice. Arctic cod (Boreogadus saida) are
known to feed on crustaceans found on the underside
of ice floes; some of the characteristics of Boreo-
gadus may be considered adaptations to this inverse
benthos, since the oblique mouth opens forward and
upwards, while in the benthic cod genera such as
Gadus and Eliginus, the mouth is on the underside.
McAllister's (1975) list also includes Arctogadus
glacialis and Ammodytes hexapterus among the
ice-adapted fishes, and he deduced some conse-
quential food-chain involvements from the fact that
arctic char, birds, seals, and the beluga whale are all
sustained to some degree by the cryopelagic fishes.
Andriashev (1968) lists fry of the bottom-dweUing
nototheniid fishes, especially Trematomus borch-
greuinki, as primary feeders on the epontic algae in
the Antarctic.
Conflicting evidence exists concerning the possible
role of ice algae in seeding the planktonic component
as the ice melts. In the Chukchi Sea, Homer and
Alexander (1972) found that the ice algae sloughed
off from the ice and disappeared wdthout becoming a
noticeable component of the planktonic bloom below
the ice, and that furthermore the ice bloom and the
water bloom were separated in time. On the other
hand, Saito and Taniguchi (1978) suggested that in
the Bering and Chukchi seas, cells from the ice edge
form a significant portion of the plankton, and that
these ice-derived phytoplankton can be distinguished
in population structure and composition. Hameedi
(1978) came to a similar conclusion for the Chukchi
Sea. This question can be approached by studying
the timing of ice and water production, and by
observing the similarities and differences in species
composition of the populations.
A final question which has not been satisfactorily
answered to date is the fate of the organic material
produced in the ice. Clearly, some of it is disposed
of by grazing. However, an unknown proportion of
the material probably drifts dowm to the benthic
regions, where it may either be used immediately or
enter the detritus pool. Some of it may be made
available to plankton again later by wind resuspension
in shallow waters.
We were fortunate in our Bering Sea work in the
excellent logistic support available during the course
of the study. For example, we were able to use a
UHIH hehcopter based in Nome during an intensive
and extensive survey of ice algae distribution in
April of 1977. This enabled us to take samples from
the area of Norton Sound towards St. Lawrence
Island in the period of maximum epontic primary
production. Work near the ice edge was conducted
from the various ships of the NOAA fleet, with heli-
copter support from the Surveyor during part of the
work.
BERING SEA RESULTS
Regardless of the position of the ice edge, by the
time the ice-edge bloom begins, major production
by the epontic community has been in progress for
some time, and in fact is probably declining near the
ice margins. The ice-edge area, with chunks of soft
ice in the process of breaking up, does have a large
amount of brown coloration, and algae are also seen
in pools on the ice surface in clumps and strings
which appear to be distinct from the true epontic
community found under solid ice cover.
Eponlic algal communities 775
Helicopter survey
An intensive study was carried out to determine
the distribution of chloropliyll associated with sea
ice in an airea well to the north of the ice edge before
the beginning of ice melt. The work involved heli-
copter flights from Nome during the first week of
April, 1977, covering an area between 64°15'36"N
and 62°52'30"N in latitude and from 166°15'36"W
to 163°15'36"W in longitude. Thirty-one stations
were occupied within this area, and two sets of more
closely clustered stations were superimposed on this
broad survey grid to determine local variability
(Fig. 45-1). SIPRE ice cores were collected at each
station, and the lower portion was analyzed for
chlorophyll content, the length of the colored por-
tion of the core was recorded, and a surface sample of
seawater for nutrient determination was taken
through the hole created by the coring.
Chlorophyll content varied greatly among stations
(Table 45-1). For example, although high values
were found at one of the most southern stations
(96.8 mg/m^ chlorophyll a), one of the lowest values
was found in the same area at the same time (0.30
mg/m^ chlorophyll a). The chlorophyll content
ranged between 0.0 and 213.7 mg/m^ , with extreme
patchiness both on a general and on a local scale. A
concentrated area of browm ice at the northern end
of the study area had 0.5-30 cm of color within each
core, and under these circumstances as much as 64
mg chlorophyll a/m^ of sea surface was the maximum
concentration. Since a number of assumptions
must go into converting the volume measurements
into chlorophyll under a unit of sea surface, we
present the results in volume measurements. The
hazards of this are serious, since the algae occupy
only a small but variable portion of the lowest part
of the ice. As long as this is understood, the informa-
TABLE 45-1
Chlorophyll concentrations in northeastern
Bering Sea ice
170°
166°
162°
65°
SURVEY STATIONS
A ■ Intensive sampling locations
65"
64"
•46
ill
64°
•"
■ssjss:
^:":\v^^ '" .„ •:,
'"•„
■" J^iiisiliil
63°
'* **• "27
63"
170°
166"
162
Chlorophyll
Standard
Station
content (x)
deviation
Group
n
mg/m^
s
Range
All stations
63
23.1
40.9
0.0-213.7
Station cluster 1
18
12.0
17.6
0.0- 73.9
Station cluster 2
14
62.3
63.9
4.9- 85.1
(along edge of
shelf at entrance
to Norton Sound)
Figure 45-1. Map showing the station locations for the
April 1977 helicopter survey.
tion shown in Table 45-1 can be used for comparative
purposes.
The generally higher mean chlorophyll content
of the ice at the edge of the Norton Sound shelf
could be due either to timing of sampling or to
location. In any event, significant amounts of chlor-
ophyll a occurred in the ice in the area between
Norton Sound and St. Lawrence Island, extending
into the sound, during the first week in April. We do
not know how long this chlorophyll persists, and on
the basis of previous experience from the Beaufort
and Chukchi seas, we suppose that it could be present
and active for a period of about a month (Horner and
Alexander 1972, Clasby et al. 1976). The Bering Sea
chlorophyll maxima exceed those found in the
Chukchi Sea ice off Barrow, but are of the same order
of magnitude.
Nutrient analyses of water from under the ice
have shown that nitrate concentrations ranged from
2.5 to 8.6 [jigdit/\, ammonia from 1.4 to 4.7 /ug at/1,
phosphate from 0.8 to 1.7 jug at/1, and silicate from
12.1 to 42.1 A(gat/1.
More detailed coverage of the seasonal distribution
of ice algae in the Bering Sea would, of course, be
desirable, but it is not easily attainable. The logistic
problems and associated costs are likely to prohibit
long-term sampling. We have now obtained samples
from a wider area than had previously been covered.
Epontic algae near the ice edge
The questions of ice algal contribution to pelagic
open-water blooms and to ice-edge blooms and the
extent and duration of the grovd;h of algae within the
ice can be addressed by observations in the region of
the southern limit of ice during the early spring
period. Presumably, here the ice algae have grown
since the first moment when light was adequate,
and the first question is whether or not this grov^^h
776 Interaction of ice and biota
continues until breakup. In the true Arctic, growth
in the ice occurred well ahead of the maximum
growth in the water column, and the two production
periods appeared to be unrelated (Homer and Alex-
ander 1972). The conditions there, however, were
vastly different, and certainly did not represent, as
the area under study here does, a clear ice-edge
situation.
Our work at the ice edge has shown considerable
variation in the primary productivity and algal popu-
lations associated with ice. Three ice stations occu-
pied during the 1977 spring period from the Surveyor
showed high carbon assimilation rates, although the
nature of the ice and the algal populations was not
uniform. Pockets of dense algae occurred apparently
at random in disrupted, broken layers of sediment
and ice. Although quantitative information was not
obtained here, it is clear that this population has a
significant effect on the surrounding environment.
One way of measuring primary productivity in
the ice layer is to collect brash ice, which appears
reddish-brown in color because of living cells, to
allow it to melt at surface seawater temperature,
and then to carry out a carbon-14 primary produc-
tivity measurement on this material under surface
seawater light and temperature conditions. This
method yields results which approximate the activity
of cells released from the ice into surface seawater.
The results of one such experiment on material
collected from three stations are shown in Table
45-2.
Although this experiment does not approximate
normal dispersion of the cells into seawater, and
therefore presents an environment of unrealistically
low salinity for the cells, it does suggest a significant
influx of active cells into the seawater at the ice
edge. Counts of total cells in this material ranged
from 10' to lOVl-
An experiment in which photosynthesis of the
cells from ice station 3, Surveyor 5, was measured
at varying light levels in an incubator, using neutral
density screens to approximate light absorption by
water, showed that, among the light levels tested,
TABLE 45-2
Primary productivity and chlorophyll a in brash ice
Ice station
Primary productivity
mg/m^ /d
Chlorophyll a
mg/m^
2,SU5
3,SU5
1,SU6
295
396
208
4060
4060
3040
photosynthesis was greatest at the light intensity of
the surface, and was not inhibited in full daylight
(Fig. 45-2). This finding suggests that even though
most ice algae are considered low-light adapted, at the
Bering Sea ice edge by the time of ice breakup the
population is adapted to surface light and is capable
of colonizing the seawater environment at the ice
edge. Light measurements showed that less than
1 percent of the surface light penetrated 1 m of snow-
covered ice in the area, so that the region at the
bottom of the ice was certainly light-limiting for the
populations at this time.
Ice cores from the underside of solid ice floes were
also sampled successfully on one occasion. Four
replicates taken from within 1 m^ yielded a mean
primary productivity rate of 74 mg C/m^ /d. The
cores were incubated without thawing with approxi-
mately 30 ml of underlying water packed in ice and
100 percent of surface incident light on the upper
surface. About 6 percent of this radiation penetrated
the cores. Chlorophyll a concentrations were 30-50
mg/m^ . The level of activity is not inconsistent with
the light response curve for photosynthesis described
above. Interstitial nutrient concentrations appeared
to be adequate, so that light is probably the major
factor controlling primary productivity rates at
this time. Nutrient concentrations obtained from the
melted ice were: 7-22 /ug at/1 of NH3-N, 8-14 ^g
at/1 of NO3-N, 1-4 ^g at/1 of PO4-P, and 35-50 Mg
at/lof Si02-Si.
Although the difficulty in obtaining representative
samples and adequate coverage suggests that quantita-
tive significance should be assigned with caution,
our information attests to a significant role of ice
algae in the Bering Sea in initiating or at least con-
tributing to the ice-edge bloom. This supports the
Surface incident light
Figure 45-2. The relationship between primary produc-
tivity and light level as percentage of surface daylight for
ice algae from the Bering Sea ice edge.
Epontic algal communilies 777
suggestion by Hameedi (1978) and Saito and
Taniguchi (1978) with respect to the Bering and
Chukchi seas. Possibly this relationship in a true
marginal ice zone differs from that found in a sea-
sonal ice zone like those of the arctic coastal regions.
TABLE 45-4
*Comparison of ice algae and phytoplankton
identified from Discoverer Cruise 4, Station 6,
24 May 1977
Species composition of ice-edge and ice
communities of phytoplankton
X indicates that tiie taxon was found in that environment.
The phytoplankton living in
ice and slush ice
near the ice edge may contribute species to the
Water
water column, especially early in
the ice-edge bloom.
Taxon
Ice
column
In comparing species from nonq
samples with species found in t\
uantitativp ipp-mvp
le water
column at
the same location, we found considerable overlap
Achnanthes sp.
X
X
(Tables 45-3 and 45-4). For
example
, in Table
Amphiprora sp.
Asterionella japonica
X
X
45-3, Melosira sulcata is seen to
Dccur in
both types
A. kariana
X
X
of samples— this diatom was common in
both slush
Bacteriosira fragilis
X
ice and in the water column. 11
is not,
however, a
Biddulphia aurita
X
X
conspicuous member of all ice-ed
ge communities. In
Chaetoceros sp. cf. cinctus
X
C. compressus
X
TABLE 45-3
C. convolutus
C. deb His
X
X
^Comparison of slush -ice algae an
d phytopl
ankton
C. decipiens
X
identified from Surveyor Cruise 5, Station 9,
C. laciniosus
X
30 March 1977
C. radicans
C. socialis
X
X
X indicates that the taxon was found
in that en
vironment.
Chaetoceros sp.
X
X
Coscinodiscus sp.
X
X
Cylindrotheca closterium
Cylindrotheca sp.
X
Taxon Slush ice Water column
X
cf. Denticula sp.
cf. Detonub sp.
X
Actinoptychus undulatus
x
X
Amphiprora sp.
x
Ditylum brightwellii
X
Biddulphia aurita
x
X
Eucampia zoodiacus
X
Chaetoceros radicans
X
Gyrosigma or Pleurosigma sp.
XX
X
Chaetoceros spp.
x
X
Melosira sulcata
X
Coscinodiscus radiatus
X
Navicula pelagica
X
Cylindrotheca closterium
X
X
N. vanhoffeni
X
Gyrosigma or Pleurosigma spp.
X
X
Navicula sp.
X
Melosira sulcata
X
X
Nitzschia frigida
X
X
Navicula spp.
X
X
N. seriata
X
X
Nitzschia spp. (section Fragilariopsis)
X
X
Nitzschia sp. (section Fragilariopsis)
XX
X
Pleurosigma sp.
X
Porosira glacialis
X
Porosira glacialis
X
Stephanopyxis nipponica
X
Rhizosolenia hebelata
X
cf. Tabellaria sp.
X
Thalassionema nitzschioides
X
X
Thalassionema nitzschioides
X
X
Thalassiosira polychorda
X
Thalassiosira gravida
X
Thalassiosira sp.
X
X
T. nordenskioldii
X
unidentified pennates
X
X
T. polychorda
T. rotula
X
X
Peridinium spp.
X
Thalassiosira sp.
XX
X
dinoflagellates
X
Thalassio thrix frauenfeldii
X
Halosphaera
X
unidentified pennate diatoms
X
X
unidentified cells
X
Peridinium sp.
microflagellates
X
flagellates
XX
X
*from Schandelmeier and Alexander 1979.
*from Schandelmeier and Alexander 1979.
178 Interaction of ice and biota
the very early spring, ice flora may provide a signifi-
cant inoculum to the water column, but later in the
bloom the contribution becomes less important.
Comparison of species found at a station in June
shows that by then there was a much more diverse
population in the water column than in the ice,
although some of the same diatoms are present in
both environments. Although it is true that some of
the ice diatoms are motile littoral species and are not
well suited for a pelagic existence, we have also found
centric diatoms and chain-forming pennate diatoms in
the slush-ice samples and in some ice-core samples.
These organisms are common components of the
water-column phytoplankton.
Saito and Taniguchi (1978) have examined the
species composition of phytoplankton populations
in the Bering Strait and Chukchi Sea areas. These
authors have listed as ice plankton (defined as plank-
ton algae which have probably growTi in the ice):
Achnanthes taeniata Grunow, Fragilaria crotonensis
Kitton, F. islandica Grunow, F. striatula Lyngby,
Gyrosigma fasciola (Ehrenberg) Cleve, Navicula
directa (Wm. Smith) Cleve, N. distans (Wm. Smith)
Cleve, Nitzschia closterium (Ehrenburg) Wm. Smith,
N. cylindricus (Grunow) Hasle, N. frigida Grunow,
N. grunowii Hasle, Pleurosigma intermedium Wm.
Smith, P. normanii Ralfs.
This list does not overlap with the species found
at the active ice edge in the southeastern Bering Sea
to any significant degree. Saito and Taniguchi
(1978), in discussing their results from the Chukchi
Sea, described two stations at which large numbers
of diatoms were found, in one instance at a depth of
10 m (1.7 X lO'' cells/1) and in the other at a depth
of 30 m (1.6 X 10^ cells /I). The algae were domi-
nated by Nitzschia grunowii, recognized by these
authors as an ice species, and by Thalassiosira spp.
(considered a neritic pelagic form, part of the "spring
plankton"). The authors did not specifically suggest
that these populations were remnants of ice and ice-
edge spring blooms, but this seems likely in view of
the present information. Schandelmeier and
Alexander (1979) suggest that, at least in the south-
eastern Bering Sea, Thalassiosira spp. are a major
component both of ice communities and of ice-edge
blooms, contrary to the suggestion of Saito and
Taniguchi, who believe that these are non-ice vernal
bloom plankton.
DISCUSSION
We can now clearly address the first question
asked, that is, do the ice algae grow during the entire
period from the onset of adequate light until ice
breakup in the Bering Sea? The tentative answer
is yes, given the observation that active growth ap-
peared to occur both at the latitude of Norton
Sound and at the active ice edge in April of 1977.
This growth differs from that in the Chukchi Sea,
where the algae slough off from the ice before it
melts; but nutrient limitation may be the problem
there, whereas at the ice edge of the Bering Sea
nutrient depletion is less rapid and extreme. The
time sequence was described by McRoy and Goering
(1974). In February, they found no evidence for
algae in the sea ice; whereas in March they measured
a primary production rate of 44.40 mg C/m'' /d,
which can be converted to approximately 2.2 mg
C/m^ /d, assuming an algal layer 5 cm thick in the ice.
The chlorophyll concentrations associated with this
photosynthetic activity amounted to around 6.83
mg/m^ (0.34 mg chlorophyll a/m^ ). In April, they
measured chlorophyll concentrations averaging 59.49
mg/m^ (2.97 mg/m^ ), with an associated primary
productivity rate of 95.40 mg C/m-' /d. The data
from which this scenario is drawn were collected in
three different years for the three months, and
involved very limited sampling, but our more recent
data confirm this sequence. In the southernmost
portions of the sea ice, it is possible that two and a
half months (March, April, and part of May) of
active grovi^h occurs in the ice, whereas further
north it is unlikely that less than three months
(March, April, and May) of active growth occurs. The
interrelationship of ice algae and the ice bloom
further north on the Bering Sea shelf can to some
degree be deduced from the work of Saito and
Taniguchi, but no actual sampling has been done at
the retreating ice edge. Clearly, ice-related growth
and the ice-edge bloom in the southeastern Bering
Sea are closely interrelated.
Estimates for ice-edge production range from 2.2
mg C/m^/d (McRoy and Goering 1974) to 15 mg
C/m^ /d (three measurements presented above of
primary productivity in brash ice). Assuming a 100-
day period, this level of production would amount
to a total carbon contribution of 0.22-1.50 g C/m^/yr
by the ice algae. This amount, even inflated by a
generous estimate of the possible growing season,
does not appear to be of great quantitative signifi-
cance in the Bering Sea, but it is of the same order
of magnitude as the estimate for the coastal areas
of the Beaufort and Chukchi seas (Alexander 1974).
It may, in fact, be an underestimate, since often more
than 5 cm of brown ice is found within the ice cover.
It certainly represents less than 1 percent of the
annual primary productivity of the southeastern
region, and it may not be a major component of the
shallower shelf regions either. The ice community is
Epontic algal communilies 779
important primarily as a source of concentrated food
in tiie early season and of cells at the active ice edge.
During a late spring cruise of the R/V Alpha Helix
in the Bering and Chukchi seas in 1974, an attempt
was made to look at ice-related primary productivity.
Unfortunately, the ice had retreated well into the
Chukchi Sea and the ice edge was no longer actively
breaking up, but consisted of a large pressure ridge.
From the ice-edge region as a reference point, it soon
became obvious that very little chlorophyll was
present in surface waters, and the surface primary
productivity rates were extremely low. Looking at
the entire depth profile, we found phytoplankton
in the deeper waters between 30 and 40 m in the
near-ice area, and this was close to the bottom at
most stations. The population at this depth turned
out to be photosynthetically active, and later a sim-
ilar distribution of both phytoplankton chlorophyll
and productivity was found over large areas of the
shallow northeast Bering Sea. Integrating the depth
curves to obtain results per square meter of sea
surface produced fairly high daily productivity rates
(0.83 g C/m^ /d), much of this below the 1 percent
light-penetration depth. The possibility that this
deep photosynthetic activity is produced by cells
remaining from ice and ice-edge populations is
interesting; the early spring activity of pennate
diatoms could provide an inoculum for such summer
populations. This process leads to the question of the
role of ice algae in the benthic systems, either as a
direct food source or as detritus enhancing nutrient
supplies in the benthic environment. This question
cannot be answered yet, but the contribution of
carbon from ice eilgae, even if no grazing occurs, is
not large. The seeding mechanism discussed above,
coupled with resuspension by wind activity, is more
likely to be important. The high chlorophyll and
productivity in the deeper waters could very well be
related to enhanced nutrient supply near the sedi-
ment-seawater boundary. At any rate, the hypothesis
that incomplete grazing allows a significant portion of
the cell population in the ice and at the ice edge to
remain intact may be valid. These remaining cells
may contribute to a primary benthic system as well as
being a direct source of food.
The significance of nutrient availability for the ice
algae, especially the possible differences between
the Bering Sea and the Chukchi Sea, deserves more
attention here. Clasby et al. (1973) found that
in the coastal area near Barrow, interstitial levels of
nitrate and ammonia both declined during the spring
ice-algae pulse, and nutrient depletion may have
been involved in the population decline after the
peak. Tracer studies showed that both nitrate and
ammonia were used by the population. In the
Bering Sea, ammonia levels within the ice were higher
than in the underlying water (7-22 ng at /I in ice,
and less than 1.0 /jg at/1 in water) before algal growth.
This ready source of nitrogen could be important to
ice algae at the low energy -limiting light levels. Some
in-situ regeneration of nitrogen as ammonia is likely
within the ice as the ice community develops, and
this source could be important in sustaining grovi1;h,
along with the contribution from the seawater
below. By the time Bering Sea ice-edge algae are
discharged into the seawater at the ice edge, there is
enough light to allow survival, grovvi;h, and assimila-
tion of nitrate, which is relatively abundant in the
seawater. In the Chukchi Sea, nutrient limitation and
sloughing off of the cells occurs before there is
enough light in the water column for the cells to
survive.*
REFERENCES
Alexander, V.
1974 Primary productivity regimes of the
nearshore Beaufort Sea, with refer-
ence to the potential role of ice
biota. In: The coast and shelf of the
Beaufort Sea, J. C. Reed and J. E.
Sater, eds., 609-35. Arctic Inst. N.
Amer., Arlington, Va.
Andriashev, A. P.
1968 The problem of the live community
associated with the antcirctic fast
ice. In: Symposium on antarctic
oceanography, R. I. Currie, ed.,
147-55. Scott Polar Res. Inst.,
Cambridge, England.
Clasby, R. C, V. Alexander, and R. Homer
1976 Primary productivity of sea-ice algae.
In: Assessment of the marine environ-
ment: Selected topics. D. W. Hood,
ed., 283-304. Inst. Mar. Sci., Occ.
Pub. No. 4, Univ. of Alaska, Fair-
banks.
Clasby, R. C, R. Horner, and V. Alexander
1973 An in situ method for measuring
primary productivity of sea-ice algae.
J. Fish. Res. Bd. Can. 30:835-8.
♦Contribution No. 422, Institute of Marine Science. University of
Alaska, Fairbanks.
780 Interaction of ice and biota
George, R. Y.
1977
Dissimilar and similar trends in ant-
arctic and arctic marine benthos.
In: Polar oceans, M. J. Dunbar, ed.,
391-408. Arctic Inst. N. Amer., Cal-
gary, Alberta, Can.
Hameedi, M. J.
1978 Aspects of water column primary
productivity in the Chukchi Sea
during summer. Mar. Biol. 48:37-46.
Holmquist, C.
1958
An observation on young Ammodytes
dubius. Danish Biol. Sta., Disko
Island 23:10-14
Homer, R., and V. Alexander
1972 Algal populations in arctic sea-ice:
An investigation of heterotrophy.
Limnol. Oceanogr. 17:454-8.
McAllister, D. E.
1975 Ecology of the marine fishes of arc-
tic Canada. In: Circumpolar con-
ference on northern ecology, II:
49-65. Nat. Res. Council of Canada.
McRoy, C. P., and J. J. Goering
1974 The influence of ice on the primary
productivity of the Bering Sea.
In: Oceanography of the Bering
Sea, D. W. Hood and E. J. KeUey,
eds., 403-21. Inst. Mar. Sci., Occ.
Pub. No. 2, Univ. of Alaska, Fair-
banks.
Horner, R. A.
1976 Sea-ice organisms. Oceanogr. Mar.
Biol. Ann. Rev. 14:109-82.
Saito, K., and A. Teiniguchi
1978 Phy to plankton communities in the
Bering Sea and adjacent seas. As-
tarte 11:27-35.
1977 History and recent advances in the
study of ice biota. In: Polar oceans,
M. J. Dunbar, ed., 269-84. Arctic
Inst. N. Amer., Calgary, Alberta,
Can.
Schandelmeier, L., and V. Alexander
1979 A quantitative study of the phyto-
plankton from the eastern Bering
Sea. In: Primary productivity,
nutrient cycling and organic matter
transfer. Final Rep. to NOAA.
Ice as Marine Mammal Habitat
in the Bering Sea
John J. Burns,' Lewis H. Shapiro,^ and Francis H. Fay^
' Alaska Department of Fish and Game
Fairbanks
^ University of Alaska
Fairbanks
ABSTRACT
Annually recurring features of the ice sheet in the Bering
Sea exhibit a high degree of organization. An array of differ-
ent ice habitats, used by ice-associated marine mammals,
results from interaction of broadly repetitive, seasonally
prevailing weather and oceanographic conditions which occur
within the physical boundaries and around physical features of
the continental shelf. The greatest habitat differentiation of
the annual ice cover is concurrent with establishment and
duration of annual steady-state maximum ice conditions.
These involve ice formation (mainly in the north), southward
transport toward the shelf break, and disintegration near it.
Physical constrictions and barriers to ice movement, together
with regionally different wind and ocean current regimes,
produce the different habitats, which are spatially and tempo-
rally repetitive and predictable. Ecological strategies (and
habitat requirements) of the eight ice-associated marine
mammals result in their nonrandom distribution. During
maximum annual ice extent, spotted (Phoca largha) and
ribbon (P. fasciata) seals occur in the ice front and ringed
seals (P. hispida) mainly in landfast and heavy pack ice.
These three species depend on some degree of ice stability for
successful rearing of their young. The birth period for each
occurs during the last stages of steady-state ice conditions.
Walruses (Odobenus rosmarus) and bearded seals (Erignathus
barbatus) occur largely in the main pack. The distribution of
walruses is highly clumped, with two and sometimes three
major areas of concentration in winter and early spring in and
adjacent to regions of persistent polynyas and ice divergence.
Bearded seals are widely distributed throughout the pack in all
regions of persistent ice motion and divergence; the greatest
abundance is in the central Bering Sea. Young of both walrus
and bearded seals can swim at birth, and the peak period of
births occurs when the pack begins its seasonal disintegration
and northward retreat.
Benefits of ice to bowhead (Balaena my slice tus) and beluga
(Delphinapterus leucas) whales are not clear. Bowheads are
probably most abundant in the western Bering Sea in late
winter, primarily in the more open, labile parts of the pack,
including the front and areas near St. Matthew and St. Law-
rence islands. Belugas are more widely distributed, occurring
in all regions where leads and openings, including relatively
small ones, are continuously formed. Bowheads bear calves
from May to July, in ice-covered waters mainly north of the
Bering Sea. Belugas calve mainly in July, in ice-free coastal
waters.
Polar bears (Ursus maritimus) occur in the northern Bering
Sea mainly from January through March. They are associated
with the thicker, more extensive pack and their abundance
there varies annually. It is thought that there are few pregnant
females in the Bering; for most bears, this region is a periph-
eral part of their range in which they move and feed according
to the annual extent of favorable habitat and prey abundance.
INTRODUCTION
Ice is a major component of the physical environ-
ment of far northern marine systems. In the Bering
Sea it occurs annually from November through
June. The characteristics of the dynamic, seasonal ice
cover exhibit great temporal and spatial variation, but
it changes in an orderly and predictable manner.
Early aboriginal as well as contemporary subsistence
hunters have long recognized the general relationships
between ice conditions and the distribution and
movements of animals. In recent years ecologists
have begun to investigate these relationships in
greater detail. Scientists concerned with ice have also
increasingly begun to turn their attention from the
multiyear ice of the Polar Basin to the seasonal pack,
which is important to annual events (biological and
physical) in regions at lower latitudes, including the
Bering Sea. Oceanographers have continued to
increase and refine our understanding of this region.
Recent technological advances, together with
intensified research efforts in marine systems of the
north, are producing a rapidly increasing data base.
During the 1950's and 1960 's, those of us engaged in
marine mammal research in the Bering Sea obtained
most of our data in the immediate vicinity of Eskimo
villages during the course of daily forays in small
boats or afoot. Those efforts were infrequently
augmented by an occasional expedition on ice-
strengthened vessels and by aerial surveys. Collective-
ly, we were able to record ice conditions and to
document the distribution and relative abundance of
different mammals within very limited geographic
areas over rather long periods of time. Intuitive
reasoning and increasing understanding of ecological
strategies of the different marine mammals suggested
the kind of ecological partitioning that might occur
and the diversity of ice habitats that might exist over
broader areas.
781
782 Interaction of ice and biota
On the basis of a combination of information from
Eskimo hunters, data from studies conducted at
major coastal hunting sites, and data acquired from
aerial surveys, ship expeditions, and reports of Soviet
sealers. Bums (1970) compiled the first broad over-
view of the distribution and movements of ice-
associated marine mammals in the Bering and Chukchi
seas. Fay (1974) considerably expanded our under-
standing of how^ and why these mammals make use of
ice and of the dynamics of the seasonal ice sheet. His
summary represented the state of knowledge as of the
winter of 1971-72.
The availability of high-resolution satellite imagery
dramatically increased the data base required to study
large-scale movements and major features of seasonal
ice and, in combination with other data, the charac-
teristics of marine mammal habitats within the
extensive pack. Imagery from Earth Resource
Technology Satellites (ERTS, later called LANDSAT)
became available in 1972. Other satellite systems
which provided repetitive, broad-scale synoptic
imagery included DAPP (in 1972) and NOAA/VHRR
(in 1974). The advent of huge volumes of satellite
imagery gave impetus to several studies of ice dynam-
ics in waters adjacent to Alaska.
These studies, combined with those on the biology
and oceanography of the region, added important
information required for understanding the role of ice
in the ecological strategies of those marine mammals
which depend on its presence for the successful
completion of major biological functions. Detailed
studies of the relationships of marine mammal
distributions, densities, and activities to sea-ice
conditions have been conducted under the aegis of
the Bureau of Land Management/Outer Continental
Shelf Environmental Assessment Program (BLM/
OCSEAP) since 1975 (summarized by Braham et al.,
in preparation, and Bums et al. 1980). The current
status of OCS-related studies is indicated by the
number of unpublished manuscripts cited in this
chapter.
This chapter is intended as a summary of our
current understanding of factors which produce
different features of the seasonal ice cover and a
synopsis of the marine mammals which occupy
the resulting set of habitats. The information is
drawn primarily from recently completed studies of
Bums et al. (1980).
FACTORS AFFECTING DEVELOPMENT
OF ICE HABITATS
The physiography, oceanography, and climate of
the Bering Sea region interact to produce a seasonal
ice sheet which has a high degree of organization.
Annual differences in extent, thickness, and other
features of this sheet are directly related to smaller
scale annual variations in oceanographic conditions
(mainly currents and sea temperature) and weather
(mainly air temperature and surface winds).
The Bering Sea is a well-defined body of water
almost completely surrounded by land. There are
several dominating physiographic features. It is
divided into two approximately equal parts— the shelf
region of the northern and eastern half, where water
depths are less than 200 m, and the deep southwest-
ern half. Since ice is restricted to the shelf, every
year it covers up to half of the Bering Sea. The sea is
narrow in its northern part and progressively wider
southward.
Shoreline configuration, constrictions such as
Anadyr and Bering straits, and several large islands all
influence features of the ice sheet. These influences
vary in relation to seasonally prevailing weather and
oceanographic events. In a broad sense, these physio-
graphic features constitute a fixed mold within which
the ice sheet develops, is transported, and disinte-
grates in response to the other causative factors.
The deep Bering Sea (>200 m) is of significance
because waters of this region are a major reservoir of
heat over which ice cannot persist. Muench and
Ahlnais (1976) suggest that in the central Bering Sea
the relatively warm Bering Slope current which flows
northwest parallel to the shelf break (Kinder et al.
1975) controls the annual southern limit of ice.
Both studies suggest that in western Bristol Bay the
southern ice limit is similarly controlled by circula-
tion paralleling a shallow (50 m) scarp-like feature.
In the same way, the deeper warm-water boundary
limits ice advance because of rapid melting. The great
expanse of open water along the southern ice fringe
also significantly shapes features of the adjacent ice
cover. Wave action near the ice terminus penetrates
the ice sheet, fracturing it into uniformly small floes
(Bumsetal. 1980).
The intensity of generally northward-setting
currents on the shelf (strongly influenced by those of
the deep Bering) varies according to season: the
currents are weaker during the period from autumn
to early spring (Coachman and Aagaard, Chapter 7,
Volume 1; Kinder and Schumacher, Chapter 5,
Volume 1; Muench et al., Chapter 6, Volume 1).
During this time flow of warm water to and across
the shelf is generally reduced. Episodes of flow
reversal are known to occur and are more frequent
and of longer duration during autumn and winter
(Bloom 1964, Coachman and Aagaard, Chapter 7,
Volume 1). These reversals, although perhaps insignif-
i
Ice as marine mammal habitat 783
icant in total water transport, facilitate rapid south-
ward transport of ice, particularly through the Bering
Strait. The frequency and duration of reversals will
probably be found to vary annually according to the
major components of annually different weather
cycles (particularly pressure systems). Shallow
depths on the shelf facilitate thermohaline convection
and therefore promote a vertically uniform water
column (Muench and Ahlnas 1976), which, during
the cold seasons, facilitates the development and
persistence of ice.
Initial formation of ice depends on air and surface
water temperatures. As Muench and Ahlnas (1976)
indicate, subsequent motion is controlled primarily
by wind and water currents. Weather patterns over
the northern Bering Sea include prevailing southerly
winds during the summer, variable vdnds during the
late spring and early autumn, and prevailing northerly
(usually northeasterly) winds from late autumn
through early spring (Fay 1974; Burns, personal
observation). Surface winds strongly influence sea-
surface currents and the direction and rate of drift of
ice.
Usually, air temperatures low enough to freeze sea
water occur in the northern Bering from mid-October
through about late April. However, sea-surface
temperatures are not sufficiently lowered until
mid-November to early December; they remain low
into May. Although most of the ice in the Bering Sea
forms in the north, there is an annually variable influx
from the Chukchi Sea through the Bering Strait (Fay
1974; Shapiro and Burns 1975a, 1975b; Muench and
Ahlnas 1976). Since the formation and presence of
ice intensifies water cooling, once the process begins,
it proceeds at an increasing rate (further expedited by
the progressively lowering air temperatures of late
autumn and vvdnter). The ice sheet subsequently
tends to modify weather (Konishi and Saito 1974,
Okawal974).
DEVELOPMENT OF ICE HABITATS
Initial formation of pack ice in the northern Bering
Sea usually involves some influx of ice from the
Chukchi Sea through the Bering Strait, but most of
the shorefast and pack ice forms in the Bering.
Weather patterns during the annual ice cycle deter-
mine the extent of ice contribution from the
Chukchi.
There are examples of cold and warm autumns
(early and late initiation of ice development). In
October and November 1979, strong, persistent
northerly winds in the Chukchi and northern Bering
drove the pack southward to the vicinity of Little
Diomede Island (Bering Strait) on 19 November and
St. Lawrence Island on 25 November, before there
was any appreciable local formation of ice.
With weather conditions similar to those which
occurred in November 1979, transport of ice south-
ward through Bering Strait begins earlier than usual
and presumably involves a mass of ice greater than
normal transported at higher than average rates for
longer sustained periods of time. Formation of
the ice sheet is intensified through feedback relation-
ships as winter progresses (Konishi and Saito 1974).
Higher than normal rates of ice influx and formation
continue when the early cold winter weather patterns
persist. Frequently they do not, however.
During some years the reverse conditions occur:
southerly air flow persists well into, or even through-
out, the winter. Associated with this southerly flow
are air temperatures warmer than normal, frequent
storms, currents from the south presumably stronger
than normal, and warmer water temperatures. Such
conditions prevailed in the winter of 1966-67. Resi-
dents of Little Diomede Island during that winter
reported that the "arctic" ice did not appear in
Bering Strait until early March and began to recede
northward by early April. The ice sheet did not begin
to form until late December. It was limited through-
out the entire winter, and observations made during
aerial surveys of marine mammals in April and May
indicated that it was probably almost completely
composed of ice formed in the Bering Sea.
These conditions, representing deviations from a
norm (which itself shows significant Vciriation), aire
the initial stages of either an extensive or a limited ice
year. The maximum extent of ice, which may be
attained in February but occurs more commonly in
the period from March to April (Wittmann and
MacDowell 1964, Fay 1974), depends on the cumula-
tive effects of weather and oceanographic conditions
throughout the period of ice development. During
this time weather in the Bering Sea region may be
dominated consistently by arctic high-pressure
systems, which favor ice formation and transport
southward. Or it may be variable, regionally differ-
ent, or dominated by northward displacement of the
North Pacific lows, which limit ice formation and
transport. Konishi and Saito (1974) indicate that
weather conditions and sea currents in the Bering Sea
occur in cycles of two years. The southern limit of
the pack in March and April since 1960 is shown in
Fig. 46-1. It is the array of different habitats within
the seasonal ice sheet which is important to the
different marine mammals.
Fast ice (referred to in the local vernacular as
"shore ice") is one of the leeist dynamic habitats. It
develops along the shores of all the larger islands of
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Ice as marine mammal habitat 785
the central and northern Bering Sea as well as along
the mainland shores from 56° or 57° N latitude to the
Bering Strait. In the southern parts of the Bering it is
frequently short-lived, occurring only during periods
of extreme cold. In the central and northern Bering
it persists from December to late May or early June,
usually attaining its maximum extent in April. It
varies in width from a few meters to several kilo-
meters, depending on both latitude (weather) and
configuration of the coastline (exposure to prevailing
winds and ocean currents). It is most extensive where
it is protected by some physiographic feature from
strong winds, currents, and the drifting pack. In
some parts of the Bering these same forces drive thick
ice into shallows, where it becomes grounded and
serves to protect and stabilize the thinner, floating
fast ice surrounding grounded floes. However, the
latter process is more important in the Chukchi and
Beaufort seas. Embayments such as the numerous
fjords of the eastern Chukotsk Peninsula, as well as
Norton Bay, Golovnin Bay, Port Clarence, and
Grantly Harbor, are protected areas in which an
extensive, continuous, relatively flat cover of floating
ice develops and remains in place until late spring.
Unprotected shorelines such as eastern and western
St. Lav\rrence Island, King and Diomede islands, and
exposed capes accumulate little persistent fast ice.
Fast ice develops along the remaining shoreline to a
greater extent, depending on weather and interaction
with the pack.
The pack, by definition in constant motion, is
highly dynamic and geographically variable. From
the onset of freezing conditions its net transport is
southward, driven by prevailing northeasterly vdnds
and probably intensified by current reversals.
Southward drift is slowed or reversed by episodes of
light variable or southerly wind. Fig. 46-2 shows the
direction and extent of movement of individually
recognizable floes in the Bering Strait region during a
period of strong northerly winds (currents unknown)
on 6 and 7 March 1973 (Shapiro and Burns 1975b).
Southward trajectories of recognizable floes in the
central Bering during March and April 1974 were
shown by Muench and Ahlnas (1976).
Although net transport of ice is southward from
November-December until about mid- to late April,
the rate and direction of drift are not uniform
throughout the pack. Local winds, regionally differ-
ent current regimes, constrictions, barriers, and lee
shores all contribute to a geographically different but
generally repetitive array of ice conditions. The pack
is mostly compressed against north-facing shores and
is driven away from south-facing ones. For example,
at St. Lawrence Island, during northerly winds ice
forms an extensive mass of compressed floes on the
north side and is deflected around the east and we.st
ends of the island, through narrower areas where
compression is considerable. On the south side ice is
continuously driven away from the island; a large area
of open water or thin, rapidly forming ice remains.
Similar conditions are produced in the Gulf of
Anadyr, Norton Sound (particularly the eastern part).
50 km
Figure 46-2. Displacement vectors of individual ice floes
in the Bering Strait region for the interval March 6-7,
1973. Scale of vectors is indicated on map. Dotted lines
indicate seaward margin of fast ice (from Shapiro and
Burns 1975b, Fig. 3, p. 382).
786 Interaction of ice and biota
Nunivak Island, St. Matthew Island, Bristol Bay, and,
to a lesser extent, along other less extensive south-
facing shores. Compression, deflected flow, and
persistent polynya systems are illustrated in Fig. 46-3.
As Shapiro and Burns indicated (1975a), drift is
not continuous to the south. However, episodes of
northward drift seldom occur during winter and early
spring. When they do, ice displacement tends to be
small, geographically limited, and of short duration,
because of the presence of the extensive pack in the
more restricted northern Bering. Satellite imagery for
periods of clear weather showed the frequency of
directional drift to be 10 percent northerly, 50
percent southerly, and 40 percent no detectable
movement. Clear weather conditions prevail from
February to early April.
The importance of the areas of open water as
centers of rapid ice growth was suggested by Badgley
(1966), who found that heat loss through ice was one
or two orders of magnitude less than through open
water. Personal observations of "sea smoke" over
open and recently refrozen leads indicate that the
rate of heat loss probably differs according to the
thickness of the ice and the amount of accumulated
snow cover. Muench and Ahlnas (1976) recog-
nized the importance of the extensive open-water/
thin-ice areas as sites of rapid growth of ice which
augmented the southward-drifting pack. During
moderate winds, leads and polynyas may appear
virtually ice-free, with ice crystals in turbulent surface
waters to a depth of more than 2 m (Burns, personal
observation). When winds diminish, a relatively
thick layer of ice is rapidly formed as the crystals
consolidate near the surface.
The ice sheet undergoes significant consolidation
and deformation in its progress through areas of high
compression. Thus, the streams of floes emerging
southward through the Bering Strait or around the
east and west ends of St. Lawrence Island include
some of the most heavily ridged and deeply keeled ice
in the seasonal pack (Burns et al. 1980). After
emerging from the regions where the greatest defor-
mation occurs, they continue to drift southward into
the wider parts of the Bering Sea, where there are
Figure 46-3. Synoptic view of tiie ice cover in the Bering Sea during an episode of southward movement. Note areas of
open water and thin ice south of St. Lawrence Island and the northern parts of Norton Sound and the Gulf of Anadyr.
NOAA/VHRR satellite image 6526, 19 April 1976.
Ice as marine mammal hahllat 787
few barriers to movement. According to floe trajec-
tories shown by Muench and Ahlnas (1976), ice in
the vicinity of St. Lawrence Island could reach the
southern limit of the pack in 30-45 days.
The southern parts of the pack are subject to
continuous melting and periodic disintegration
because of warmer sea-surface temperatures and wave
action. These forces produce two zones of variable
width, referred to as the fringe and the front. The
fringe is the narrow, irregular southern margin of the
pack, composed of tongues of wind-rafted, broken,
melting ice, which directly receives the first impact of
surface chop and waves from the open sea. The front
is a broader zone, strongly affected by waves which,
depending on conditions, are known to penetrate the
pack as deeply as 133 km (Bums et al. 1980). It is
the transition zone between the rapidly disintegrating
fringe and the heavier, southward-drifting pack. The
process of physical breakup caused by wave action is
the major force affecting the size of floes in the front.
The front can be considered a zone of dynamic
equilibrium between regions sufficiently cold to
produce and maintain ice and those where melt
is rapid. As Muench and Ahlnas state (1976), under
regional nearly steady conditions, like those existing
mainly in March through April,
the ice regime can be thought of as consisting of a
northern source region, an intermediate region of
southward ice advection, and a southern area of ice
disintegration.
During cold winters the northern source region
extends considerably farther south, rapidly producing
new ice in any openings formed in the drifting pack.
The front is the beginning of the region of ice disinte-
gration; the fringe represents the final stage of that
process.
The fringe and the front, during the steady-state
seasonal ice maximum, approach or overlie the shelf
break and extend completely across the Bering Sea.
Together these zones are the most labile segments
of the winter pack (Burns et al. 1980). They are
rapidly dispersed (southward) or compacted (north-
ward) by appropriate winds, and their combined
width (from fringe to heavy pack) has been observed
to vary from 30 km to more than 140 km (Fig. 46-4).
The size of floes in the front is relatively uniform,
except in Bristol Bay. In this region the ice is pre-
dominantly thin, rafted, relatively flat, and composed
of angular floes mostly more than 100 m in diam-
eter. Farther west, adjacent to deeper and more
expansive open water, they are uniformly small,
usually less than 20 m in diameter, and usually
separated by water, slush ice, and brash. Occasion-
ally, during brief periods of calm, this ice re freezes
Figure 46-4. ERTS image of the ice fringe and front zone
in central Bering Sea. St. Paul (lower center) and St.
George (lower left) islands are visible. ERTS image 2453-
21445-7,19 April 1976.
into a consolidated unit. During or just after each
storm (reinitiation of wave action), the consolidated
front is again broken up into small floes. The uni-
formity of floe size north of the fringe suggests some
unknown structural characteristics of the ice itself or
of waves dampened by their first encounters with ice
of the narrow fringe zone.
Beyond Bristol Bay, floe size tends to be uniform
from east to west within the front, although the
thickness and extent of deformation are different.
Thickness and deformation increase westward,
indicating the increased incorporation into the front
of ice from more northern areas of the Bering Sea. In
the regions south of Nunivak Island and in Bristol
Bay, the front is not far removed from the place
where ice is formed and little deformation occurs
during transport.
USE OF ICE HABITATS BY
MARINE MAMMALS
More than 25 species of marine mammals occur, to
some extent, in the continental shelf waters of the
Bering (Fay 1974). They cope, in one way or anoth-
er, with four phases (seasons) of the annual ice cycle,
the intensity and duration of which are annually
somewhat variable. These phases include: ice-free
788 Interaction of ice and biota
conditions with attendant "warm" water (July
through October); development of the ice sheet,
including its intensifying formation, expansion
southward, and increasing area of cold water temper-
atures (the transition phase from November through
January); the steady-state seasonal maximum ice
cover and cold water (February or March through
mid-April); and the transitional decay and northward
retreat of ice with rising temperatures (mid- to
late April through June).
Eight marine mammal species use the pack to
advantage over a prolonged time and depend on its
presence at least from March to May or June. These
include two cetaceans, the bowhead whale (Balaena
mysticetus) and beluga whale (Delphinapterus
leucas); five pinnipeds, walrus (Odobenus rosmarus),
ringed seal (Phoca hispida), spotted seal (Phoca
largha), ribbon seal (Phoca fasciata), and bearded seal
(Erignathus barbatus); and one fissiped, the polar
bear (Ursus maritimus). The arctic fox (Alopex
lagopus) occurs on some parts of the pack but in this
discussion is not considered a marine mammal. Other
strongly ice-associated species such as the narwhal
(Monodon monocerus), the hooded seal (Cystophora
cristata), and the harp seal (Phoca groenlandica),
known in local folklore of the northern Bering region,
are considered to be extralimital wanderers from the
North Atlantic regions.
In the Bering Sea, the range of the ice-associated
pinnipeds and cetaceans under discussion mostly
coincides with that of the seasonal pack, although
some animals of each species may, to a greater or
lesser extent, remain during the ice-free periods. The
range of the polar bear is largely restricted to the
northern parts of the winter pack.
Fay (1974) summarized the functions which ice
serves for the pinnipeds: it constitutes a solid sub-
strate on which they can rest, bear and care for their
young, mate, and molt. For the polar bear also,
ice serves these functions, although most births
occur on land (Harington 1968, Lentfer 1972).
It is not known what functions ice serves for bow-
head and beluga whales.
Advantages of the seasonal ice to those marine
mammals successfully adapted to use it include
isolation from terrestrial predators and disturbances;
vastly greater space within which to distribute them-
selves for feeding, resting, and other functions;
variety in the form of a diversity of habitats; close
proximity to food supply, which is either directly
beneath the ice, or, for polar beairs, abundant and
accessible in an extensive area; passive transportation
with the pack to new feeding areas or in the course of
seasonal migrations; favorable sanitation resulting
from the increased space, reduced competition for
hauling sites, and cleansing through additions of
snow, growth of new ice, and regional or seasonal
disintegration of older ice; and availability of shelter
in the form of naturally occurring ridges and cavities
or accumulated snow (Fay 1974). The pack also
provides shelter by creating a microclimate in which
surface winds are greatly reduced, and wave action is
dampened or eliminated in the shelf waters occupied
by the marine mammals.
Each of the eight species of marine mammals under
discussion exploits a different ecological niche within
the pack and thus the mammals tend to partition
their environment. Such partitioning in the Bering
has been recognized and is discussed by Burns (1970),
Fay (1974), Braham et al. (in preparation), and Burns
et al. (1980). Mammals need regular access to air.
Ice is a barrier between water and air, and presents
different problems to the different species. These
problems may be largely negligible to bears, which
roam the pack, or major to beluga v/hales, which can
become trapped in isolated openings or perish in an
unbroken cover of relatively thin ice through which
they cannot surface (Kleinenberg et al. 1964). It
is obvious that each of the pinniped species occupies
regions where it can physically cope with prevailing
ice conditions, where it can obtain adequate and
appropriate food, and where its requirements for a
suitable ice substrate necessary for performance of
important events in its life cycle are repeatedly and
dependably available at the appropriate times.
In general terms the pack ice can be divided into
several kinds of mammal habitats, including fast ice,
the fringe, the front, and the main pack. During the
course of its formation and transport, the pack occurs
in or passes through regions where it is strongly
compressed and the cover is complete, where it is
continuously dispersed and has many continuously
developing leads and other openings, and where it is
moved away from east-west oriented shores next to
which persistent and sometimes connecting systems
of polynyas occur.
During the initial autumn and early winter condi-
tions of transition from open water to extensive ice
cover, few associations of marine mammals with
specific ice conditions are evident. Walruses, beluga
and bowhead whales, and ringed, bearded, and
spotted seals disperse into the Bering Sea a little
before and with the advancing ice cover, or leave the
coastal zone to meet the advancing pack as it forms.
Polar bears move into the northern Bering Sea in
association with incursions of heavy ice from the
Chukchi, mainly during January and February in
most years. The southward migration of ringed
Ice as marine mammal habitat 789
seals through Bering Strait continues for a long
time, extending at least through February.
Ribbon seals are thought to remain mainly in the
Bering Sea during the open-water seasons and to
associate with the ice as it approaches the central
and southern parts of the shelf. Little selection for
specific ice types exists in autumn and early winter;
indeed the ice sheet is not much differentiated.
Progressive growth and expansion of the seasonal
ice produces progressive differentiation of the various
ice habitats until the annual steady-state condition is
attained. By February the marine mammals have
distributed themselves in their preferred (or re-
quired?) habitats and the maximum partitioning
becomes evident. This partitioning prevails, depend-
ing on the species, as late as June.
Ringed seals
Ringed seals can be found throughout the Bering
Sea pack, but they occur in greatest densities in the
fast ice; they are the only pinniped species which can
effectively utilize this habitat for long periods. Fast
ice provides optimal conditions for constructing birth
lairs (mainly in drifted snow) in which pups are bom
and nursed (McLaren 1958, Burns 1970, Smith and
Stirling 1975), and in the Bering it is the habitat in
which most adults mate, breed, and molt. Within the
pack they are most abundant in the heavy ice of the
northern Bering Sea (they are even more abundant in
the Chukchi), and are rarely encountered in the very
labile ice of the front and fringe. In the Bering Sea
pups are born mainly in early April, when the ice
extent, including that of fast ice, is at its maximum.
Pups are nursed for approximately four to six weeks,
during which time they continue to use the birth lair,
as long as it remains intact. Weaning is abrupt,
occurring when the birth lair is destroyed (sometimes
prematurely), or when the mother departs. Ringed
seals in the consolidated, heavy pack and the fast ice
of the extreme northern Bering Sea are subject to
predation by polar bears; the pups are preyed upon
also by arctic foxes.
Spotted and ribbon seals
Spotted and ribbon seals occur almost exclusively
in the front and fringe, extending the entire breadth
of the Bering Sea. Spotted seals are most abundant
in the southern parts of the front (extending into the
fringe) with centers of abundance in western Bristol
Bay, near the Pribilof Islands, and in Karaginsky Bay
(Braham et al. in preparation). Ribbon seals are most
numerous in the northern parts of the front wdth
centers of abundance in the central and western
Bering Sea. In both species births occur from late
March through late April, most in the first 15 days of
April. Pups are bom exposed on the ice floes, as
"whitecoats." They use irregularities of the ice
surface for protection from winds. At three to four
weeks of age, by which time the white lanugo is
usually shed, weaning occurs; it is abrupt and pups
are left to fend for themselves. Since the front is
south of the consolidated pack, it is almost devoid
of polar bears and arctic foxes.
Bearded seals
Bearded seals are the most generally distributed
seals within the seasonal ice sheet, excluded only
from fast ice and regions of continuous ice compres-
sion. They occur wherever ice overlies waters shallow
enough for bottom feeding (<150 m) and where it
tends to disperse and openings are continuously
formed. Although widely distributed, they are most
abundant in the central parts of the seasonal ice.
They are reported to make breathing holes through
relatively thick ice in the far north (Stirling and
Smith 1977) but seem to do so seldom in the Bering.
However, they commonly break through thin ice by
pushing upwards with their heads. Pups are born
from March through mid-May, the peak of births
occurring in late April. Since pups are large and swim
from birth, they are not dependent on the steady-
state condition of early April but rather are favored
by the early stages of the ending of that condition,
when the ice sheet begins to deteriorate and retreat
northward. Polar bears and bearded seals are sympat-
ric throughout much of their circumpolar range,
including the Chukchi and northern Bering Sea.
Alertness of mothers and mobility of pups are prob-
ably the specific behaviors which reduce bear preda-
tion on newborn young.
Walruses
The highly gregarious walruses, hke bearded seals,
inhabit ice overlying shallow water. They winter
primarily in the Bering Sea and, although widely
distributed in the pack, they are clumped. Walruses
mainly inhabit those regions of the drifting ice where
leads and polynyas are numerous and where the ice is
thick enough to support their weight, often in dense-
ly packed herds (Fig. 46-5). When ice is at its maxi-
mum extent, individual walruses may be encountered
anywhere in drifting pack where openings are numer-
ous. However, most animals annually occur in two,
or occasionally three, regions: (1) south and south-
west of St. Lawrence Island; (2) the southeastern
Bering Sea, including outer Kuskokwim Bay, south of
Nunivak Island, and western Bristol Bay; and (3)
occasionally northeast of the Pribilof Islands (Burns
790 Interaction of ice and biota
1970, Kenyon 1972, Braham et al. in preparation,
Fay in press).
The calving period is protracted, from March
through early June, with a marked peak in early May
(Burns 1965, Fay in press). Newborn calves are large
and swim from birth. The mother-calf bond is
maintained for up to 24 months. The peak period of
births occurs during the northward spring migration,
at a time when the severity of ice conditions is
rapidly diminishing and therefore presumably poses
little disadvantage to young with limited ability to
swim. The ability of calves to swim at birth enables
them to escape from polar bears. However, in most
years there are few bears in regions where walruses
(especially recently parturient females) are abundant
during April and May. Walruses spend much of their
time resting on the ice. While hauled out, females
protect their calves from the weather by shielding or
brooding them (Fay and Ray 1968).
Polar hears
In most winters the center of abundance for polar
bears is in the flaw zones of the Chukchi and Beau-
fort seas. In some winters they are abundant in the
northern Bering Sea; this phenomenon is usually
associated with the early onset (November-December)
of continuous northerly winds, which drive the heavy
pack southward through Bering Strait. In most years
relatively few bears move into the northern Bering
Sea, and their residence time there is short.
Pregnant females go ashore in November/early
December and make maternity dens in deep snow
drifts which form in ravines, frozen water courses,
and in the lee of steep hills or mountains (Harington
1968). Some denning occurs on heavy drifting ice (J.
W. Lentfer, Alaska Department of Fish and Game,
personal communication) but probably not in the
Bering Sea. Cubs are bom in late December/early
January and they remain in the lair with the mother
until late March or early April. Upon emerging,
mother and cubs (one to three, usually two) move
onto the drifting pack. There are few records of
maternity dens or of sows with new cubs from the
Bering Sea. Dens have been reported on St. Lawrence
Island and near Cape Prince of Wales. Considerations
of physiography enable us to hypothesize that
Figure 46-5. Walruses resting on sea ice, nortiiern Bering Sea, May 1972. Tliese animals utilize ice in preference to land
whenever it is available to them.
Ice as marine mammal habitat 791
pregnant sows probably also den along the rugged and
complex coast of the eastern Chukotsk Peninsula.
Sows with small cubs, presumed to have been born
near where they were seen, have occasionally been
reported near St. Lawrence, King, and Little Diomede
islands; most reports come from residents of Little
Diomede. Cubs may remain with their mothers for
up to 2.5 years (Stirling et al. 1975).
Ice is important to bears as a solid substrate on
which they can move about and hunt (Fay 1974).
Males and nonpregnant females range widely on the
pack in search of prey, mainly ringed seals. Polar
bears are good swimmers and do not hesitate to enter
the water. All of the spotted and ribbon seals, almost
aU of the walruses, and most of the bearded seals in
the Bering Sea during winter are, by virtue of their
distribution, essentially free from predation by bears.
Ringed seals, more abundant in the Chukchi Sea, are
the major prey of bears during venter and early
spring. Bears have become well adapted to hunting
them in leads, at breathing holes, in their snow dens,
and while they are hauled out on the ice (Stirling
1974, Eley 1978). During the winter and early spring
the bears hunt most successfully for these seals along
narrow leads where they wait for seals to surface
(Lentfer, personal communication; Burns, personal
observation; Eley 1978).
during spring migration (Scammon 1874, Durham
1979). The unique structure of the head and lack of
a dorsal fin are thought to be adaptations to ice.
Besides using natural openings in the ice, bowheads
frequently break holes through thin ice— up to 25 cm
or more in thickness, according to Tomilin (1957).
As described by Fay (1974), the head of a bowhead is
highly arched with the blowholes at the apex of a
high promontory (Fig. 46-6), permitting the whales
to breathe in openings too small for their whole
bodies. Personal observations have revealed that this
promontory also provides enough surface relief to
force a small opening in flat, relatively thin ice. In
newly formed or young ice, bowheads surface with
the long axis of the body parallel to the ice. Buoy-
ancy rather than propulsion seems to be used in
surfacing. In two surfacings observed (one of a
wounded whale), only the promontory projected
above the ice surface, which remained unbroken over
the rest of the body.
Bowhead and beluga whales
The relationship of seasonal ice to bowhead and
beluga whales is not understood. It is thought that
virtually the entire population of both bowheads and
belugas wdnters in the seasonal pack of the Bering
Sea. The bowheads move south through the Bering
Strait before and during the formation and influx of
ice (October through December) and migrate north-
ward from March through June. The early part of
the northward spring migration normally precedes
any major deterioration of the pack (in either the
Bering or the Chukchi seas). It does, however,
coincide with the onset of variable ice drift and open-
ing of the pack in the Bering Strait and the southern
Chukchi and adjacent to the fast ice along the central
and northern Chukchi coast. Bowheads are reported
to begin passing through the Bering Strait as early as
mid- to late March in some years (F. Kayouktuk,
Little Diomede Island, personal communication);
they are always in transit during early April. They
begin to appear farther north at Point Hope in
mid-April and pass Point Barrow into the Beaufort
Sea by late April (Durham 1979, Braham and
Krogman 1977). Thus, they penetrate the pack as
much as 3,000 km or more (Tomilin 1957) at a time
when it still remains very extensive. Calves are bom
Figure 46-6. A bowhead whale surfacing in newly formed
ice, northern Bering Sea, April 1966. Circular motion of
the whale has created a small opening in the continuous,
thin ice sheet. Note the lack of a dorsal fin (the object
visible is a harpoon) and the high promontory of the head
in which the blowholes are dorsally situated.
792 Interaction of ice and biota
During the winter, bowheads occur in the ice front
of the central and southwestern Bering Sea (Fay
1974), as well as farther north in such regions of little
compression or of persistent polynyas as occur west
of St. Matthew and southwest of St. Lawrence islands
(Brueggeman in preparation). It is not known wheth-
er bowheads feed while in the Bering.
Belugas are often seen in association with bow-
heads. However, their winter distribution in the
Bering appears to be much broader, including all areas
of persistent polynyas and diverging ice motion from
the Bering Strait southward (Seaman and Burns,
in preparation). These small whales can break
through ice up to at least 10 cm thick. The presence
of food in stomachs of belugas taken at Diomede
Island in March and at other locations from April to
November indicates that they feed throughout the
year.
Some belugas remain in the Bering after the pack is
gone. They head northward starting in March, and
move inshore as soon as ice conditions permit. The
northward migration is well under way in April, often
in association with bowheads (Bums, personal obser-
vation; Lentfer, personal observation; Marquette
1978). From June through October, these whales are
widely distributed in the open sea, along the ice
margin, and in the coastal zone from Bristol Bay
to Amundsen Gulf. Some belugas remain near shore
until the onset of ice formation. In Alaska calving
occurs in ice-free estuaries and embayments from
June to August (mainly in July). It is presumed
that few calves are bom in the summer pack. The
only morphological adaptations of this small whale to
ice appear to be lack of a dorsal fin and significantly
thickened skin on the dorsum, especially of the head.
DISCUSSION
The observed relationship between the annual ice
cycle and the movements, distribution activities, and
adaptations of ice-associated marine mammals indi-
cates a high degree of regularity and repetition in the
distribution and timing of ice features (Burns et al.
1980). We now have some understanding of the
factors contributing to the processes involved in
development, maintenance, and disintegration of the
ice sheet and the various habitats within it. The
result of annually recurring seasonal conditions is an
ice sheet which exhibits a high degree of spatial and
temporal organization.
Physiographic features of the Bering Sea, including
the shelf and shelf break, location, orientation, and
size of islands, and complexity and orientation of the
shoreline, form boundaries or obstacles which con-
strain and shape the ice. Within these boundaries
the seasonally cyclic variables of weather (mainly
temperatures and prevailing winds) and ocean condi-
tions (temperatures, currents, and waves) form,
transport, and deform the ice sheet.
There is relatively little habitat differentiation
during early stages of the autumn /early winter
expansion and development of ice. During this phase
of the annual cycle, clear and definitive associations
of mammals with specific ice habitats are not ob-
vious. Both the ice and the mammals are in a highly
transitory stage of their respective annual cycles.
Progressive development of the ice sheet involves
progressive differentiation of habitats within it.
The array of different habitats specifically utilized by
the various ice-associated marine mammals is achieved
with the onset of a sort of dynamic equilibrium, or
steady state in the ice regime, involving formation,
net southward transport and regional differentiation,
and melting. Depending on prevailing weather during
the periods of ice formation and maintenance, the
extent of the ice sheet and of the habitats within it
may be quite variable in years of weather extremes.
Nonetheless, the habitats previously described are
always developed.
Maximum habitat partitioning of the ice sheet
coincides with its annual maximum differentiation
and extent, attained sometimes by February and
always by March to April. At this time most spotted
and ribbon seals are associated with the front of the
southern pack, adult ringed seals mainly with fast ice
of the coastal zone, and subadult ringed seals, wal-
ruses, bcEirded seals, bowhead whales, beluga whales,
and some polar bears with parts of the remaining
pack where their respective habitat requirements are
met.
Spotted, ribbon, and ringed seals give birth to pups
which remain on the ice for several weeks after birth.
Ringed seals have subnivian lairs. Timing of the
birth periods of these three seals coincides, in most
years, with the maximum extent of their respective
habitats. Ribbon and spotted seals are weaned
(become independent) in three to four weeks after
birth (Burns 1970) and ringed seals in four to six
weeks (McLaren 1958, Burns 1970). Thus, the time
of weaning (and initiation of swimming and diving)
for spotted and ribbon seals occurs at the time when
steady-state ice conditions begin to break up in the
front. Fast ice normally persists into mid-May or
later, providing ringed seals a longer period of time to
complete the weaning process. The similarity of the
pupping periods of these three species is thought to
be the result of parallel evolution favored by the de-
pendable presence of suitable ice as substrate for pups
Ice as marine mammal habitat 793
and the amelioration of ice conditions as swimming
and diving abilities begin to develop. Increased
availability of prey to recently weaned pups, resulting
from amelioration of ice conditions, may also have
helped to establish the optimum time of weaning.
Walruses and bearded seals are both bottom
feeders. They bear large young which, although
limited in swimming and diving abilities, enter the
water shortly after birth. The calving period of wal-
ruses is from March to June; most calves are born in
early May (Burns 1970; Fay, in press). Bearded seals
are born in March to mid-May, mainly in late April
(Burns 1967). In both of these species, most births
occur when the annual steady-state maximum ice
conditions no longer prevail and the ice sheet is
melting and receding northward. The prolonged
birth period with a less pronounced peak than those
of spotted, ribbon, and ringed seals suggests that pres-
ence rather than stability of the ice substrate is more
important to walruses and bearded seals. Bearded
seal pups are weaned in 12-18 days, walruses in 18-24
months (Burns 1970). A more dispersed or broken
ice sheet is favorable to newly independent bearded
seals and to walrus calves remaining with their
mothers.
The disintegration and northward retreat of ice in
the Bering Sea also possess some degree of recogniz-
able organization. The thick floes of the south-
central and southwestern parts of the pack withstand
melting longer than the thinner parts. These thick
floes become detached from the northern pack (cur-
rent gyres and discontinuous regional wind patterns
are suspected to be important causes) and persist as
remnants through June. Other remnants, incorporat-
ing heavy pack, disintegrating fast ice, and river ice,
occur along the Siberian and Alaskan shores through
mid- to late June. These remnants are intensively
used by seals for resting, molting, and passive north-
ward movement. The distribution of pinnipeds in
these remnants reflects the late winter/early spring
distribution patterns: ribbon seals are most abundant
in the western remnant, spotted seals in the central
and nearshore remnants, and young ringed seals in the
nearshore remnants. Walruses, bearded seals, and
adult ringed seals are mostly north of the remnants in
late May and June, moving northward with the
receding main pack (Burns et al. 1980).
Although the basis for association of bowhead and
beluga whales with ice is unknown, their ecological
strategies indicate that ice is a positive rather than
neutral factor in their evolution. During the period
of maximum ice extent in the Bering, bowheads
appear to be more commonly associated with highly
labile portions of the pack (fringe and front) and
northern regions of persistent polynyas or continuous
dispersal. Brueggeman (in preparation) found a
preference by bowheads for regions of 37.5-50 per-
cent of ice cover, a low occurrence (possibly avoid-
ance) of 87.5-100 percent, and non-selective use
of regions of 12.5-25 and 62.5-75 percent of cover-
age. The areas of greatest bowhead density were
in the front and near St. Matthew and St. Lawrence
islands.
Current investigations of belugas (Seaman and
Burns, in preparation) indicate a broader late winter/
early spring distribution than for bowheads, including
all areas where openings in the ice cover are contin-
uously formed. Belugas occur in aU favorable loca-
tions from Bering Strait southward. In comparison to
bowheads (Brueggeman, in preparation), belugas
regularly occur in areas of greater ice coverage and
smaller (although regular) openings. Braham and
Krogman (1977) found that, during the northward
spring migration of bowheads and belugas past Point
Barrow, the belugas begin arriving somewhat earlier
than bowheads and use narrower offshore lead
systems more frequently.
It is not known whether bowheads feed during
winter. They apparently do not feed during their
northward spring migration (Foote 1964, Mairquette
1978). Belugas probably feed in all seasons. Bow-
head calves are born during the spring migration from
May to July (Scoresby 1820, Gray 1887, Maher and
Wilimovsky 1963, Marquette 1978, Durham 1979),
and breeding probably occurs over a long period
beginning in March (Brueggeman, in preparation) and
extending through late summer (Scoresby 1820).
Most observations of suspected breeding are in May
(Foote 1964; Everitt and Krogman 1979; J. Apanga-
look, Gambell, Alaska, and F. Kayouktuk, Little
Diomede Island, Alaska, personal communications).
Birth and most breeding occur in leads and flaw
systems which deeply penetrate a seasonally heavy
and extensive ice cover.
Belugas bear calves in late June through August,
most births occurring from late June to mid-July
(Brodie 1971; Seaman and Burns, in preparation). In
Alaska most, perhaps all, calving occurs in ice-free
waters of the coastal zone. Belugas breed in May
(Sergeant 1962; Seaman and Burns, in preparation),
largely within the ice pack. They probably feed
throughout the year.
The significance of ice to bowheads and belugas is
unknown. Both occur in ice-free waters in summer
and early fall— bowheads in the Beaufort and north-
ern Chukchi seas, and belugas from Bristol Bay to the
southern margin of ice. Both— probably all bowheads
and most belugas— winter in the pack ice of the
Bering Sea.
794 Interaction of ice and biota
It is suggested that this relatively recent habitat,
which existed periodically from late Pliocene through
the Pleistocene (Fay 1974) and regularly throughout
Recent geological time, ±11,000 years (Hopkins
1967), may have represented an extensive new and
vacant niche within which the present adaptations
and associations of bowheads and belugas evolved.
Advantages, other than the availability of productive
shelf waters protected in winter and spring from
prolonged, severe turbulence by ice, are not obvious.
Sergeant and Brodie (1969) suggest that for belugas
ice excludes other delphinids, thus reducing competi-
tion, and killer whales, Orcinus orca, thus reducing
predation. The suggestion applies equally well to
bowheads. Reduction of competition is a more
important effect than elimination of predation.
Killer whales penetrate the southern parts of the
Bering Sea pack, at least by early spring, and range as
far as the northern Chukchi and western Beaufort
seas in summer to mid-autumn (Bee and Hall 1956;
Tomilin 1957; Burns, personal observation). They
occasionally frequent areas where bowheads and,
more often, belugas are present. Belugas react
strongly to killer whale sounds broadcast under water
(Fish and Vania 1971), and confirmed presence of
these predators was reported as the reason why
belugas could not be successfully driven and hunted
at a normally productive hunting site in Kotzebue
Sound (Seaman and Burns, in preparation).
Polar bears are of relatively recent origin. Proto-
polar bears probably began utilizing their arctic niche
by the early to middle Pleistocene (Harington 1964).
For polar bears ice is important as an extensive
substrate on which they travel with ease and search
for their food (Fay 1974). They hunt by various
methods; the most common and productive is "still
hunting," in which the bear sits or lies near a narrow
lead, breathing hole, or lair where its prey, mainly
ringed seals, will surface (Stirling 1974). Bears are
known to take animals up to the size of beluga whales
in this manner (Kleinenberg et al. 1964).
Dispersed ice, which has many constantly changing
openings, probably reduces a bear's chances of
catching seals. One cannot help being impressed
by the behavior and activity patterns of ringed seals
in relation to the more commonly used hunting
strategies of polar bears: few seals haul out in winter
and early spring and therefore hunting by stalking
is less effective. It appears that evolution of polar
bears has been strongly influenced by characteristics
of ringed seal distribution and behavior. But the
hunting strategies of polar bears are directed toward
other prey, particularly bearded seals, as the oppor-
tunity arises.
The strong swimming ability of polar bears is well
knowTi; they have been observed as far as 160 km
from the neeirest land in summer (Q)ritsland 1969).
But such observations are unusual, and these bears
may have been stranded on ice remnants which
melted. The eventual fate of such bears is obviously
not known. Although polar bears are strong swim-
mers, they are not good divers. They enter the water
frequently in the course of traveling, hunting (stalk-
ing), when harassed, to investigate objects (including
ships), and at other times for no apparent reason.
They may enter the water after strenuous exercise to
reduce elevated body temperatures (Q)ritsland 1969).
Stirling (1974) found that in summer young bears
spend more time in the water than adults: during the
course of his observations cubs were in the water 4.5
percent of the time, subadults 8.2 percent, adult
females 0.62 percent, and adult males 0.78 percent.
The annually variable but relatively restricted
northern distribution of polar bears in the Bering Sea
pack is probably a function of the distribution of ice
conditions in which they can travel and hunt most
efficiently. The winter distribution of these bears is
north of the regions in which the highest biomass of
potential prey is present. Thus, bioenergetic consid-
erations appear to be important. It is postulated that
there is a significant energetic advantage to inhabiting
the northern regions of more continuous ice as
opposed to the highly labile and often dispersed
central and southern parts of the pack. In the more
southern parts bears would be forced to swim more
often, and opportunities for successful still hunting
would be greatly reduced. The times of pupping
and molting of pinnipeds in the Bering, when they
would be especially vulnerable to predation by bears,
are close to or after the onset of ice disintegration
and after most bears have returned north (N. Walker,
Kotzebue, Alaska, personal communication; J.
Lentfer, Alaska Department of Fish and Game,
personal communication).
ACKNOWLEDGMENTS
Studies of marine mammal associations with sea ice
were supported in part by the University of Alaska
Sea Grant Program; BLM/OCSEAP contract 035-022-
55 (RU 248/249); and Alaska Department of Fish
and Game Federal Aid in Wildlife Restoration Pro-
jects. Additional logistic support was provided by the
Scripps Institution of Oceanography, U.S. Coast
Guard, U.S. Fish and Wildlife Service, and National
Marine Fisheries Service. We are particularly in-
debted to K. J. Frost, L. F. Lowry, E. S. Muktoyuk,
and L. M. Shults, who participated in field work and
contributed ideas and information.
I
Ice as marine mammal habitat 795
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Ice as marine mammal habitat 797
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I
Birds and the Ice-edge Ecosystem
in the Bering Sea
George J. Divoky
Point Reyes Bird Observatory
Stinson Beach, California
INTRODUCTION
The importance of the marine bird resource in the
Bering Sea has been well demonstrated by Hunt et
al., Chapter 40; Gill and Handel, Chapter 41; and
King and Dau, Chapter 42, this volume. Because sea
ice covers a large portion of the Bering Sea during
the winter and spring, it is of major importance
in determining the distribution and abundance
of seabirds in those seasons. Before discussing the
specific relationships between birds and ice in the
Bering Sea, I will briefly consider the general ways in
which ice can affect bird distribution. The effects
can be divided into detrimental effects (ways in
which ice can decrease bird numbers) and beneficial
effects (ways in which ice can increase bird numbers).
The simplest and most immediate effect of ice
which is important to birds is to decrease surface area
of the water. This affects surface feeders most since,
in general, ice cover of 50 percent reduces feeding
opportunities by half. Diving species are not so
severely affected because, if open water is scattered
throughout the ice, they still have access to much of
the water column and benthos. However, birds diving
under ice may not be able to feed as deep as when ice
is not present because the ice causes a decrease in
light penetration.
The other negative effects ice can have on birds
all relate to ways in which biological productivity is
reduced by the presence of ice. Ice may inhibit
primary productivity in the water column by absorb-
ing solar radiation and reducing the depth of the
euphotic zone (Bunt 1963). Moreover, because ice
prevents wind mixing and its spring melting forms a
surface layer of low density, ice stabilizes the water
column, limiting the up welling of nutrient-rich waters
(Dunbar 1968). Ice scour can greatly reduce benthic
and intertidal biota, food resources of birds. Mol-
lusks, eelgrass, and the fish and zooplankton asso-
ciated with kelp beds are important food sources in
areas unaffected by ice scour.
One of the positive ways in which sea ice can affect
bird distribution is by providing a matrix for an in-ice
phytoplankton bloom (Appollonio 1961). The
importance of the in-ice plankton bloom in the
energy budgets of arctic and subarctic seas has only
recently been realized (Alexander 1974, McRoy and
Goering 1974). In arctic areas with multiyear ice the
in-ice plankton bloom supports a zooplankton and
fish community associated with the underside of the
ice. The under-ice community apparently consists
primarily of copepods and amphipods (Mohr and
Geiger 1968) and two species of fish, arctic cod
(Boreogadus saida) and polar cod (Arctogadus glacial-
is). Because the under-ice fauna is most highly
developed under multiyear ice, in Alaskan waters it is
most important to seabirds in the Beaufort and
Chukchi seas.
Recent studies at the ice edge near Spitsbergen
have shown that a wind-driven upwelling can occur at
the edge of pack ice (Buckley et al. 1979). No direct
evidence of increased primary productivity associated
with such an ice-edge upwelling is yet available. If
such upwelling occurs in the western Arctic it is
probably most important when there is a large section
of ice edge abutting open water, as happens in the
Bering Sea in winter.
Because ice serves as a hauling-out space for marine
mammals, it provides scavenging opportunities for
seabirds in the form of feces, placentas, and carcasses.
It also provides a substrate that allows seabirds to
leave the water to roost. This is probably most
important to species which typically roost on the
shoreline— the Larus gulls, for example. The uneven
upper surface of ice reduces wind speeds and creates a
micro habitat with a reduced wind chill. Since waves
799
800 Interaction of ice and biota
are attenuated by ice cover, surface disturbance of
the water is less next to the ice, and surface feeders
may be able to find prey more readily.
Sea ice is an important factor both proximately
and ultimately in the natural history of seabirds. The
timing of migration and breeding and the location of
wintering areas have been greatly affected by the
yearly increase and decrease of the arctic pack ice.
METHODS
In seven cruises over the past four years the pelagic
avifauna associated with the Bering Sea pack ice has
been studied. On these cruises systematic observa-
tions are made while the ship steams through the ice
and open water adjacent to the ice. Observations are
conducted at 15-minute intervals or stations. For
each station the number of birds per km^ by species
is computed. Information on ice, sea-surface tem-
perature, weather, and distance from land and shelf
break are recorded. Distance from such ice features
as the major leads or the northern edge of the ice
front is obtained later from satellite imagery when
available. We have gathered 1,746 such stations
and are in the final editing stages before beginning
computer analysis with the same types of programs
that George Hunt, Jr., and the University of Rhode
Island have used on open-water pelagic data. We have
until now done only rough calculations with our
observations, but we have obtained a good overview
of the distribution, abundance, and feeding ecology
of the Bering Sea ice avifauna.
Ice formation
Ice begins to form in the northern Bering Sea in
late October and early November and reaches its
maximum extent in January. Because of the poten-
tial dangers involved in operating vessels in areas of
newly forming ice, OCSEAP has not had any ice-edge
cruises during this period and we have no data from
the period of ice formation.
Most species of birds have left the northern Bering
Sea before ice begins to form, and thus few birds are
actually driven south by the newly forming ice.
From observations in the Chukchi Sea in late October
(Watson and Divoky 1972), we know that certain
pelagic species move south with the pack ice. Glau-
cous Gulls (Larus hyperboreus). Ivory Gulls (Pago-
phila eburnea), both murres (Uria spp.), and Black
Guillemots (Cepphus grylle) are the main species
found at the ice edge in the Chukchi that could be
expected to move south with the ice into the Bering.
Ross's Gull (Rhodostethia rosea) is a major compon-
ent of the ice-edge system in the Chukchi, but it
apparently does not move into the Bering Sea in any
numbers. Certain waterfowl, primarily Oldsquaws
(Clangula hyemalis) and eiders, may occupy near-
shore waters until driven south by newly forming ice.
Maximum ice extent
From February through April the Bering Sea pack
ice is at its maximum extent, and this is the period
when its structure is most easily defined. Ice usually
extends as far south as the shelf break. The wind and
wave action from the open water south of the ice
prevents the southern edge of the ice from forming
large floes. This leading edge of the pack ice is
known as the ice front. It is composed of small floes
and ice pans and its extent is dependent on wdnd
conditions. In southerly winds it is compressed into a
band 10-15 km wide directly adjacent to the more
consolidated pack. During northerly winds it can be
as wide as 60 km and is composed of a series of bands
of small floes interspersed with open water. North of
the ice front, the pack ice is composed of large floes
with ice cover of 75-100 percent. The shifting of the
pack by wind and currents is constantly forming new
leads deep in the pack ice, which refreeze as new ones
are formed. Thus the deep pack ice is a dynamic
system of constantly forming and refreezing leads. In
addition, polynyas are associated with islands found
deep in the pack ice. The southward movement of
the pack creates areas of open water on the south
sides of islands. These are the most extensive open-
water areas found deep in the pack ice. (For a
more detailed description, see McNutt, Chapter 10,
Volume 1.)
The first evidence that the Bering Sea ice front is
important to large numbers of birds came from a
group studying marine mammals in the ice front
(Irving et al. 1970). Our March 1976 data demon-
strate the importance of the front at this time (Table
47-1). Cruises since 1976 have shown the same
pattern of distribution for the Bering Sea: moderate-
ly high densities of birds are encountered in passes
in the Aleutians, the lowest densities in open water
off the shelf, moderate densities in open water on the
shelf, and high densities in the ice front over the
shelf.
The 1976 March and April cruises provided us with
good information on the species and densities of birds
in the 60-km ice front. A list of these species, their
average densities, and their location in the front are
presented in Tables 47-2 and 47-3.
Of the species listed in Table 47-2, the Northern
Fulmar (Fulmarus glacialis) and Black-legged Kitti-
wake (Rissa tridactyla) are commonly found over the
open ocean south of the pack and appear to be least
Birds and the ice-edge ecosystem 801
TABLE 47-1
Bird densities (per i<m- )
in the Bering sea: March 1976.
TABLE 47-3
Principal areas of concentration for species
present in Bering Sea ice front in March
Area
Mean
Maximum
density
Unimak Pass
44
212
12
Open water
south of shelf
11
23
28
over shelf
99
300
19
Ice front
561
10,000
103
dependent on ice. The other species may also be
found in open water but occur in higher densities in
the front.
Of these species, the murres are the most abun-
dant. In March 1976 we encountered densities as
high as 10,000/km^ , and densities of 1,000/km^ were
not uncommon. One feeding flock of 25,000 murres
was encountered in the center of a large lead. Three
species of gull are regularly found in the ice front.
Both the Glaucous-winged Gull (Larus glaucescens)
and Glaucous Gull are uniformly distributed in the
ice front from the consolidated pack to open water.
The Glaucous-winged Gull is the more abundant of
the two. In areas west of St. Matthew the Slaty-
backed Gull (L. schist isagus) is also present. Larus
gulls are present in the open water south of the ice
but reach their highest concentrations in the ice
front. The Ivory Gull is present in the ice front in
low numbers. Because it rarely sits on water, in
pelagic situations it requires ice for a roosting site.
Unlike the other gulls present in the ice front, it is
TABLE 47-2
Average densities of species regularly
encountered in the Bering Sea ice front in March
Northern Fulmar
Glaucous Gull
Glaucous-winged Gull
Ivory Gull
Black-legged Kittiwake
Murres
Black Guillemot
Avg. birds per km^
5
5
10
5
10
200
<5
Open water Ice front
h* Northern Fulmar -►<
W — Black-legged Kittiwake H
K Glaucous Gull
1-^ — Glaucous-winged Gull
Ivory Gull
K Murres
Deep pack
-*^
■♦H
-M
Black Guillemot
not found in the open water south of the ice. Obser-
vations in 1973 showed that it does not occur north
of the ice in the more consolidated pack ice. The
Black Guillemot is present in the ice front but is
most abundant in the njore consolidated pack north
of the front, where it occupies the system of con-
stantly forming and refreezing leads.
The polynyas found south of the large islands, hke
St. Matthew and St. Lawrence, support concentra-
tions of Oldsquaws and eiders (Fay and Cade 1959,
McRoy etal. 1971).
Ice decomposition
From April to June the ice in the Bering Sea
decomposes. The ice decomposition, usually por-
trayed as a receding of the ice edge from south to
north, is instead a general decomposition throughout
the pack. The leads do not refreeze as quickly
as they did in winter. Open water thus becomes more
regular in all areas of the pack ice. That the ice
decomposes in this way is important to birds, since
they are able to occupy areas deep in the pack ice as
soon as the ice starts to decompose. For example.
Parakeet Auklets (Cyclorrhynchus psittacula) occupy
the lead near the St. Lawrence Island breeding sites as
soon as it forms (Sealy 1970). In addition to allow-
ing breeding birds to occupy areas near colonies soon
after decomposition begins, the leads also allow
tundra migrants to move north through the pack ice.
The major lead that stretches from the Yukon Delta
to the Bering Strait may be an important migratory
pathway for waterfowl in spring.
802 Interaction of ice and biota
Pelagic observations in April show that the species
found in the ice front in March are still present but
that total numbers average 100 birds/km^ or fewer.
This thinning-out is probably the result of the move-
ment of birds to areas near their breeding sites.
Fulmars and kittiwakes, however, show a marked
increase in frequency and density in the ice front in
April. In May the ice front is not present, and birds
are no more concentrated at the ice edge than they
are deeper in the ice. Densities throughout the ice
between May and June are rather uniform with an
average count of 30-50/km^ . Densities are regularly
over 100/km^ only in areas adjacent to breeding
colonies. Thus the distribution and abundance of
birds are not dependent mainly on food resources as
they are in March but rather on the availability of
nesting sites.
In the period of ice decomposition, the Bering Sea
pack ice harbors more birds than in either of the
other periods.
Trophic relationships
A primary goal of research on ice-associated birds
is to ascertain the principal prey species consumed.
The distribution, abundance, and availability of prey
organisms play major roles in determining seabird
distributions.
The lack of cruises in the fall has made it im-
possible to identify the prey consumed during this
period. Studies at the Chukchi Sea ice edge in late
October show that arctic cod and zooplankton
associated with the underside of the ice are the main
prey consumed by species moving south with the ice
edge (Divoky 1976). As the ice edge moves into the
Bering, where it is composed of first-year ice rather
than the multiyear ice found in the Chukchi, a shift
in food sources must take place.
Specimens have been collected in order to deter-
mine prey items consumed by birds in the Bering Sea
ice front in March and April and throughout the ice
in May and June. Table 47-4 summarizes the infor-
mation obtained from March to June. Pollock
(Theragra chalcogramma) and capelin (Mallotus
uillosus) were the primary prey items during this
time. The only invertebrate that was frequently
encountered is Parathemisto libellula, a major prey
item of the Thick-billed Murre (Uria lomvia). Fish
and zooplankton sampling conducted on the same
cruises show that the prey species listed in Table 47-4
are most abundant near the shelf break in a layer of
warm water near the bottom. The water layer that
contains these species is not uniform in its distribu-
tion along the shelf. The concentration of prey
organisms near the Bering Sea ice front can cause
major feeding flocks to assemble. In March 1976 we
encountered a feeding flock of approximately 25,000
murres with an additional 200-300 gulls. We were
unable to collect birds from the flock, which dis-
persed during our observations. Fish, apparently
driven to the surface by murres, were eaten by the
gulls associated with the flock.
Many of the surface-feeding species present in the
ice front are scavengers. The largest concentrations
of surface-feeding species we have encountered in the
Bering Sea ice front have been associated with factory
ships processing fish. There is little doubt that
these vessels are a major food source for these species.
An apparent increase in the numbers of subadult
Glaucous Gulls in the Arctic in 1978 was thought to
be partially related to the fact that, because of the
food available from factory ships in the Bering Sea,
fewer of the young gulls died over the winter.
DISCUSSION
The antarctic marine ecosystem has a well-
developed pagophilic avifauna, with many species
that breed on ice shelves and utilize the iceberg zone,
ice front, and deeper pack. Many of these species
have specific pagophilic habits: much of their life
TABLE 47-4
Principal prey of four bird species present at the Bering Sea ice edge
Pollock
Capelin
Parathemisto
Euphausiids
Neomysis
Ivory Gull
*
Black-legged Kittiwake
*
*
Common Murre
*
*
Thick-billed Murre
*
Birds and the ice-edge ecosystem 803
depends upon breeding on and feeding next to the
ice. By comparison, the Arctic has a poorly devel-
oped pagophilic avifauna. There are two arctic
species which have major adaptations to the ice
environment: the Ivory Gull and Black Guillemot are
associated with ice throughout the year. Another
species, the Ross's Gull, is associated with ice for
much of the nonbreeding season. The total biomass
of these species is small compared with the remainder
of arctic seabirds or with the antarctic pagophilic
species.
The principal reason for the difference between
the Arctic and the Antarctic is that in the Antarctic
the ice directly abuts ocean on all sides and hence
upwelling can take place on all sides. Most of the
edge of arctic ice is directly surrounded by land. The
arctic ice edge has been shown to be important to
large numbers of pelagic birds only in areas where it
directly abuts subarctic waters, as it does in the
Bering Sea in winter or in certain areas of the eastern
Arctic.
It seems clear that during its formation ice is
mainly restrictive in that it prevents birds from
occupying certain areas of the northern Bering Sea
and, as far as we know, does nothing to increase the
abundance of prey. When ice reaches its maximum
extent its general effect is still to reduce bird numbers
throughout the Bering Sea, but because of high
productivity associated with the ice edge, the pro-
ductivity of pelagic waters is enhanced by the pres-
ence of ice. The ice front can be considered of major
importance because of the large number of birds it
supports. It is also the only habitat utilized by
wintering Ivory Gulls in the western Arctic. On that
basis alone it could be considered critical habitat.
The decomposing ice harbors large numbers
of birds. The relationship of these birds to the
ice is not clear. The phytoplankton bloom that
occurs in the ice in spring is released into the water
but there is no indication that birds benefit directly
by feeding on organisms associated with the phyto-
plankton. The importance of ice to birds in the
spring thus remains unknown.
The analysis of bird densities in and near the
Bering Sea ice will center on determining which
factors play the primary roles in bird distribution.
Factors to be analyzed include distances from the
southern edge of the ice front and the consolidated
pack, ice cover and pattern, sea-surface temperature,
and distance from the shelf break. The results of
these analyses will allow future studies to discover
what processes determine seabird abundance in the
Bering Sea ice-edge ecosystem.
REFERENCES
Alexander, V.
1974 Primary productivity regimes of the
nearshore Beaufort Sea, with refer-
ence to potential roles of ice biota.
In: The coast and shelf of the Beau-
fort Sea, J. C. Reed and J. E. Sater,
eds., 609-32. Arctic Inst. N. Amer.
Arlington, Va.
Appollonio, S.
1961 The chlorophyll content of Arctic
Sea ice. Arctic 14:197-200.
Buckley, J. R., T. Gammelsr^d, J. A. Johannessen,
O. M. Johannessen, and L. P. R0ed
1979 Upwelling: Oceanic structure at
edge of the arctic ice pack in wdnter.
Science 203:165-7.
Bunt, J. S.
1963 Diatoms of antarctic sea ice as agents
of primary production. Nature 199:
1255-2157.
Divoky, G. J.
1976 The pelagic feeding habits of Ivory
and Ross' Gulls. Condor 78: 85-90.
Dunbar, M. J.
1968 Ecological development in polar re-
gions: A study in evolution. Pren-
tice-Hall, Englewood Cliffs, N.J.
Fay,F. H., and T. J. Cade
1959 Ecological analysis of the avifauna of
St. Lawo^ence Island, Alaska, Univ. of
Calif. Pub. Zool. 63:73-150.
Irving, L., C. P. McRoy, and J. J. Burns
1970 Birds observed during a cruise in the
ice-covered Bering Sea in March 1968.
Condor 72:110-12.
McRoy, C. P., and S. R. Goering
1974 The influence of ice on the primary
productivity of the Bering Sea.
In: Oceanography of the Bering
Sea, D. W. Hood and E. J. Kelley,
eds., 403-21. Inst. Mar. Sci., Occ.
Pub. No. 2, Univ. of Alaska, Fair-
banks.
804 Interaction of ice and biota
McRoy, C. P., S. W. Stoker, G. E. Hall, E. Muktoyuk
1971 Winter observations of mammals and
birds St. Matthew Island. Arctic
24:63-5.
Mohr, J. L., and S. R. Geiger
1968 Arctic basin faunal precis— animals
taken mainly from arctic drifting
stations and their significance for
biogeography and water-mass recog-
nition. In: Arctic drifting stations,
J. E. Sater, coordinator, Arctic Inst.
297-313. Arctic Inst. N. Amer.,
Arlington, Va.
Sealy, 8. G.
1970
Watson, G. E.
1972
A comparative study of breeding
ecology and timing in plankton-
feeding alcids (Cyclorrhynchus and
Aethia spp.) on St. Lawrence Island,
Alaska. Master's thesis, Univ. of
British Columbia, Vancouver.
and G.J. Divoky
Pelagic bird and mammal observa-
tions in the eastern Chukchi Sea,
early fall 1970. U.S. Coast Guard
Oceanogr. Rep. 50:111-72.
Section ¥ffl
Mammals
Francis H. Fay, editor
I
Marine Mammals
of the Eastern Bering Sea Shelf:
An Overview
Francis H. Fay
Institute of Marine Science
University of Alaska
Fairbanks
For nearly nine millennia before European man
came to the Bering Sea, the multitudes of whales,
walruses, seals, sea lions, and sea otters residing there
were well known to the native inhabitants of its
shores. For those people, the mammals of the sea
were the very staff of life. Their abundance and
availability were of major importance in the Eskimo
and Aleut hunting cultures (Rudenko 1947, Laughlin
1975). The existence of those multitudes was un-
known to the rest of the world until 1648-49 a.d.,
when the cossacks Stadukhin and Dezhnev first
penetrated to the Bering Sea coast in the Anadyr
district, where they found commercially significant
quantities of walrus ivory (Ray 1975). But it was
not until Vitus Bering's last voyage of discovery in
1741 that real awareness began, for the survivors of
that otherwise ill-fated voyage brought back bundles
of sea otter and fur seal pelts that would bring a
small fortune in trade with China (Berkh 1823,
Chevigny 1965). Over the next two centuries, the
Bering Sea was a busy center of marine mammal
hunting by mariners mainly from Russia and America
for commercial purposes as well as by the native
inhabitants for their subsistence needs. Before they
were through, the commercial hunters had brought
the Steller sea cow to extinction and the sea otter,
the fur seal, the walrus, and the bowhead whale
nearly to extinction (Brandt 1849, Allen 1895,
Roppel and Davey 1965, Kenyon 1969, Bockstoce
1977). The profit incentive for this killing was
unconscionably strong, and the only regulatory
constraints were exerted by world markets for the
products (pelts, ivory, oil, and whalebone) derived
from the animals taken.
Public sentiment against this overkill, late in the
19th century, also was strong, but the means to halt
the killing or even to slow it apparently did not
exist. Although the concept of wildlife management
was at least 2,000 years old, it was not widely applied
(Leopold 1933). To extend it from terrestrial to
marine mammals would require international agree-
ment, for the creatures of the sea were common
property, over which no nation alone could exert
much control. Protective measures for restoring the
fur seal and sea otter eventually were established in
1911 by the North Pacific Fur Seal Convention.
Management-oriented research and experimentation
on the seals were begun at once on the Pribilof
Islands by the (then) U.S. Bureau of Fisheries; this
was the very beginning of research on Bering Sea
mammals. The record of its success with the fur
seals is recognized as one of the world's shining
examples of science in support of wildlife manage-
ment.
Research on other mammals of the Bering Sea
progressed more slowly; it began with Soviet efforts
in the 1930's and 1940's to gain biological under-
standing of walruses, sea otters, and whales in con-
junction with a newly expanded marine mammal
hunting industry of commercial proportions
(Belopolskii 1939, Freiman 1941, Nikulin 1941,
Barabash-Nikiforov 1947, Tomilin 1957). American
research on these mammals began somewhat later
(Brooks 1953, Fay 1957, Rice 1963, Kenyon 1969);
both countries went on to produce studies of the
ice-associated phocid seals (Tikhomirov 1961, 1964a;
Burns 1967, 1970) and Steller sea lions (Mathisen
1959, Kenyon and Rice 1961, Tikhomirov 1964b).
Most of the Soviet contributions were inspired by
the need for biological information on which to
base management plans for commercial harvests,
whereas the main goal of most of the American
807
808 Marine mammals
research was to safeguard the resources of major
importance to the subsistence economy of coastal
residents.
From 1959 to 1972, a large part of the American
research on Bering Sea mammals (other than fur
seals) was conducted by the newly established Alaska
Department of Fish and Game, whose mission was to
provide sound management of the populations
important to the people of coastal Alaska. That
research program was brought almost to a stand-
still with passage by the U.S. Congress of the Marine
Mammal Protection Act of 1972 (P.L. 92-522), which
withdrew all of those mammals from state control
and placed them in the hands of the federal wildlife
agencies. That state of jurisdictional affairs persists,
and only now, eight years later, have those agencies
undertaken a small proportion of the former number
of studies. Fortunately, the NOAA Outer Continental
Shelf Environmental Assessment Program (OCSEAP)
recognized the need for further research and began,
in 1975, a set of studies designed in part to provide
basic information needed to assess the potential
effects of oil exploration and development on the
marine mammals of the Bering Sea shelf. Some of
the studies supported by OCSEAP were landmark
efforts that would not have been feasible otherwise
for logistic reasons. Most importantly, the OCSEAP
studies for the first time began to bring all the marine
mammals of the Bering Sea into focus with their
environment.
The OCSEAP multidisciplinary research over the
past six years, together with the work of the con-
current NSF/PROBES (Processes and Resources of
the Bering Sea Shelf) and NOAA/NMFS fisheries
programs, has produced a bewildering volume of new
biological and oceanographic data that have con-
tributed to a quantum leap in knowledge of the
characteristics and inner workings of the Bering Sea
system. For those of us studying the top-level
consumers in that system, this has been a dream come
true. For years before OCSEAP, we labored long in
virtual isolation over the biology of the different
species, and our view of their environment was
severely limited. Not all the answers to our ques-
tions are available yet, but in this set of volumes
alone lie many that we have long awaited.
Of the 25 species of marine mammals known to
inhabit the Bering Sea (Fay 1974), at least 19 regu-
larly inhabit the shelf. Almost all of the western
Arctic populations of bowhead and beluga whales,
walruses, and bearded, spotted, and ribbon seals
reside there in winter. In summer, the shelf accom-
modates most of the populations of gray whales and
northern fur seals. Some proportions of the western
Arctic ringed seal and polar bear populations also
occur there in winter, and some numbers of North
Pacific fin, minke, humpback, and killer whales and
Dall and harbor porpoises come to the shelf in
summer. Sea otters, sea lions, and harbor seals are
year-round residents of the southern part of the
shelf.
Among the many accomplishments of the OCSEAP
studies of these mammals since 1975 has been to
acquire large quantities of spring-summer distribu-
tional information through aerial surveys and ship-
board sightings, compiled by personnel of the Na-
tional Marine Fisheries Service (NMFS), Seattle.
Major contributions have also been made to our
understanding of the trophic relations of the ice-
associated phocid seals by L. F. Lowry and K. J.
Frost (Chapter 49), of the Alaska Department of
Fish and Game (ADF&G), Fairbanks. This ener-
getic team has provided us also with a synopsis of
published information on the feeding habits of
Bering Sea whales (Chapter 50). A synthesis of
available information on the distribution and num-
bers of sea otters on the southeastern Bering shelf
has been contributed by K. B. Schneider (Chapter
51) of the ADF&G, Anchorage. Reports from studies
complementary to those of OCSEAP have been pro-
vided by G. Y. Harry and J. R. Hartley (Chapter
52), of the NMFS, Seattle, on the distribution and
biology of the Pribilof fur seal population, and by
S. Ashwell-Erickson and R. Eisner (Chapter 53) of
the University of Alaska, Fairbanks, on the ener-
getics of harbor and spotted seals inhabiting the
eastern Bering Sea.
Much more has been learned about the mammals
of the eastern Bering shelf over the past six years
than can be included in this volume. We have gained
much toward understanding the natural history of the
animals and their interrelationships with the environ-
ment, and we can begin to speculate on the poten-
tial effects of OCS oil exploration and development.
Nonetheless, our ability to predict those effects now
or to assess them later, after the fact, will be crude at
best until we have much more information on the
mammals themselves, and more time and help in
assimilating and synthesizing the environmental
data now available. For example, we still know very
little about the population dynamics of most of the
species and almost nothing of their distributions,
movements, and feeding habits in autumn and winter.
For the most part, their responses to a host of poten-
tial physical and chemical perturbations also are
unknown. We assume that all the marine mammals
of the Alaskan continental shelf are food-limited, and
that major damage to any part of their food chains
Overview 809
would have a depressing effect on their popu-
lations. With the present knowledge of most of
the species, however, we probably would have
great difficulty in detecting such a decline,
unless it were very large, and as much difficulty
in identifying the cause.
All the marine mammals now living in the Bering
Sea are predatory carnivores; only the extinct Steller
sea cow was an herbivore. Most of the present popu-
lations are large and consume a substantial propor-
tion each year of the standing stocks of vertebrates
and invertebrates. One can easily see from the
accounts that follow that these mammals could be
major competitors with some of the commercial
fisheries. For the most part, however, they tend to
take smaller organisms and a wider variety than the
fisheries. Some of their prey are predators on or
competitors of commercially valuable species. Bio-
turbation of the bottom sediments by walruses,
bearded seals, and gray whales may have a signifi-
cant positive effect on the system by releasing nu-
trients into the water column that might otherwise be
buried forever. We do not yet know how important
to the system these activities Eire or how many
others, both positive and negative, have escaped our
detection thus far.
Conceptually, the management of marine mammal
populations in concert with their total environment
is widely recognized as the ultimate goal. This is
one of the basic tenets of the U.S. Marine Mammal
Protection Act, as well as of the Fisheries Manage-
ment and Protection Act of 1976 (P.L. 94-265),
and it is one of our own professional goals. This
broad ecological approach is acknowledged to be far
superior to the previously autonomous, single-
species management for maximum sustainable yield.
The prospects for fair dispensation of benefits be-
tween present and future users of the resource would
be dim if all the attendant circumstances of its
existence were not taken into account, and if steps
were not taken to avoid irreversible changes, espec-
ially those resulting from human actions (Holt and
Talbot 1978). In practice, however, ecosystem
management still is an ideal largely beyond the
limits of our understanding of the marine environ-
ment (Estes 1979). At best, it will call for diffi-
cult value judgments, balancing the benefits with the
inevitable costs, at every turn.*
REFERENCES
Allen, J. A.
1895
A synopsis of the pinnipeds, or seals
and walruses, in relation to their
commercial history and products.
In: Fur seal arbitration, 1:367-91.
53rd Cong., 2nd Session, Senate
Exec. Doc. 177. U.S. Gov. Print.
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Barabash-Nikiforov, I. I.
1947 The sea otter. Israel Prog. Sci. Transl.
1962. Nat. Sci. Foundation, Wash-
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Belopolskii, L. O.
1939 On the migrations and ecology of
reproduction of the Pacific walrus
(Odobaenus rosmarus diuergens lUi-
ger). Zool. Zh. (Moscow) 18: 762-74.
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Can., Montreal.
Berkh, V. N.
1823
A chronological history of the dis-
covery of the Aleutian Islands. Ma-
terials for the study of Alaska history.
No. 5., 1974. Limestone Press,
Kingston, Ont.
Bockstoce, J. R.
1977 Steam whaling in the western Arctic.
Old Dartmouth Hist. Soc, New
Bedford, Mass.
Brandt, J. F.
1849
Contributions to sirenology, being
principally an illustrated natural his-
tory of Rhytina. Acad. Imper. Sci.,
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Smithsonian Inst., Washington.
♦Contribution No. 424, Institute of Marine Science, University of
Alaska, Fairbanks.
810 Marine mammals
Brooks, J. W.
1953 The Pacific walrus and its impor-
tance to the Eskimo economy. Trans.
N. Amer. Wildl. Conf. 18:503-10.
Kenyon, K. W.
1969 The sea otter in the eastern Pacific
Ocean. N. Amer. Fauna, No. 68.
U.S. Gov. Print. Off., Washington.
Burns, J. J.
1967 The Pacific bearded seal.
Dep. Fish Game, Juneau.
Alaska
1970 Remarks on the distribution and
natural history of pagophilic pinni-
peds in the Bering and Chukchi Seas.
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Chevigny, H.
1965 Russian America. Binfords and Mort,
Portland, Ore.
Estes, J. A.
1979 Exploitation of marine mammals:
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1957 History and present status of the
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Amer. Wildl. Conf. 22:431-43.
1974 The role of ice in the ecology of
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Sea, D. W. Hood and E. J. Kelley,
eds., 383-99. Inst. Mar. Sci., Occ.
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Freiman, S. lU.
1941 Materials on the biology of the
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Ryb. Khoz. Okeanogr. 20:3-20.
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1975 Aleuts: Ecosystem, Holocene history
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1933
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Mathisen, O. A.
1959 Studies on Steller sea lion (Eumeto-
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Nikulin, P. G.
1941
Ray, D. J.
1975
The Chukchi walrus. Izv. Tikhook.
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1963 Pacific coast whaling and whale
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1965 Evolution of fur seal management
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1978 New principles for the conservation
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1947
The ancient culture of the Bering
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Overview 81 1
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USSR. (IsraelProg. Sci. Transl.)
i
Feeding and Trophic Relationships
of Phocid Seals and Walruses
in the Eastern Bering Sea
L. F. Lowry and K. J. Frost
Alaska Department of Fish and Game
Fairbanks
ABSTRACT
Recent data on food habits of five species of phocid seals
and walruses (Odobenus rosmarus) in the eastern Bering Sea
are reviewed. Harbor seals (Phoca vitulina richardsi), spotted
seals (Phoca largha), and ribbon seals (Phoca fasciata) all feed
to a large extent on pelagic and semidemersal fishes. Demersal
fishes are eaten by all three of these species but appear to be
of greatest importance in the diet of ribbon seals. Crustaceans
and octopus (Octopus spp.) are also eaten. Ringed seals
(Phoca hispida) also feed on pelagic and semidemersal fishes.
Crustaceans make up a considerable portion of the diet of
ringed seals, especially young animals. Bearded seals (Erig-
naihus barbatus) and walruses feed primarily on benthic
organisms. Walruses feed almost exclusively on clams. Clams,
crabs, and shrimp make up the bulk of the diet of bearded
seals. Geographical, seasonal, year-to-year, and age-related
variations in feeding are evident in all species for which suffi-
ciently large samples have been examined. Harbor, spotted,
ribbon, and ringed seals all depend primarily on a pelagic food
web and compete for food with one another and with fur seals
(Callorhinus ursinus), sea lions (Eumetopias jubatus), ceta-
ceans, and seabirds. Walruses and bearded seals compete for
clams in some areas. Gray whales (Eschrichtius robustus) feed
on benthic crustaceans, which are also eaten by bearded seals
and walruses. Commercial fisheries harvest a portion of the
food resource of Bering Sea pinnipeds which may influence
populations of some species. Available data on foods of
phocid seals and walruses are inadequate in all seasons and in
all regions except the northern Bering Sea. Data are lacking
for all species in southern and central regions during winter
months, for walruses in all areas and seasons, and for harbor
seals in the southeastern Bering Sea.
INTRODUCTION
Marine mammals as a group constitute an abundant
and diverse element in the Bering Sea ecosystem.
Within the Bering Sea ecosystem each species must
satisfy its requirements for physical habitat and
biological interactions. Perhaps primary among
biological requirements is the need to find food of
appropriate type and sufficient quantity.
This chapter is about the feeding and trophic
relationships of phocid seals (family Phocidae) and
walruses (Odobenus rosmarus divergens). The seals
are presently considered to be five species: harbor
seal (Phoca vitulina richardsi), spotted seal (Phoca
largha, previously considered a subspecies of Phoca
vitulina, P. v. largha), ribbon seal (Phoca fasciata),
ringed seal (Phoca hispida), and bearded seal (Erig-
nathus barbatus). Major aspects of the distribution
and ecology of these species are well known (see
Burns 1978, Kenyon 1978, and Newby 1978 for
general reviews), and we will mention only those
features of direct relevance to feeding ecology.
Population estimates for seals given here are from
Interagency Task Group (1978).
The food habits of seals have been the subject of
investigation for many years. The earliest accounts
are anecdotal notes in the records of polar explora-
tory expeditions. Researchers soon realized that seals
are better collectors of some fauna, for example
swimming crustaceans, than traditional biological
collecting gear. This led to more rigorous examina-
tion of the contents of many seal stomachs (e.g.,
VanWinkle and Schmitt 1936, Dunbar 1954). How-
ever, most of these studies were concerned with the
nature of the contents rather than the feeding biology
of the seals, except for the study of Dunbar (1941).
The recognition of seals as potential competitors for
commercially important fishes initiated a surge of
research on pinniped feeding habits (Scheffer and
Sperry 1931, Spalding 1964, Rae 1973), but little
attention was given to species in the relatively remote
and inhospitable waters of the Bering Sea. Limited
information for this area is available from American
investigators who worked in coastal villages in the
northern Bering Sea (Kenyon 1962, Burns 1967).
813
814 Marine mammals
More extensive data have come from Soviet studies
conducted in conjunction with commercial harvests
of seals (Shustov 1965; Kosygin 1966, 1971;Goltsev
1971). Recent studies sponsored by the Outer
Continental Shelf Environmental Assessment Program
(OCSEAP) have significantly increased our knowledge
of foods of seals in the Bering Sea. The results of
OCSEAP and Soviet studies provide the basis for the
following discussion of seal food habits.
Foods of walruses have been investigated primarily
as part of descriptive studies of natural history
(e.g., Brooks 1954). The report by Fay et al. (1977)
is of particular interest since it deals with the rela-
tionships of walrus food habits to population size and
available food resources. The following discussion of
walrus food habits is based primarily on the review
and summary by Fay et al. (in preparation).
DESCRIPTION OF FOOD HABITS
Information about the feeding habits of any spec-
ies can be presented in at least two ways. The first is
a quantitative assessment of different prey eaten. A
rigorous quantitative study requires that many speci-
mens be examined throughout the area under con-
sideration and for the whole time the species occurs
there. Information about food clearance rates,
relative digestibility of prey, and the metabolic rates
of the predator is desirable. The second way is
descriptive and indicates the relative importance of
the various prey species. Such descriptive informa-
tion makes it possible to construct food webs, to
distinguish the most important prey species, and to
evaluate trophic interactions. Since the detailed
data required for the first type of presentation are
not available for most species of marine mammals
in the Bering Sea, we present feeding information
at the descriptive level, supplemented with available
quantitative data.
Essentially all of the data available on food habits
of pinnipeds are based on direct examination of
stomach contents. The results of such examinations
are usually presented in one or more of three ways:
(1) percent frequency of occurrence (number of
stomachs in which prey type occurred /total number
of stomachs in sample X 100) of each type of prey,
(2) percentage of each type of prey in the total
number of items eaten, and (3) percentage of each
type of prey in the total weight or volume of con-
tents in a sample (weight and volume are functionally
identical measures, since the specific gravity of most
marine animals is approximately 1.0). The relative
merits of these indices have been discussed by
Spalding (1964). In the following discussion we will
use percent by weight or volume, unless we state
otherwise. We consider this to be the best measure,
since the size of prey consumed by some species
ranges over two orders of magnitude, and other
measures do not take size of prey into account.
Readers should refer to the referenced primary
research reports for more quantitative data.
For purposes of discussion, we have divided the
eastern Bering Sea into four regions, as shovm in
Fig. 49-1. Wherever possible, we will describe food
habits of each species in each region in which it
occurs. Information about each region will be further
broken dowTi if data are available and veiriations
within the region appear significant.
Harbor seal
Harbor seals are year-round residents of the south-
eastern Bering Sea. They occur in substantial num-
bers throughout coastal waters of Bristol Bay and the
Aleutian Islands and in relatively small numbers on
the Pribilof Islands. The total population is estimated
at 30,000 in Bristol Bay and on the Pribilofs and
85,000 in the Aleutians. Large concentrations are
knov^m to occur along the north side of the Alaska
Peninsula around Port Moller and Port Heiden.
The stomach contents of 29 harbor seals collected
at various places in the Aleutian Islands have been
reported (Wilke 1957, Kenyon 1965, Lowry et al.
1979a). Samples from all areas except Amchitka
Island are very small. The reported food items
include fishes, octopus (Octopus sp.,) and crustaceans
(pandalid shrimps and mysids). Fishes eaten included
175' 170-
160^ 155°
\M,
■
NORTHERN
;||j;p;:;s;:;:i- -sp
■
i....
■
•
CENTRAL
BERING
SEA
f ■ :
■ ■
■ SOUTH- !
:
*•» CENTRAL ■
SOUTH-
EASTERN
y*-^
Figure 49-1. Map of the Bering Sea showing regions
discussed in the text.
Phocid seals and walruses 815
walleye pollock (Theragra chalcograinma), Pacific cod
(Gadus macro cephalus), Atka mackerel (Pleuro-
grammus monopterygius), greenling (Hexagrammos
sp.), and sculpins (family Cottidae).
The stomach contents of 15 harbor seals collected
at Otter Island (Pribilof Islands) on 13 April 1979
have been examined (Lowry and Frost, unpublished
data). Eight of these animals had food remains in the
stomach. The composition of the food was 63.5
percent fish, 28.7 percent octopus, 4.6 percent
other invertebrates, and 2.9 percent algae. Fishes
eaten were mostly pollock and Pacific cod, with
smaller numbers of flatfish (family Pleuronectidae),
eelpout (Ly codes sp.), and sculpins.
Although harbor seals are abundant the year round
in Bristol Bay, information on their food habits is
virtually nonexistent. One seal collected in the
drifting ice of southern Bristol Bay in March 1976
had fed entirely on capelin, Mallotus uillosus (Lowry
et al. 1979a). Several species of anadromous and
coastal spawning fishes, including capelin, herring
(Clupea harengus), rainbow smelt (Osmerus mordax),
and salmon (Oncorhynchus spp.), are seasonally
abundant and concentrated in coastal waters of
Bristol Bay (Barton et al. 1977, Macy et al. 1978).
Fishes of the cod and smelt families and herring are
known to be major foods of harbor seals in south
central and southeastern Alaska (Imler and Sarber
1947, Pitcher 1977) and Washington (Scheffer
and Sperry 1931). Recent reports from Bristol Bay
fishermen indicate that large numbers of harbor seals
are associated with schools of herring which spawn in
the area in late May and early June.
Spotted seal
The entire Bering Sea population of 200,000-
250,000 spotted seals inhabits the ice-front zone
during the months of February, March, and April. In
May and June adults and pups are concentrated in
remnants of seasonal ice; subadults appear to have
moved to coastal waters. During the summer and
autumn spotted seals haul out in coastal areas from
northern Bristol Bay to the western Beaufort Sea.
The results of recent Soviet and American studies
on foods of spotted seals in the Bering Sea have been
summarized by Bukhtiyarov et al. (in preparation).
Food from 31 spotted-seal stomachs collected in the
American sector of the Bering Sea in the ice front and
ice remnants during spring months was examined.
Fishes were the major food in all areas. In the
southeastern Bering Sea, capelin were by far the most
important food, followed by herring and pollock.
In the south central and central Bering Sea, pollock
were the major food, and eelpout were also commonly
eaten. In the northern Bering Sea, arctic cod (Boreo-
gadus saida), saffron cod (Eleginus gracilis), and
capelin were all major foods. Pollock, herring, sand
lance (Ammodytes hexapterus), and sculpins were
minor food items in this area. Spotted seals collected
in Soviet waters in the western Bering Sea in spring
were found to have eaten similar species of fishes
(Goltsev 1971, Bukhtiyarov et al. in press.). In
Soviet waters, crustaceans (amphipods, shrimp,
and euphausiids) and octopus are eaten more com-
monly than in the eastern Bering Sea. Crustaceans
appear to be most important to young seals; octopus
are most frequently eaten by adults (Bukhtiyarov et
al. in press).
Except for data collected in spring, little informa-
tion is available about foods of spotted seals in the
Bering Sea. Lowry et al. (1979b) reported saffron
cod, sand lance, herring, smelt, and capelin from 10
spotted seals collected along the southern Seward
Peninsula in late summer and autumn. These species
of fishes are probably the main foods of spotted seals
in the eastern Bering throughout summer and au-
tumn. From observations of foods of ringed seals, it
appears likely that during winter months arctic cod is
also a major food of spotted seals.
Ribbon seal
The Bering Sea population of ribbon seals, number-
ing about 100,000 animals, is found in the Bering Sea
ice front and ice remnants during spring. During
these months the animals pup, breed, and molt and
spend little time feeding. Although there is little
direct evidence, ribbon seals are thought to spend the
remainder of the year feeding pelagically near the
Bering Sea shelf break (Bums, in press).
All major studies of foods of ribbon seals have
been based on animals collected during the spring
period of reduced feeding. Shustov (1965) examined
the stomachs of 1,207 seals taken in the ice front of
the Bering Sea (between St. Matthew and St. Law-
rence islands and the Gulf of Anadyr) from March to
July. Only 32 stomachs contained recognizable food,
mostly shrimps, amphipods, mysids, and cepha-
lopods. Several species of fishes, particularly arctic
cod, saffron cod, and herring, were eaten, but not
frequently.
The results of recent American studies on foods of
ribbon seals in the Bering Sea were summarized by
Frost and Lowry (1980). Animals were collected in
the months of March to June. Food remains were
found in the stomachs of seven of 61 animals exam-
ined. By collecting otoliths from small intestines, we
obtained data on the species of fish consumed by a
total of 28 animals. Trace amounts of invertebrates
816 Marine mammals
(octopus beaks, fragments of shrimps and small
clams) were found in 11 of the 28 specimens exam-
ined. In the south central Bering, pollock were the
most numerous prey, and capelin and eelpout were
also eaten in substantial numbers. In the central
Bering, pollock were again the numerically dominant
prey, followed by eelpout, Greenland halibut (Rein-
hardtius hippoglossoides), pricklebacks (Lumpenus
spp.), and capelin. North and east of St. Lawrence
Island arctic cod were the major food; saffron cod,
sculpins, octopus, and pollock were occasionally
eaten. On the basis of the size of otoliths recovered
and the relationship between fish weight and otolith
length, eelpout eaten were about nine times heavier
than pollock. Eelpout may be a more important food
in the south central and central Bering Sea than is
indicated by the number consumed.
Burns (in press) reported the stomach contents of
two ribbon seals collected in the Bering Sea in Febru-
ary. One of the seals had eaten exclusively pollock,
the other arctic cod. Each of these stomachs con-
tained over a liter of food. Unfortunately, these are
the only data available on the foods of ribbon seals
during the period of active feeding.
Ringed seal
Ringed seals are the most widely distributed and
abundant pinnipeds in the northern hemisphere.
They occur seasonally in the Bering Sea, appearing
with the formation of seasonal sea ice in November
and leaving when ice is disintegrating in May and
June. They are found primarily in coastal areas
where shorefast ice provides a stable substrate for the
care and weaning of pups. Ringed seals of the Bering,
Chukchi, and Beaufort seas appear to constitute a
single population estimated to number 1-1.5 million.
Although foods of ringed seals in various parts of
their range have been studied extensively, until
recently there was only one published report on
foods of ringed seals in the Bering Sea. That study
(Kenyon 1962) reported the stomach contents of 14
seals collected at Diomede in the spring of 1958.
Recent studies (Lowrry et al. 1979b and 1980a),
based primarily on collections made at Eskimo
hunting villages, have considerably expanded our
information. Most of the specimens have been
collected at the northern Bering Sea villages of Nome,
Gambell, Savoonga, Diomede, and Wales. At all
locations, over 80 percent of the stomach contents in
samples of ringed seals was made up of three or
four of the following prey: arctic cod, saffron cod,
sculpins, shrimps, mysids, and gammarid amphipods.
The major prey utilized vary both seasonally and
geographically. Saffron cod are most important in
the diet during fall and spring months along the
mainland coast. Arctic cod are the main species eaten
during winter months in the northern Bering.
Shrimps are eaten in small amounts in all areas and
at all seasons but are of greatest importance in spring
and summer in the northern Bering and Norton
Sound. Mysids are eaten in largest quantities in the
southeastern Bering and near St. Lav^rrence Island.
Gammarid amphipods and sculpins are eaten most
commonly near St. Lawrence and Little Diomede
islands.
Samples collected have been large enough to
test for age- and sex-related dietary differences.
Foods of male and female ringed seals collected in the
Bering Sea were similar (Lowry et al. 1980a). How-
ever, major differences were found in the relative
importance of the various prey types in different age-
classes of seals collected in spring (Lowry et al.
1980a). Crustaceans (primarily shrimps, mysids, and
amphipods) made up 98 percent of the food of
recently weaned pups, 77 percent of the food of
yearlings, 40 percent of the food of two- to four -year-
old seals and 20 percent of the food of seals five or
more years old. The importance of fish in the diet
showed a corresponding increase with age.
Year-to-year variations in the primary prey at a
single locality and season have also been documented.
Data are available on the foods of ringed seals at
Diomede for seven spring hunting seasons between
1958 and 1978. Shrimp and arctic cod were each the
primary food in three of the seven years, and gam-
marid amphipods in one year (Kenyon 1962, Lowrry
et al. 1979b). Since these differences showed no
systematic pattern, they are probably related to
annual differences in relative abundance of the
various prey species.
Bearded seal
Bearded seals are circumpolar in distribution and
common throughout areas of moving ice in the Bering
Sea. Like ringed seals, they occur only seasonally in
the Bering Sea, in months when ice is present.
Bearded seals in the Bering and Chukchi seas are
considered a single population numbering about
300,000.
Results of Soviet investigations on foods of
bearded seals in the Bering Sea have been reported by
Kosygin (1966, 1971). Kenyon (1962) reported on
the stomach contents of 17 bearded seals taken at
Diomede in spring 1958. Burns (1967) reported
the results of his examinations of 23 bearded seal
stomachs collected in the northern Bering and Chuk-
chi seas. Results of recent American studies based
primarily on specimens collected at coastal villages
Phocid seals and walruses 81 7
have been summarized by Bums and Frost (1979)
and Lowry et al. (1980b). Most specimens used in
both Soviet and American studies have been collected
in spring.
Throughout the Bering Sea, crabs (Chionoecetes
opilio and Hyas spp.), shrimps (Argis spp., Crangon
spp., Eualus spp. and Pandalus spp.), and clams
(mostly Serripes groenlandicus) make up the bulk of
the diet of bearded seals. Fishes are generally of
little importance; those most commonly eaten
are sculpins and saffron cod. Kosygin (1971) re-
ported snails, octopus, and flatfish as important
foods and did not find Serripes in his samples.
Geographical variations in the relative importance
of the major prey species are evident (Lov^y et al.
1980b). Shrimps comprise a relatively constant
proportion of the food, ranging from 16 to 33
percent. The species of shrimps eaten vary in relation
to patterns of shrimp distribution. Similarly, Chio-
noecetes (Tanner crab) is the main species of crab
eaten in offshore vi^aters of the southeastern and
south central Bering, and Hyas (spider crab) is more
commonly eaten nearshore and in the northern
Bering. The proportion of clams in the diet is highly
variable, ranging from 4 to 69 percent, depending on
locality. The proportions of clams and crabs appear
to be inversely related: in areas where large amounts
of clams are consumed, crabs are not eaten in quan-
tity. Sculpins were found in particularly large quanti-
ties in bearded seals taken at Diomede.
Differences in foods of male and female bearded
seals are slight and probably not significant, but
age-related changes in foods are marked. The impor-
tance of clams in the diet increases with age, and the
amount of shrimps consumed decreases. Recently
weaned pups eat saffron cod almost as frequently
as sculpins; more than 75 percent of the fishes eaten
by older seals are sculpins (Lownry et al. 1980b).
Seasonal changes in major food items are also
marked. Clams are eaten in significant amounts only
during spring and summer months. The proportion
of shrimps and crabs in the diet is highest during fall
and winter.
Data on foods of bearded seals taken during spring
at Diomede are available for seven years during the
period 1958-79 (Kenyon 1962, Lowry et al. 1980b).
Clams were the main food found in 1958 and 1967.
Since 1975 clams have been a minor component of
the food, accounting for less than 10 percent of the
stomach contents.
Walrus
The Pacific walrus population ranges seasonally
throughout the waters covering the Bering-Chukchi
platform. Since they are benthic feeders, they do not
regularly occur in deep waters off the continental
shelf. During winter and spring months walruses
are found throughout areas of moving ice in the
Bering Sea and Bristol Bay. Much of the population
moves north through Bering Strait as seasonal ice
disappears. Several thousand walruses summer on
coastal haulouts in Bristol Bay and the northern
Bering Sea. Recent estimates indicate a population of
more than 200,000 (Krogman et al. 1979).
The only significant published accounts of foods of
walruses in the Bering Sea are those of Fay et al.
(1977 and in preparation). The following summary is
taken directly from those reports.
Analysis of the contents of the stomachs of 21
walruses collected in March and April 1976 in the
southeastern Bering Sea showed that the major foods
were clams (mostly Serripes groenlandicus and
some Mya truncata). Tanner crabs, and snails (Nep-
tunea sp. and Buccinum sp.).
Fay et al. (in preparation) reported on the stomach
contents of 107 walruses taken at five locations in the
northern Bering Sea between April and June in
1974-76. The results are summarized in Table 49-1.
Five genera of clams (Mya, Serripes, Hiatella, Spisula,
and Clinocardium) made up 85-99 percent of the
identifiable food at all locations. Other prey items
such as crustaceans, worms, tunicates, and echino-
derms were of only minor importance in the diet.
Mya was the primary prey at all locations except
south of Nome, where Serripes made up 98 percent
of the identifiable stomach contents.
Although the same array of species is eaten by
both male and female walruses, in the northern
Bering Sea females tended to eat smaller clams than
males. Females ate the smaller species such as Hiatel-
la and small clams of such large species as Mya
and Serripes. Males fed primarily on large clams of
large species, particularly Mya.
Age-related differences in diet have not been
rigorously examined. Fay et al. (in preparation)
suggest that young animals may feed on smaller prey
than adults.
FOOD WEBS
The observed foods of seals and walruses at a given
place and time are influenced by a complex set of
factors. We consider that there are three major
categories of interacting elements that determine
observed feeding patterns. First are the anatomical
and physiological adaptations of the predators which
allow them to survive in a given habitat, dive to a
certain depth, and capture, consume, and process a
818 Marine mammals
TABLE 49-1
Food identified from stomachs of 107 walruses taken in the northern Bering Sea, April to June 1974-76.
Only prey items which accounted for more than 1 percent of the total sample are listed.
Sample size at each area is given in parentheses. From Fay et al. (in preparation).
Ranking
of prey
West of St. North of St.
Lawrence L (13) Lawrence L (14) South of Nome (7)
King L (2) Bering Strait (71)
Mya
Mya
Hiatella
Serripes
Serripes
Spisula
Spisula
Clinocardium
Hyas
Serripes
Mya
Spisula
Mya
Spisula
Hiatella
Serripes
Erignathus
certain type of prey. Second are the various charac-
teristics of the prey populations, of which distribu-
tion and abundance aire most important at the empir-
ical level. Third are the various behavioral adapta-
tions of specific predator and prey species and the re-
sultant interactions betw^een these species. Obviously
the first and third of these categories are determined
by evolution and are quite stable over the short time
in which our observations are made. Such adapta-
tions are important in determining the spectrum of
possible prey species and observed preference for
particular prey. Most of the variability in observed
foods can probably be explained by patterns of
variation in the distribution and abundance of appro-
priate prey species. This is a particularly important
and labile interaction since prey populations can
fluctuate wddely over short periods in response to
such conditions as seawater temperature, intensity of
commercial fishing, and perhaps offshore oil and gas
development.
Since the actual species of prey consumed by seals
vary greatly, both geographically and seasonally, a
single diagrammatic food web dealing with the
specific prey species would be extremely difficult to
construct or understand. Consequently, we will deal
with the major types of prey involved in seal and
walrus food webs. The various types of prey con-
sumed by seals and walruses can be divided into six
major categories. The prey types and major species
included in each are shown in Table 49-2.
Fig. 49-2 shows a generahzed food web for harbor,
spotted, ribbon, and ringed seals. Only major trophic
connections among the various types of organisms are
shown. Four prey types are significant sources of
food for these species of seals. However, most of the
food of each species of seal is derived from the
pelagic portions of the food web. Energy transfers in
the pelagic subsystem are generally direct. For
example, a ringed seal may eat euphausiids which
have been feeding on diatoms. This involves only two
energy transfers between producer and top consumer.
But as many as four energy transfers may be in-
volved, for example, dino flagellate ^ small copepod ^
hyperiid amphipod ■* pollock ^ ribbon seal.
A generalized food web for bearded seals and
walruses is shown in Fig. 49-3. Both of these species
derive most of their food from benthic organisms.
Walruses feed almost exclusively on clams, which feed
mostly on detritus and phytoplankton. Although
bearded seals also derive some of their nutrition from
such short energetic pathways, their trophic resource
base is more diverse. Bearded seals may feed as many
as four energetic steps from producers, as in the
following: phytoplankton ^ clam ->■ Tanner crab ^
sculpin ^ bearded seal.
TROPHIC INTERACTIONS
From the preceding discussion of food habits
and food webs it is obvious that there is considerable
overlap in the types and particular species of prey
consumed by seals and walruses. Two other species of
pinnipeds, the northern fur seal (Callorhinus ursinus)
and the Steller sea lion (Eumetopias jubatus) are also
abundant in the Bering Sea and compete for food
with phocid seals. The relative importance of the
various prey types to all species of Bering Sea pinni-
peds is shown in Table 49-3.
Bearded seals and walruses are the only pinnipeds
in this area that feed predominantly on benthic
organisms. The major features of distribution and
movements of these two species are also similar.
However, competition for food is minimized by the
fact that much of the diet of walruses is made up of
burrowing infaunal clams which are generally not
eaten by bearded seals. The two species do compete
Phocid seals and walruses 819
TABLE 49-2
List of major species included within six types of prey directly
consumed by seals and walruses in the Bering Sea.
Prey type
Major species
I
I
Pelagic and
semidemersal
fishes
Demersal
fishes
Pelagic
nektonic invertebrates
Nektobenthonic
invertebrates
Epifaunal
invertebrates
Infaunal
invertebrates
Walleye pollock, Theragra chalcogramma
Saffron cod, FAcginus gracilis
Arctic cod, Boreogadus saida
Pacific cod, Gadus macroccphalus
Capelin, Mallotus villosus
Rainbow smelt, Osinerus inordax
Herring, Clupca harengus
Eelpout, Lycodes spp.
Sculpins, Myoxoccphalus spp., Gymnocanilius spp., Icelus spp.
Flatfish, Reinhardtius hippoglossoides, Limanda aspera, Lepidopsetta bilincata, Hippoglossoides spp.
Sand lance, Ammodytes hexapterus
Euphausiids, Thysanoessa spp.
Hyperiid amphipods, Parathemislo spp.
Mysids, Neomysis rayi, Mysis spp.
Shrimps, Pandalus spp., Eualus spp., Crangon spp., Argis spp.
Gammarid amphipods, ^mpc//sca spp., Anonyx nugax, Gamrnarus spp.
Octopus, Octopus spp.
Crabs, Chionoecetes opilio, Hyas spp.
Sr\&\\s , Buccinum spp., Natica spp., Poliniccs spp., Neptunca spp.
C\ams, Serripes groenlandicus, Mya truncata, Spisula polynyma, Hiatclla arctica, Clinocardium
cilia turn
Polychaete worms, Nephthys sp., Lumbrinercis sp.
Echiuroid worms, Echiurus echiurus
Priapulids, Priapulus caudatus
for Serripes, and there are indications that the com-
bined predation on this species is in excess of the
sustainable yield. The amount of Serripes found in
bearded seals taken at Diomede has decreased in
recent years; the decrease is closely correlated with an
increase in the numbers of walruses summering in
Bering Strait (Lowry et al. 1980b).
Gray whales (Eschrichtius robustus) forage in the
Bering Sea during summer months. They consume
mostly benthic epifauna and nektobenthos
(Zimushko and Lenskaya 1970) and compete for
food with bearded seals and, to a lesser extent, with
ringed seals. In the northern Bering Sea much of the
diet of both gray whales and ringed seals consists of
gammarid amphipods. The combined foraging
activities of bearded seals, walruses, and gray whales
undoubtedly influence the structure of benthic
communities and food webs.
Pelagic and semidemersal fishes comprise a major
portion of the diet of all other species of pinnipeds in
the Bering Sea. Pollock and capelin are the primary
species eaten in the southern Bering, arctic and
saffron cod are the major species in the northern
Bering, and herring and smelt aire seasonally impor-
tant throughout coastal waters. Although foraging
activities of many species are geographically or
temporally offset, more than 2 million pinnipeds
are being supported primarily by this fish resource.
Moreover, the same species of fishes are consumed in
large numbers by some species of whales and dolphins
(Frost and Lowry, Chapter 50, this volume) and
seabirds (Divoky 1977, Hunt 1978). The importance
of whales in this system is magnified by the fact that
they also consume planktonic and pelagic nektonic
invertebrates, which are the main foods of pelagic and
semidemersal fishes. If the pelagic trophic subsystem
820 Marine mammals
PELAGIC NEKTONIC
INVERTEBRATES
PLANKTONIC ► PELAGIC &
INVERTEBRATES SEMIDEMERSAL
FISHES
PHYTOPLANKTON
i
HARBOR, SPOTTED
RIBBON, RINGED
SEALS
MACRO
IN- AND EPIFAUNAL -^
JNVERTEBRATES
•NEKTOBENTHONIC
INVERTEBRATES
n
MICRO
IN- AND EPIFAUNAL
INVERTEBRATES
DETRITUS
BACTERIA
Figure 49-2. Generalized food web for harbor, spotted,
ribbon, and ringed seals in the Bering Sea.
BEARDED SEALS
NEKTOBENTHONIC
INVERTEBRATES
INFAUNAL
NVERTEBRATES
PHYTOPLANKTON
BENTHIC ALGAE
DETRITUS
BACTERIA
Figure 49-3. Generalized food web for bearded seals
and walruses in the Bering Sea.
is in equilibrium, changes in population size of
one consumer species will affect other consumer
populations.
People also compete directly w^ith pinnipeds
for food. Commercial fisheries can alter not only the
total standing stock of fishes (or shellfishes) in a given
area but also the proportion of individual fish species
in the biomass. Changes in composition of the fish
fauna apparently induced by fishing have been
documented for the North Sea (May et al. 1979) and
have probably also occurred in the Bering Sea (Pruter
TABLE 49-3
Relative importance of major prey types in the diet of pinnipeds in the eastern Bering Sea.
Pelagic and
Pelagic
Epifaunal
Infaunal
Predator
semidemersal
Demersal
nektonic
Nektobenthonic
benthic
benthic
species
fishes
fishes
invertebrates
invertebrates
invertebrates
invertebrates
Harbor seal
Major
Minor
Minor
Spotted seal
Major
Minor
Major for juveniles
Minor for adults
Major for juveniles
Ribbon seal
Major
Major
Minor
Ringed seal
Major
Minor
Major
Major
Bearded seal
Minor
Major
Major
Major in
some areas
Walrus
Minor
Minor
Major
Fur seal
Major
Major (Squids)
Sea lion
Major
Minor
Minor
Phocid seals and walruses 821
1973). Such changes undoubtedly affect the compet-
itive balance among pinniped populations. It is
impossible now to predict what the effects on pinni-
peds might be, because we lack data on the suitability
of various prey species and the mechanisms and
magnitude of responses to changes in the availability
of prey.
Consumption of marine organisms by pinni-
peds and removal by commercial fisheries have
in common the effect of reducing the standing stock
of the prey or target species. The effects of pinniped
consumption and commercial fisheries can therefore
be considered complementary. Extant models which
deal with consumption of finfish by pinnipeds
compute total consumption based on estimates of
population size, mean weight of pinnipeds, residence
time in the area, food consumption rates, and propor-
tion of fish in the diet (McAlister and Perez 1976).
With the exception of body weight, the statistics for
most species are based on few data and are therefore
subject to great inaccuracies. Nonetheless, the results
of such an exercise indicate that more finfish are
consumed by pinnipeds than are caught by commer-
cial fisheries in the Bering Sea (McAlister and Perez
1976). Considerable refinement in the data is re-
quired before such a model can be of practical use in
evaluating pinniped-fisheries interactions in the
Bering Sea.
TABLE
During the period 1968-77 the total commer-
cial catch of pollock in the Bering Sea and Aleutian
Islands averaged slightly over 1.3 million mt per year
(North Pacific Fishery Management Council 1978).
This biomass of fish is equivalent to the amount
consumed annually by approximately 600,000
pinnipeds weighing 100 kg apiece and eating 6
percent of their body weight per day. Thus, if
pinniped populations in the Bering Sea are food
limited, the pollock fishery alone may play a major
role in limiting pinniped numbers. Conversely, the
number of fish available to commercial fishermen
could be increased by reducing the size of pinniped
populations. Multispecies management in such cir-
cumstances is obviously desirable and necessary for
maintenance of long-term ecosystem stability (May
etal. 1979).
Major data gaps
Although recent efforts have added considerably to
our knowledge of the foods of seals and walruses in
the Bering Sea, substantial data gaps still exist. A
matrix of areas and seasons for which data are inade-
quate to describe food habits is given in Table 49-4.
Data from the northern Bering Sea are more near-
ly adequate than from any other area, largely be-
cause specimen material is available from Eskimo
49-4
Major gaps in the data base on foods of phocid seals and walruses in the Bering Sea.
For each area-season combination, species listed are those for which data
are inadequate at the descriptive level.
Season
Southeastern
South central
Area
Central
Northern
Autumn
Sept-Nov
Harbor seal
Walrus
Ribbon seal
Ribbon seal
Walrus
Winter
Dec-Feb
Harbor seal
Spotted seal
Bearded seal
Walrus
Spotted seal
Ribbon seal
Bearded seal
Walrus
Bearded seal
Ringed seal
Spotted seal
Ribbon seal
Walrus
Walrus
Spring
Mar-May
Harbor seal
Ringed seal
Bearded seal
Walrus
Bearded seal
Walrus
Ringed seal
Bearded seal
Walrus
Summer
June-Aus
Harbor seal
Spotted seal
Walrus
Ribbon seal
Ribbon seal
822 Marine mammals
subsistence harvests. Generally, data from other Burns, J. J.
areas must be obtained from collections made for 1967
scientific purposes. Such collections usually require
the support of large, ice-reinforced vessels, which are
costly and have only been available during spring
months. Many of the present data gaps could be
filled if adequate ship support were available during
winter months.
In addition to descriptive information on food
habits, many other types of data are needed in order
to understand the trophic relationships and feeding
ecology of marine mammals. Information is needed
on selectivity (preference), suitability of alternate
foods, feeding and digestive rates, the nature and
causes of year-to-year variations in foods, and the
responses of individuals and populations to variations
in the availability of food. Many years of study wiU
be required to gather adequate information on these
topics. However, in view of the resource values of
pinnipeds and the species on which they prey, it is
essential that research be initiated where important
knowledge gaps exist and be continued or accelerated
to fill in data inadequacies in areas presently under Divoky G. J.
study. 1977
The Pacific bearded seal. Alaska Dep.
Fish and Game, Juneau.
1978 Ice seals. In: Marine mammals of
eastern North Pacific and arctic
waters, D. Haley, ed., 193-205.
Pacific Search Press, Seattle, Wash.
The ribbon seal. In: Handbook of
marine mammals, R. J. Harrison and
S. H. Ridgway, eds. Academic Press,
London (in press).
Burns, J. J., and K. J. Frost
The natural history and ecology of the
bearded seal, Erignathus barbatus.
In: Environmental assessment of the
Alaskan continental shelf. NOAA/
OCSEAP, Final Rep. (in press).
The distribution, abundance and feed-
ing ecology of birds associated with
pack ice. In: Environmental assess-
ment of the Alaskan continental
shelf. NOAA/OCSEAP, Ann. Rep.
2:525-73.
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Barton, L. H., I. M. Warner, and P. Shafford
1977 Herring spawning surveys— southern
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NOAA/OCSEAP (Final Rep.), Ann.
Rep. 7: 1-112.
Brooks, J. W.
1954
A contribution to the life history and
ecology of the Pacific walrus. Alaska
Coop. Wildl. Res. Unit, Univ. of
Alaska, Fairbanks.
Bukhtiyarov, Y. A., K. J. Frost, and L. F. Lowry
New information on the foods and
feeding habits of the larga seal (Phoca
largha) in the Bering Sea in spring.
In: Pinnipeds of the North Pacific
region, F. H. Fay, ed. Soviet-Ameri-
can Coop. Studies on Mar. Mammals
(in prep).
Dunbar, M. J.
1941 On the food of seals in the Canadian
eastern arctic. Can. J. Res. D. 19:
150-5.
1954 The amphipod Crustacea of Ungava
Bay, Canadian eastern arctic. J. Fish.
Res. Bd. Can. 11:709-98.
Fay, F. H., Y. A. Bukhtiyarov, S. W. Stoker, and
L. M. Shults
Food of the Pacific walrus in the
winter-spring period in the Bering
Sea. In: Pinnipeds of the North
Pacific region, F. H. Fay, ed. Soviet-
American Coop. Studies on Mar.
Mammals (in preparation).
Fay, F. H., H. M. Feder, and S. W. Stoker
1977 An estimation of the impact of the
Pacific walrus population on its food
resources in the Bering Sea. Mar.
Mamm. Comm., Rep. MMC-75/06,
74/03.
Phocid seals and walruses 823
Frost, K. J., and L. F. Lowry
1980 Feeding of ribbon seals (Phoca fas-
ciata) in the Bering Sea in Spring.
Can. J. Zool. 58:1601-7.
Goltsev, V. N.
1971 Feeding of the common seal.
Ekologiya 2: 62-70.
Hunt, G. L., Jr.
1978 Reproductive ecology, foods and
foraging areas of seabirds nesting on
the Pribilof Islands. In: Environ-
mental assessment of the Alaskan
continental shelf. NOAA/OCSEAP,
Ann. Rep. 1: 570-775.
Imler, R. H., and H. R. Sarber
1947 Harbor seals and sea lions in Alaska.
U. S. Fish Wildl. Serv. Spec. Sci.
Rep. 28.
Interagency Task Group
1978 Final environmental impact state-
ment: Consideration of a waiver of
the moratorium and return of manage-
ment of certain marine mammals to
the State of Alaska. U.S. Dep. Comm.,
U.S. Dep. Interior, Washington,
D.C.
Kenyon, K. W.
1962 Notes on the phocid seals at Little
Diomede Island, Alaska. J. Wildl.
Man. 26:380-7.
1965 Food of harbor seals at Amchitka
Island, Alaska. J. Mammal. 46:
103-4.
1978 Walrus. In: Marine mammals of
eastern North Pacific and arctic
waters, D. Haley, ed., 178-83. Pacific
Search Press, Seattle, Wash.
Kosygin, G. M.
1966 Some data on food and food habits
of lakhtak (bearded seal) during
spring and summer in the Bering Sea.
Izv. TINRO 58:153-7.
1971 Food of the bearded seal, Erignathus
barbatus nauticus (Pallas), of the
Bering Sea in the spring-summer
period. Izv. TINRO 75:144-351.
(Transl. from Russian Fish. Mar.
Serv., Transl. Ser. No. 3747.)
Krogman, B. D., H. W. Braham, R. M. Sonntag, and
R. G. Punsly
1979 Early spring distribution, density and
abundance of the Pacific walrus
(Odobenus rosmarus) in 1976. In:
Environmental assessment of the
Alaskan continental shelf. NOAA/
OCSEAP, Final Rep.
Lowry, L. F., K. J. Frost, and J. J. Burns
1979a Potential resource competition in the
southeastern Bering Sea: Fisheries and
phocid seals. Proc. 29th Alaska Sci.
Conf., Fairbanks, 15-17 August 1978,
287-96.
1979b Trophic relationships among ice in-
habiting phocid seals. In: Environ-
mental assessment of the Alaskan
continental shelf. NOAA/OCSEAP,
Ann. Rep. 1:35-143.
1980a Variability in the diet of ringed
seals Phoca hispida, in Alaska. Can.
J. Fish. Aquat. Sci. 37:2254-61.
1980b Feeding of bearded seals in the
Bering and Chukchi seas and tropic
interaction with Pacific walruses.
Arctic 33:330-42.
Macy, P. T.,
Mason
1978
J. M. Wall, N. D. Lampsakis, and J. E.
Resources of non-salmonid pelagic
fishes of the Gulf of Alaska and
eastern Bering Sea. NW and Alaska
Fish. Cent., NMFS, Seattle, Wash.
May, R. M., J. R. Beddington, C. W. Clark, S. J. Holt,
and R. M. Laws
1979 Management of multispecies fisheries.
Science 205:267-77.
McAlister, W. B., and M. A. Perez
1976 Ecosystem dynamics birds and marine
mammals. Nat. Mar. Fish. Serv.
N.W. and Alaska Fish. Cent. Proc. Rep.
824 Marine mammak
Newby, T. C.
1978 Pacific harbor seal. In: Marine mam-
mals of eastern North Pacific and
arctic waters, D. Haley, ed., 185-91.
Pacific Search Press, Seattle, Wash.
North Pacific Fishery Management Council
1978 Fishery management plan and draft
environmental impact statement for
the groundfish fishery in the Bering
Sea/Aleutian Island area. N. Pac.
Fish. Man. Council, Anchorage, Alas-
ka.
Pitcher, K. W.
1977
Population productivity and food
habits of harbor seals in the Prince
William Sound-Copper River Delta
area, Alaska. Mar. Mammal Comm.,
Washington, D.C.
Scheffer, T. H., and C. C. Sperry
1931 Food habits of the Pacific harbor
seal, Phoca richardii [sic] . J. Mammal.
12: 214-26.
Shustov, A. P.
1965 The food of ribbon seals in the Bering
Sea. Izv. TINRO 59: 178-83.
Spalding, D. J.
1964 Comparative feeding habits of the fur
seal, sea lion and harbour seal on the
British Columbia coast. Fish. Res.
Bd. Can. Bull. 146.
VanWinkle, M. E., and W. L. Schmitt
1936 Notes on the Crustacea, chiefly
Natantia, collected by Dr. Robert
A. Bartlett in arctic seas. J. Wash.
Acad. Sci. 26: 324-31.
Pruter, A. T.
1973
Rae, B. B.
1973
Development and present status of
bottomfish resources in the Bering
Sea. J. Fish. Res. Bd. Can. 30:
2373-85.
Further observations on the food of
seals. J. Zool. 169: 287-97.
Wilke, F.
1957
Food of sea otters and harbor seals
at Amchitka Island. J. Wildl. Man.
21: 241-2.
Zimushko, V. V., and S. A. Lenskaya
1970 Feeding of the gray v^^hale (Eschrich-
tius gibbosus Erx.) at foraging grounds.
Ekologiyal: 205-12.
Foods and Trophic Relationships of Cetaceans
in the Bering Sea
K. J. Frost and L. F. Lowry
Alaska Department of Fish and Game
Fairbanks
ABSTRACT
Available data on food habits of 13 species of cetaceans in
the Bering Sea are reviewed. Fin (Balaenoptera physalus),
minke (B. acutorostrata), and humpback (Megaptera nouae-
angliae) whales feed mainly on euphausiids (Thysanoessa
spp.) and pelagic and semidemersal fishes such as walleye
pollock (Theragra chalcogrammaj, herring (Clupea harengus),
and capelin (Mallotus villosus). It is not known whether bow-
head whales (Balaena mysticetus) feed in the Bering Sea in
winter. In summer in the Beaufort Sea they are known to
eat euphausiids, copepods, and other crustaceans. Gray
whales (Eschrichtius robustus) feed primarily on benthic
amphipods and to a lesser degree on epifaunal invertebrates.
Sperm (Physeter catodon) and beaked (Berardius bairdii,
Mesoplodon stejnegeri, and Ziphius cavirostris) whales and
Dall porpoises (Phocoenoides dalli) eat mostly squids and
deepwater fishes. White whales (Delphinapterus leucas)
and harbor porpoises (Phocoena phocoena) feed primarily on
pelagic and semidemersal fishes. Killer whales (Orcinus
orca) eat pelagic and semidemersal fishes and other marine
mammals.
In the Bering Sea a pelagic food web supports all cetaceans
except gray whales. Cetaceans compete for food among them-
selves and with fishes, pinnipeds, seabirds, and people. The
grey whale may consume about 1.2-3.4 percent of the avail-
able food benthos. Data needed as a basis for such estimates
for the other species are not available.
INTRODUCTION
Thirteen species of cetaceans, including eight
odontocetes and five mysticetes, occur in the Bering
Sea in significant numbers on a regular seasonal or
year-round
1977):
basis (Nishiwaki 1974, Braham et al.
Suborder Odontoceti (toothed whales and porpoises)
Physeter catodon, sperm whale
Orcinus orca, killer whale
Berardius bairdii, Baird's beaked whale
Mesoplodon stejnegeri, Stejneger's beaked whale
Ziphius cavirostris, Cuvier's beaked whale
Delphinapterus leucas, white whale
Phocoena phocoena, harbor porpoise
Phocoenoides dalli, Dall porpoise
Suborder Mysticeti (baleen whales)
Balaenoptera physalus, fin whale
Balaenoptera acutorostrata, mlnke whale
Megaptera novaeangliae, humpback whale
Eschrichtius robustus, gray whale
Balaena mysticetus, bowhead whale
Several other species occur occasionally but because
of low numbers and limited distribution they cannot
be considered ecologically significant components
of the system.
Some of the v^^hales are seasonally migratory;
others engage only in local movements. During the
winter months most baleen whales inhabit warm
waters at low latitudes, where they bear their young.
Feeding activity is greatly reduced at that time. In
the spring they migrate to cold, biologically produc-
tive high-latitude waters, where they feed intensively
825
826 Marine mammals
over the summer months. Fat reserves accumulated
during this period sustain the whales throughout the
winter in the warmer, less productive seas. The
energetic advantages of such migratory behavior
have been discussed by Brodie (1975) and Laws
(1977).
Baleen whales concentrate on feeding grounds
where prey, especially euphausiids, and copepods,
are abundant. Regions of high zooplankton abun-
dance coincide with persistent and recurrent con-
centrations of whales. The feeding grounds are
usually along boundaries between warm and cold
water masses where there is upwelling and mixing,
especially along the continental shelf slope and in
areas of convergence, in backwaters, and in the
center of areas with cyclonic movement (Nemoto
1957, Sleptsov 1961). Feeding areas may shift
within or between years as a result of changes in the
distribution or abundance of prey populations, or
both. In years when zooplankton are scarce, some
whales may seek out concentrations of pelagic
fishes.
Baleen whales feed in different ways. Although
all are basically adapted for straining small prey
from large volumes of water, they vary greatly
in the size of prey they consume as well as in the
concentrations of prey necessary to facilitate
efficient feeding. See Nemoto (1970) for a dis-
cussion of the different feeding types.
A major difference in feeding strategies exists
between baleen whales and toothed whales. Since
toothed whales feed primarily on fishes and cephalo-
pod moUusks which are abundant and accessible
throughout the year, they probably do not fast for
extended periods (Norris 1967). In general, feeding
grounds of toothed whales tend to be less distinct
than those of baleen whales, although early whalers
did report sperm whale "grounds" (Rice 1978a).
Toothed whales are often found where there are
concentrations of schooling pelagic fishes. Choice
of prey often changes as the distribution and abun-
dance of fishes change throughout the year.
Almost all the information we have on the
feeding habits of whales has been gathered in
conjunction with commercial whaling operations.
As a result, adequate data on kinds and quantities
of foods consumed are available only for those
whales which have been or are now of commercial
importance. Because whalers operate in areas
where whales are most abundant, feeding informa-
tion is likely to identify not only important prey
species but also the areas where prey are most con-
centrated. Most recent accounts of feeding habits of
whales are found in Soviet and Japanese literature
(Nemoto 1957, 1959, 1970; Tomilin 1957; Sleptsov
1961; Klumov 1963; Zimushko and Lenskaya
1970). Earlier accounts may be found in old
whaling logs and such works as Scammon (1874).
Some data on the foods of bowhead and white
whales are available from studies of stranded animals
and of the subsistence harvests of Alaskan Eskimos
(Lowry et al. 1978; Lowry and Frost, unpublished
data).
FEEDING HABITS OF CETACEANS
Fin whales
Fin whales are an oceanic species and are world-
wide in distribution. They spend the vdnter in
temperate to subtropical waters and migrate toward
the poles during the summer feeding season. Some
enter the Bering Sea and less commonly, the Chukchi
Sea (Nemoto 1957, 1959; Sleptsov 1961; Klumov
1963; Nishiwaki 1966). Fin whales are known to
migrate through and to feed in St. George, Norton,
and Hope basins. They are most abundant south of
61°N (Braham et al. 1977).
In the North Pacific the exploitable population
of fin whales is estimated at 14,000-19,000 and the
total population (including juveniles) at 21,000-
29,000 (Gambell 1976, Scheffer 1976). How many
of these whales move into the Bering Sea is un-
known; the numbers may vary from year to year
in relation to zooplankton production.
Fin whales consume pelagic crustaceans, pri-
marily euphausiids and copepods, in large quanti-
ties, along with a variety of shoaling fishes and
sometimes squids. In the Bering Sea, Thysanoessa
inermis is the most important euphausiid prey of
fin whales, as well as of most other baleen whales.
T. inermis forms extensive swarms over the conti-
nental shelf margin from July to September
(Nemoto 1959, 1970). Three other species, T.
longipes, T. spinifera, and T. raschii, also form
swarms; their importance to fin whales varies
depending on the geographic area and oceanographic
regime. These euphausiids feed mainly on phyto-
plankton and small zooplankton and are most
abundant in areas of high primary productivity.
There is a major concentration of T. inermis south-
west of the Pribilof Islands (Nemoto 1959) which
coincides with an abundance of fin whales.
Copepods of the genus Calanus are also important
foods of fin whales. Two species, C. cristatus and
C. plumchrus, are abundant north of the Aleutian
Islands, where C. plumchrus is usually the most
abundant copepod in plankton tows. Although it
is an important prey of fishes, it does not form
Cetaceans 827
dense swarms, and hence is of minor importance
to fin whales. C. cristatus is the most important
copepod prey of fin whales in the Bering Sea
(Nemoto 1957, 1959). Only the copepodite-5
stage, an immature form which is present in near-
surface waters, is eaten by fin whales. Adult C.
cristatus are found south of the shelf in waters more
than 500 m deep— deeper than the whales dive to
feed. Nemoto (1957) reported that copepodites
of C. cristatus are most abundant in near-surface
waters of the Bering Sea in spring and early summer,
when water temperatures are low; they comprise
a major part of the stomach contents of fin whales
at that time. Later in the summer, when copepods
become less abundant, euphausiids assume greater
dietary importance for these whales.
In years when euphausiids and copepods are not
abundant in the southern Bering Sea, and in aireas
farther north in the Bering and Chukchi seas (north
of 58°N), fishes are of major importance in the diet
of fin whales (Nemoto 1959, Klumov 1936). The
species of greatest importance are herring (Clupea
harengus), capelin (Mallotus uillosus), and pollock
(Theragra chalcogramma). Pollock probably are
most important at or near the shelf break. In
general, fin whales take pollock less than 30 cm
long, herring about 25 cm long, and capelin about
15 cm long (Nemoto 1959).
Fin whales also eat arctic cod (Boreogadus saida),
saffron cod (Eleginus gracilis). Pacific cod (Gadus
macrocephalus), Atka mackerel (Pleurogrammus
monopterygius), rockfish (Sebastodes spp.), smelt
(Osmerus mordax), and salmon (Oncorhynchus
spp.) (Tomilin 1957). Arctic and saffron cod are
eaten most commonly in the northern Bering Sea
(Klumov 1963).
Fin whales probably are the most polyphagous
of baleen whales. In the Bering Sea they consume
a larger number of species than in the Antarctic,
where they eat almost exclusively euphausiids
(Nemoto 1957). Their diet appears to change from
year to year and from location to location, depend-
ing on whether euphausiids, copepods, fishes, or
squids are most abundant.
Blue (Balaenoptera musculus) and sei whales
(B. borealis) sometimes occur in the southern
portion of the Bering Sea (Tomilin 1957). In
general, blue whales in the North Pacific and Bering
Sea eat primarily euphausiids, mainly Thysanoessa
inermis, and some copepods (Tomilin 1957, Nemoto
1959). According to Nemoto, in years when
euphausiids become abundant early in the season
and copepod production is poor, blue whales mi-
grate early into the Bering Sea. In other years they
wait for the euphausiid bloom.
Sei whales eat mainly Calanus copepods and
some euphausiids, fishes, and squids (Tomilin
1957). They have been reported to eat smelt, sand
lance (Ammodytes hexapterus), arctic cod, rock-
fish, greenling (Hexagrammos spp.), pollock and
capelin.
Humpback whales
Humpback whales, like fin whales, occur in both
the Southern and Northern hemispheres. Three
isolated populations exist, one in the Southern
Hemisphere and one each in the North Pacific and
North Atlantic (Wolman 1978). Unlike blue, sei,
and fin whales, they are found in shallow coastal
waters and near oceanic islands rather than in deep
ocean areas.
Humpback populations were greatly depleted by
commercial whaling during the late nineteenth and
early twentieth centuries. The pre-exploitation
North Pacific population is estimated to have been
about 15,000 (Wolman 1978). Gambell (1976)
estimated the present North Pacific population at
between 1,200 and 1,600 whales, with three main
winter concentrations: in the western Pacific
around the Mariana, Bonin, and Ryukyu islands and
Taiwan; around the Hawaiian Islands; and in Mexi-
can waters along the coast of Baja California.
Some North Pacific humpback whales spend
summer months feeding in the Gulf of Alaska,
along the Aleutian Islands, and throughout shallow
shelf waters of the Bering Sea. Some migrate as
far north as Bering Strait (Nemoto 1957, Tomilin
1957, Braham et al. 1977). Their journey north-
ward from the wintering grounds begins in March
or April, and they reach the Bering Strait and the
southern Chukchi from July to September (Tomilin
1957, Wolman 1978).
In the North Pacific, both euphausiids and fishes
are major foods of these whales (Nemoto 1957,
1959, 1970; Tomilin 1957; Klumov 1963). In the
northern part of the North Pacific, Nemoto (1957)
found only euphausiids in 201 of 261 stomachs
containing food. Fifty-six contained only fishes,
or a combination of fishes and euphausiids. Squids
were present in only two of the stomachs. South of
Nunivak Island in July, Nemoto (1978) observed
a group of humpbacks feeding on Thysanoessa
raschii. In areas west of Attu and south of Amchit-
ka, humpbacks fed almost exclusively on Atka
mackerel 15-30 cm long (Nemoto 1957, 1959);
at other sites along the Aleutians, they fed on
euphausiids and pollock (Nemoto 1978). Other
828 Marine mammals
fishes eaten by humpbacks include herring, capehn,
sand lance, smelt, cod, salmon, rockfish, saffron
cod, and arctic cod (Nemoto 1957, Tomilin 1957,
Klumov 1963). According to Klumov, humpbacks
in the Bering and Chukchi seas are found near aggre-
gations of arctic cod, herring, and capelin. Tomilin
(1957) identified mysids, Mysis oculata, as the pri-
mary prey in Bering Strait and in the southern
Chukchi Sea; pelagic amphipods (Parathemisto
libellula), shrimps (Eualus gaimardii and Pandalus
goniurus), and arctic and saffron cod were also
eaten. Klumov (1963) listed Calanus copepods as
prey, but Nemoto (1959) maintained that hump-
back whales do not ordinarily eat copepods because
of the coastal distribution of the whales and the
oceanic distribution of the copepods.
Minke whales
Minke or "little piked" whales inhabit both the
Northern and Southern hemispheres; the world-
wide population is estimated at about 325,000
(Scheffer 1976). Pacific minke whales winter at
low latitudes, between 20° and 25° N, and spend the
summer in colder, high-latitude waters (Mitchell
1975a). In summer they are found throughout the
Bering Sea and in the southern Chukchi Sea
(Sleptsov 1961, Braham et al. 1977). According to
Braham et al. (1977), they are one of the four most
commonly observed cetaceans in the Bering Sea.
Minke whales are also present in the Norton and
Hope basins. They are often found in coastal aireas,
bays, and inlets, as well as in the southern edge of
the pack ice (Tomilin 1957, Nemoto 1959).
In the North Pacific, euphausiids and shoaling
fishes are major foods of minke whales; pelagic
squids and copepods are of lesser importance
(Nemoto 1959, 1970; Klumov 1963). Among the
fishes eaten are herring, Pacific cod, pollock, Atka
mackerel, sand lance, capelin, and arctic and saffron
cod. Lowry (unpublished data) examined the
stomach of a minke stranded at Unalaska Island in
the Aleutians and found it to contain only pollock.
In the Chukchi and northern Bering seas, arctic
cod are the major forage species (Tomilin 1957,
Sleptsov 1961, Klumov 1963). Brodie (1977)
suggested that the white color pattern on the
flippers of North Pacific minke whales is a feeding
adaptation. The flashing, brilliantly white f Uppers
may startle approaching fishes, so that those neeir
the outer edges of the flippers move away from
the whale, and those nearer the center are further
concentrated toward the mouth, because the dark
head coloration makes the mouth look like an
"escape hole." In the Antarctic, where minkes
feed almost entirely on euphausiids (Nemoto
1970), white flipper coloration is uncommon.
Bowhead whales
Bowhead whales are found only in the Northern
Hemisphere. Their numbers were severely depleted
by intense commercial whaling in the North Pacific
during the late 1800's and early 1900's. Present
estimates indicate a population of 1,800-2,900
(Braham et al. 1979). It is not known where bow-
heads winter, but the southwestern Bering Sea near
the ice front may be a wintering ground (Braham
et al. 1979). In the spring they migrate northward
through the Bering Strait, passing Point Hope and
Point Barrow and then moving eastward to Canadian
waters (Amundsen Gulf and west of Banks Island),
where they spend the summer feeding. The reverse
migration occurs mainly in September and October.
It is not known whether bowhead whales feed
during the winter in the Bering Sea. Apparently
they feed very little during the northward migration,
for the stomachs of whales taken by Eskimos at
Point Hope and Point Barrow in spring are usually
empty. Food has been found in the stomachs of
some whales taken during the fall migration (Lowry
et al. 1978). Reported food items include euphau-
siids, copepods, gammarid amphipods, hyperiid
amphipods, mysids, and pteropods (MacGinitie
1955, Tomilin 1957, Lowry et al. 1978). The
presence of benthic amphipods, small snails, and
clams in stomachs indicates that bowheads some-
times feed at or near the bottom (Mitchell 1975b,
Lowry et al. 1978, Lowry, unpublished).
Gray whales
Although there was formerly a population of gray
whales in the North Atlantic (Mitchell and Mead
1977), they are now found only in the Pacific Ocean
and adjacent waters of the Arctic Ocean. Two
geographically isolated stocks exist in the North
Pacific: the Korean stock, which migrates between
South Korea and the Sea of Okhotsk, and the Cali-
fornia stock, which migrates between Baja Cali-
fornia and the Bering and Chukchi seas (Rice and
Wolman 1971).
California gray whales were once severely de-
pleted by commercial whaling, but now appear to
have been restored nearly to pre-exploitation levels.
Recent surveys give population estimates of 16,500
± 2,900 (Reilly et al. 1979). Gray whales winter in
warm coastal waters of Baja California and the
southern Gulf of California.
From late February to April they begin a north-
ward migration, following the coast closely. They
Cetaceans 829
arrive in the Bering Sea in April and May. In the
Bering and Chukchi seas, they apparently are
restricted to shallow waters (usually less than 50-60
m deep) by their feeding habits (Tomilin 1957,
Klumov 1963, Rice and Wolman 1971). From June
to October they are found mostly north of 61°
latitude and south of the edge of close pack ice
(Brahametal. 1977).
In the Bering Sea, gray whales are benthic feeders.
They eat primarily amphipods, many of them
infaunal species. Concentrations of 14,000-24,000
amphipods/m^ have been found in the southern
Chukchi Sea where gray whales feed (Zimushko
and Lenskaya 1970); among the most important
genera are Ampetisca, Anonyx, Pontoporeia
Lembos, Eusirus, and Atylus (Tomilin 1957, Pike
1962, Klumov 1963, Zimushko and Lenskaya 1970).
In addition, gray whales are known to eat poly-
chaetes, small bivalves, gastropods, ascidians, priap-
ulids, isopods, mysids, and herring (Pike 1962,
Klumov 1963, Rice and Wolman 1971). Zimushko
and Lenskaya (1970) report that a single prey
species usually made up from 80 to 90 percent
of the total stomach contents of individual whales
they examined.
In general, gray whales probably feed very little
along their migration route (Rice and Wolman
1971). Stomachs of animals taken along the Cali-
fornia coast almost invariably were empty. The few
stomachs examined from gray whales in the calving
lagoons were also empty (Scammon 1874). How-
ever, recent observations by Sund (1975), Welling-
ton and Anderson (1978), Norris (1979), and
Cunningham and Stanford (in preparation) suggest
that they may do some feeding south of the regular
feeding grounds, on small fishes, euphausiids,
mysids, and pelagic anomuran crabs.
Sperm whales
The sperm whale or cachalot is the largest of the
toothed whales. Recent estimates of numbers of
sperm whales in the North Pacific vary from
432,000 (Gambell 1976) to 774,000 (Rice 1978a).
How many of these enter the Bering Sea each year
is unknown. These whales are migratory, probably
in response to availability of prey, but they do not
alternately feed and fast like baleen whales.
The social structure of sperm whales is complex.
Herds consisting of females attended by harem bulls
are segregated from herds of bachelor bulls, which
may be immature. Females are not usually found
north of about 45°, but males are found as far north
as 65° (Sleptsov 1961, Rice 1978a). Only males are
present in the Bering Sea, most in deep waters
of the western portion, off the continental shelf,
and in the vicinity of the Aleutian Islands and
Alaska Peninsula.
Throughout the world, sperm whales eat mainly
deep-water cephalopod mollusks, especially squids
of the family Gonatidae. As many as 15 species of
cephalopods have been found in a single stomach
(Tomilin 1957). Scars inflicted by giant squid of
the genus Architeuthis, which grow to 18 m long,
have been found on sperm whales. Squids 2-10 m
long are commonly found in stomachs (Tomilin
1957, Berzin 1971). Fish are less important than
squid in the diet. Tomilin (1957) found sharks
(Order Squaliformes) and skates (Family Rajidae)
to be more important than bony fishes (Class
Osteichthyes). Sperm whales do eat such bony
fishes as salmon. Pacific saury (Cololabis saira),
pollock, grenadiers (Family Macrouridae), lancet
fishes (Family Alepisauridae), Pacific cod, Atka
mackerel, rockfish, sculpins (Family Cottidae),
and lumpsuckers (Family Cyclopteridae) (Nemoto
1957, Sleptsov 1961, Berzin 1971). They also eat
Tanner crabs (Chionoecetes spp.), king crabs (Para-
lithodes spp.), and spider crabs (Hyas spp.) in
waters 20-25 m deep (Tomilin 1957).
Sperm whales are capable of deep diving. Off
Durban, South Africa, researchers recorded an 85-
minute dive to a depth of 3,193 m. Benthic sharks
were found in the stomach of this whale (Rice
1978a). A study off South Africa using radio
telemetry showed that dives usually are about 350
m, although deeper dives are not uncommon
(Lockyer 1977). It is not clear whether the whales
usually feed at great depths or eat deep-water
creatures which migrate to the upper 200 m of
water at night (Nemoto 1957, Sleptsov 1961). In
the Antarctic, sperm whales collected at night and in
the early morning had fuller stomachs than those
taken at midday (Nemoto 1957), and Lockyer
(1977) found that dives were longer and deeper in
the evening than during the day.
Killer whales
The killer whale is a cosmopolitan species which
occurs in coastal and oceanic waters of both hemi-
spheres, but penetration into arctic and antarctic
waters is limited by sea ice. Killer whales are found
throughout the Bering Sea and the southern Chuk-
chi Sea (Tomilin 1957, Sleptsov 1961). Exten-
sive migrations in the North Pacific are indicated but
have not yet been described.
Killer whales prey on gregarious fishes and marine
mammals; they also eat squids (Tomilin 1957,
Rice 1968). According to Rice, the larger whales
830 Marine mammals
(mainly males) take the greatest number of marine
mammals. Among the fishes eaten are herring,
Pacific cod, skates, smelt, capelin, halibut (Hippo-
glossus stenolepis), sharks, salmon, and arctic cod
(Tomilin 1957, Sleptsov 1961). Marine mammals
eaten include minke, humpback, gray and white
whales; harbor and Dall porpoises; seals (Family
Phocidae); sea lions and fur seals (Family Otariidae);
sea otters (Enhydra lutris); and walruses (Odobenus
rosmarus) (Tomilin 1957, Rice 1968, Scheffer
1978). Killer whales are often numerous in areas
where prey are concentrated; however. Rice (1968)
records an exception near the Pribilof Islands,
where, although there are many fur seals, killer
whales do not congregate.
Beaked whales
Very little is known about the group of species
commonly called beaked whales (Ziphiidae), espec-
ially in the Bering Sea. At least three species are
known to occur there: Stejneger's, Cuvier's, and
Baird's beaked whales (Sleptsov 1961, Nishiwaki
1974). Baird's beaked whales are oceanic whales
found only in the North Pacific, north to the
Pribilofs and St. Matthew Island (Tomilin 1957,
Rice 1978b), and possibly in the Chukchi Sea
(Sleptsov 1961). Northward migration to the Bering
Sea probably occurs from April to May with a re-
turn to the south in October and November. Baird's
whales are apparently tolerant to cold water, for
they are known to occur among ice floes in the Sea
of Okhotsk (Sleptsov 1952 in Tomilin 1957).
Cuvier's beaked whales occur in all the world's
oceans. Mitchell (1968) concluded that their dis-
tribution was continuous from Alaska to Baja
California. Most Alaska strandings were in the
Aleutian Islands. The northernmost recorded
strandings (50°-60°N) occurred between February
and September. Stejneger's beaked whales are
found only in the North Pacific (Moore 1968). In
the Bering Sea they occur north to Bristol Bay and
the Pribilof Islands (Tomilin 1957, Rice 1978b).
Beaked whales appear to be similar to sperm
whales in their feeding habits. They make long,
deep dives, and take food in deep oceanic waters
(Nemoto 1957, Rice 1978b). The scant data which
exist indicate that all three species feed mostly on
cephalopods. Baird's beaked whales are known to
eat squids, octopus, and sometimes herring and
saffron cod (Slipp and Wilke 1953, Tomilin 1957).
In California, rays, bathypelagic fishes, and crus-
taceans have also been found in their stomachs
(Rice 1978b). Stejneger's whales have been seen
chasing schools of salmon in Japan (Tomilin 1957,
Mitchell 1975c). Tomilin also noted that scars on
their skins inflicted by cephalopods suggest that
they eat squids. Cuvier's whales eat squids (Tomilin
1957).
White whales
Belugas or white whales are widespread in arctic
and subarctic waters. Many white whales spend the
summer months in the coastal zone, frequenting
shallow bays and estuaries. Their distribution is
amphiboreal; Atlantic and Pacific populations
apparently do not mix (Tomilin 1957). The Bering
Sea stock winters in the central Bering Sea and
moves in spring to the Yukon-Kuskokwim Delta,
Norton Sound, and Kotzebue Sound and north
through the Chukchi Sea to the Beaufort Sea. There
is a resident population in Bristol Bay (Tomilin
1957, Harrison and Hall 1978) estimated at 1,000-
1,500 (Lensink 1961). The rest of the Bering Sea
white whale population is estimated to be at least
8,000 (Interagency Task Group 1978).
White whales eat primarily pelagic and semide-
mersal fishes. In addition, they eat cephalopods and
crustaceans, especially shrimps. Among the fishes
eaten are herring, salmon, saffron cod, arctic cod,
capelin, flatfishes (Family Pleuronectidae), Pacific
cod, and whitefish (Coregonus spp.) (Vladykov
1946, Tomilin 1957, Kleinenberg et al. 1964,
Sergeant 1973).
There is little published information on the foods
of white whales in Alaska. Brooks (1954, 1955)
found smelt, flatfishes, sculpins, blennies, lamprey
(Lampetra japonica), shrimps, mussels, and five
species of salmon in the stomachs he examined from
Bristol Bay white whales. The main foods were
smelt in early May and downstream migrating
fingerling salmon in late May. From the first of July
through the end of August, upstream migrating
adult salmon were the main prey. LowTy et al.
(1979) reported on the foods of white whales from
the northern Bering and southern Chukchi seas.
Whales from Norton Sound and Kotzebue Sound
had eaten mainly saffron cod. In addition, sculpins,
herring, octopus, smelt, and eelpout (Family Zoar-
cidae) were eaten at one location or both.
It is probable that the distribution of white
whales is partly determined by the distribution and
abundance of aggregating fishes such as herring,
salmon, and arctic cod. Kleinenberg et al. (1964)
and Klumov (1937) have suggested that the distribu-
tion and movements of belugas in northern waters
are coordinated primarily with those of arctic cod.
Cetaceans 831
Harbor porpoise
Harbor porpoises in the North Pacific occur from
the southern coasts of Japan and Mexico northward
throughout the Bering Sea and into the Chukchi
Sea (Tomihn 1957). They have been sighted as far
north as Point Barrow and the Mackenzie River
Delta (Hall and Bee 1954, VanBree et al. 1977).
They are generally found near the coast in waters
less than 20 m deep (Leatherwood and Reeves
1978). There are no population estimates for har-
bor porpoises in the Bering Sea.
There are few published references to the diet of
harbor porpoises. In the North Atlantic they prey
on pelagic or semidemersal fishes such as herring,
capelin, mackerel (Family Scombridae), sardines
(Family Clupeidae), cods and whiting (Family
Gadidae), and small salmonids (Family Salmonidae)
(Tomilin 1957, Rae 1973, Smith and Gaskin 1974).
Smith and Gaskin (1974), working in the Bay of
Fundy, found that the local and seasonal move-
ments of herring and of harbor porpoises were
similar. Off California and Washington, harbor
porpoises have been reported feeding on herring
(Wilke and Kenyon 1952), capelin (Scheffer 1953),
and Pacific sardines (Sardinops caerulea) (Brown
and Norris 1956). There are no published accounts
of foods of harbor porpoises in the Bering Sea.
Lowry (unpublished data) found remains of many
saffron cod 16.5-36.5 cm long in the stomach of an
animal caught in a net near Nome, Alaska, in July
1971. The stomach also contained remains of
herring and several crangonid shrimp.
Ball porpoise
Dall porpoises occur only in the North Pacific,
from Japan and California northward to the Sea of
Okhotsk and the Bering Sea (Tomilin 1957). They
are found at least as far north as Bering Strait
(Leatherwood and Reeves 1978) and may occur in
the southern Chukchi Sea (Sleptsov 1961). The
Dall porpoise is one of the four most commonly
observed cetaceans in the southern Bering Sea
(Brahametal. 1977).
Dall porpoises have been reported to eat hake
(Merluccius productus) and squid off California and
Oregon and capelin in the Gulf of Alaska (Scheffer
1953). Tomilin (1957) concluded that, although
they eat capelin, hake, and herring, their primary
food is cephalopods. Treacy (National Marine
Mammal Laboratory, Seattle, Washington, personal
communication) has examined stomach contents of
226 Dall porpoises caught by the Japanese high seas
salmon gillnet fishery in the Bering Sea and Aleutian
Islands. Most of the food consisted of squids of the
family Gonatidae. Remains of fishes and small
amounts of crustaceans (mainly shrimps and
euphausiids) also were found. Counts of otoliths
showed fishes of the family Myctophidae to account
for 91.5 percent of the total number of fishes eaten.
Sand lance, cods, and deep sea smelts (Family
Bathylagidae) each made up less than 4 percent of
the total fishes. In the Bering Strait area, Sleptsov
(1961) reported seeing Dall porpoises hunting
schools of arctic cod.
DISCUSSION
Eleven species of cetaceans regularly spend the
summer feeding in some part of the Bering Sea.
Two species, white and bowhead whales, winter
there. Although cetaceans consume a variety of
organisms in the Bering Sea, a few types of prey are
utilized by almost all species (Table 50-1). Pelagic
and semidemersal fishes are eaten by 10 of the 11
species and are a major food source of 6; no other
prey type is so widely utilized. Euphausiids are a
major food of all baleen whales except gray whales;
cephalopods, especially squids, are eaten by all
toothed whales except harbor porpoises, and by
three species of baleen whales.
All baleen whales except gray whales depend on
organisms which are part of a pelagic food web.
Some, like bowheads, depend mostly on zooplank-
ton stocks which aire seasonal and closely coupled
to primary production. Others, such as humpback,
fin, and minke whales, are generalists, feeding on
several types of prey. Because of this behavior, they
have a more diverse and reliable resource base than
if they depended entirely on organisms at a lower
trophic level, such as copepods and euphausiids.
Three species of toothed whales feed mostly
within the pelagic food web. Harbor porpoises and
white whales eat primarily pelagic fishes. During
the summer, both are coastal and often exploit
spawnning runs of capelin, herring, and smelt. Killer
whales prey on the highest trophic level of all spec-
ies: they eat not only pelagic fishes but also other
marine mammals.
Although many whales that feed pelagically
compete for the same prey, some specific differ-
ences in feeding reduce competition. Fin whales
eat pollock smaller than 30 cm, whereas humpbacks
take pollock 40-50 cm long (Nemoto 1959). Near
the Aleutians, humpbacks eat Atka mackerel, but
fin whales in the same area do not (Nemoto 1957).
Although humpbacks and minkes eat many of the
same pelagic fishes eaten by harbor and Dall por-
poises, they generally do not forage in the same
areas.
832 Marine mammals
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Within the pelagic web, cetaceans compete for
food not only with other cetaceans but also with
fishes, pinnipeds, seabirds, and people. Pollock and
other pelagic fishes may be significant competitors
of baleen whales, since both feed on copepods and
euphausiids (Bailey and Dunn 1979). Thirty to
eighty million seabirds are present in the Bering Sea
for all or part of the year (Hunt, Chapter 38, this
volume). Some— auklets, for example— eat copepods
and euphausiids in competition with fin, humpback,
and minke whales. Kittiwakes, murres, and puffins
eat large amounts of juvenile pollock, competing
with many species of whales. Hunt estimates that
1.97 X 10^ mt of food is consumed annually by
a minimum of 30 million birds. Six species of
pinnipeds also feed largely on organisms in the
pelagic food web (see Lowry and Frost, Chapter
49, this volume). Some of these compete directly
in time and space with cetaceans (e.g., fur seals, sea
lions, harbor seals, and ribbon seals). Others (ringed
seals and spotted seals) utilize the same prey, but
in winter months when most cetaceans are absent.
People harvest large quantities of finfishes in the
Bering Sea (over 2 million mt/yr in 1970-75 and
over 1 million mt in 1977 (NPFMC 1978)). The
pollock resource supports one of the largest single-
species fisheries in the world. Fisheries exist or may
soon develop for capelin, herring, smelt, and salmon.
Although most harvest of cetaceans has been
stopped or greatly reduced, people continue to af-
fect whales by competing with them for food.
In the Bering Sea, sperm and beaked whales and
Dall porpoises eat mainly deep-water squids and
fishes. These cetaceans are usually present south of
the shelf over deep water. They may feed at great
depth or close to the surface (in the upper 200 m),
depending on the location of the prey. Although
this feeding association appears quite separate from
the pelagic system, the two are closely coupled, for
the squids and deep-water fishes feed to a great
extent on euphausiids and pelagic fishes
(Akimushkin 1963).
Of the cetaceans, only the gray whale feeds
primarily on benthic organisms. Several other
species of whales occasionally eat shrimps, crabs,
mysids, etc., but none depends on the benthic food
web to the same degree as the gray whale, which
feeds mainly on epifaunal and infaunal amphipods.
Although some of the pinnipeds (e.g., bearded seals
and walruses) are benthic feeders (Lowry and
Frost, Chapter 49, this volume), none relies ex-
tensively on amphipods; however, their foraging
may have indirect effects on gray whales through
modification of benthic communities. These
Cetaceans 833
pinnipeds, as well as gray whales themselves, may
enhance the food resource of gray whales by creat-
ing disturbed habitat. Disturbance may favor
colonization by benthic amphipods such as Ampel-
isca (John Oliver, Moss Landing Marine Laborator-
ies, Calif., personal communication).
The impact of cetaceans on their food resources
in the Bering Sea is largely unknovsm, since the
estimates of population size, residence time in the
Bering Sea, body weights, consumption rates, and
prey composition are only partially knowTi for a
few species. For example, determinations by
Zimushko and Lenskaya (1970) and Rice and
Wolman (1971) indicate that the daily intake of an
average gray whale weighing 14 mt is between 1,000
and 1,200 kg of food per day. Since gray whales
are on their foraging grounds in the Bering and
Chukchi seas for at least 180 days of the year, each
whale probably consumes a minimum of 180-216
mt per year, and the whole population (15,000
whales) consumes 2.7-3.2 X 10^ mt per year. The
summer range of the California gray whale occupies
about 1 X 10^ km^ , which at a population of 15,000
whales amounts to approximately 66 km^ per whale.
The average whale would consume 2.7-3.3 g/m^ or
about 0.3 to 2.0 percent of total standing stock
(170-900 g/m^ ) of benthos. This would amount to
1.2-3.4 percent of the available "food benthos" as
defined by Alton (1974) (food benthos equals 57
percent of the total standing stock south of St.
Lawrence Island and 25 percent north of St. Law-
rence Island). Although these are only rough approx-
imations, they give some idea of the possible gross
impact of one species, the gray whale, in the north-
em Bering and southern Chukchi seas.
The data needed as a basis for such estimates for
the other species are not available.
Alton, M. S.
1974 Bering Sea benthos as a food re-
source for demersal fish populations.
In: Oceanography of the Bering
Sea, D. W. Hood and E. J. Kelley,
eds., 257-77. Inst. Mar. Sci., Occ.
Pub. No. 2, Univ. of Alaska, Fair-
banks.
Bailey, K., and J. Dunn
1979 Spring and summer foods of walleye
pollock, Theragra chalcogramma, in
the eastern Bering Sea. Fish. Bull.
77: 304-8.
Berzin, A. A.
1971
The sperm whale. Izd. Pishch.
Prom., Moskva. (Transl. from
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Braham, H. W., C. H. Fiscus, and D. J. Rugh
1977 Marine mammals of the Bering and
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Braham, H., B. Krogman, S. Leatherwood, W.
Marquette, D. Rugh, M. Tillman, J. Johnson,
and G. Carroll
1979 Preliminary report of the 1978
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Brodie, P. F.
1975 Cetacean energetics, an overview of
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1977 Form, function and energetics of
Cetacea: a discussion. In: Func-
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R. J. Harrison, ed., 3:45-58. Aca-
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Distribution and Abundance of Sea Otters
in the Eastern Bering Sea
Karl B. Schneider
Alaska Department of Fish and Game
Anchorage
ABSTRACT
The aboriginal range of the sea otter included most near-
shore waters of the eastern Bering Sea, south of the limit of
sea ice. This included southwestern Bristol Bay, the eastern
Aleutian Islands, and the Pribilof Islands. Fur hunting re-
duced sea otters in that region to a small colony near Unimak
Island and, perhaps, a few individuals in the Fox Islands.
During the past 70 years, the numbers of sea otters have in-
creased remarkably, but large areas of vacant or only partially
repopulated habitat remain.
Four separate colonies became established in the Fox and
Krenitzin islands during the 1960's. All are now growing
rapidly, but they amount to only a few hundred animals, and
most of the reproductively active animals remain concentrated
in small areas.
The remnant colony north of Unimak Island grew steadily
and expanded its range northeastward along the Alaska Penin-
sula until 1970. Extreme sea ice conditions in the early
1970's reduced the range and probably also the size of this
population. Most of the sea otters in this population now
occur between Cape Mordvinof and Cape Leontovich. They
range offshore about to the 80-m depth contour. The popu-
lation was estimated in 1976 at more than 17,000.
Small numbers of sea otters have been transplanted to the
Pribilof Islands, and a few have reached there by natural
immigration, probably from Bristol Bay. This cannot be
considered an established population, however, since reproduc-
tion has not occurred there.
Occasional sightings of sea otters in the northern Bering
Sea and Arctic Ocean are reported. These certainly represent
stray animals, since regular formation of sea ice appears to
preclude the establishment of permanent sea otter populations
in the north.
INTRODUCTION
Before European man arrived in western Alaska,
sea otters inhabited most of the nearshore waters of
the Bering Sea, south of the winter pack ice. These
included the waters around the Alaska Peninsula,
the Aleutian Islands, and the Pribilof Islands. Fur
hunting between 1742 and 1911 greatly reduced
the numbers of sea otters and completely eliminated
them from large portions of their range. Apparently
only one group survived in the eastern Bering Sea— in
the shallow waters north of Unimak Island. A few
sea otters may have survived in the Fox and Krenitzin
islands, but none remained in the Pribilof Islands.
The closest other established colonies were in the
western Aleutians and in the Sanak Islands /Sandman
Reef area.
Since 1911 sea otters have been protected by
international treaty and have steadily increased in
numbers, repopulating much of their former range.
The population in southwestern Bristol Bay has
nearly recovered, and several colonies have become
established in the Fox and Krenitzin islands. Al-
though large areas of former habitat remain vacant
or only sparsely populated, complete recovery seems
assured. Oil and gas development poses the only
serious immediate threat to full recovery.
Sea otters probably are the most vulnerable of all
marine mammals to the direct effects of oil. Unlike
most marine mammals, they have no thick, insulating
blubber layer; they rely on air trapped in their dense
fur for conservation of body heat and for buoyancy.
When clean, this fur is waterproof, and the skin over
most of the body remains dry. If the fur is soiled it
loses its insulative quality, and the animal dies of
hypothermia. Kooyman et al. (1977) demonstrated
a marked increase in the thermal conductance of
oiled pelts. Although little information is available
on the quantities and types of petroleum products
required to kill a sea otter, it appears that small
amounts of either refined fuels or crude oils will
cause death (Kenyon 1974). Kenyon (1969) cited
cases in which mass mortality of otters may have
occurred near shipwrecks.
837
838 Marine mammals
Long-term secondary effects of chronic pollution
on all species at a high trophic level are possible if
one or more of the links in the food chain are affec-
ted. Sea otters require large quantities of food (20 to
25 percent of their own body weight per day) to sup-
port their high metabolic rate. The main factor
limiting most sea otter populations appears to be
availability of food. Since sea otters feed mostly on
relatively sessile organisms, they may be exception-
ally sensitive to changes in the food chain; effects
would tend to be site-specific.
Sea otters in the eastern Bering Sea are concen-
trated now in several discrete areas. Repopulation
of former habitats depends on spreading from those
concentrations. A single oil spill could greatly reduce
or even eliminate a concentration, significantly
delaying recovery of the species. As sea otters may
be a keystone species in some areas (Estes and
Palmisano 1974), reductions in the densities of sea
otters may have a profound effect on the structure
of nearshore communities.
METHODS
Sea otter habitat extends up to 50 km offshore in
southwestern Bristol Bay. Typical shoreline surveys
proved inadequate to assess correctly the distribution
of sea otters in this area; consequently, a systematic
strip transect procedure was used in 1976 (Schneider
1976).
RESULTS AND DISCUSSION
The Bering Sea can be divided into several geo-
graphic areas, each with a different history of the
distribution and abundance of sea otters. The Kam-
chatka Peninsula, Komandorsky Islands, and Aleutian
Islands west of the Fox Islands will not be discussed
here, as sea otter populations in those areas are not
likely to be affected by activities in the eastern Bering
Sea. The remaining area can be divided into (a) the
Fox and Krenitzin islands, from Samalga Island to
Unimak Pass, (b) southwestern Bristol Bay from
Unimak Pass to Kvichak Bay, (c) the Pribilof Islands,
and (d) the northeastern Bering Sea, where sea ice
regularly occurs during the winter.
The status of sea otter populations has been
monitored since the mid-1 950's by the U.S. Fish
and Wildlife Service and the Alaska Department of
Fish and Game through periodic surveys and inci-
dental observations. In most cases, surveys consisted
of direct counts made from aircraft flown parallel
to the shoreline. Such counts, although often a poor
basis for population estimates, give a reasonable
picture of distribution and relative abundance when
visibility is good and when most sea otter habitat is
covered by the observers' effective observing radius.
Fox and Krenitzin islands
Significant sightings of sea otters in the Fox and
Krenitzin islands are presented in Table 51-1. Care
should be taken in interpreting these data because of
variable counting conditions; however, a general
trend of increase and spreading is evident. It appears
that few sea otters survived in this area at the begin-
ning of this century. By the late 1950 's, two very
small groups had become established at Samalga
(southwest Umnak Island) and Tigalda (western
Unimak Pass) islands. Individuals occasionally were
TABLE 51-1
Summary of significant sea otter sightings in the Fox and Krenitzin Islands, 1957-77 (from various USFWS reports
by Lensink and Kenyon; 1976-77 sightings made by P. Arneson during bird surveys).
1957
1960
1962
1965
1968
1969
June
1975
August 1976-
1975 1977
Ugamak
Tigalda
Avatanak
Rootok
Aiiun
Akutan
Unalga & Baby islands
Unalaska (except west end)
Umnak Pass area
Vsevidof Island area
Samalga/v/est end Umnak
North side Umnak
0
0
0
-
0
0
5
1
11
3
32
-
49
59
73
53
0
-
2
-
0
0
4
1
0
-
0
-
2
0
1
4
0
-
-
-
3
0
3
1
0
-
0
-
1
0
0
17
0
2
0
-
0
0
0
1
0
-
0
1
0
2
4
3
0
0
0
1
6
74
60
-
0
0
0
-
9
-
70
-
6
10
9
-
27
-
111
-
0
0
-
-
0
0
3
-
Sea otters 839
sighted in other areas. The Tigalda Island group
seemed to increase during the early 1960 's, but
Kenyon (1969) believed that the Samalga Island
group was barely maintaining itself.
Observations in 1969 indicated that both of those
groups were increasing and that two other concen-
trations had formed ziround Umnak Pass and Vsevidof
Island. By 1975, all four groups appeared to be
well established and were expanding their ranges.
Fig. 51-1 indicates the approximate distribution of
sea otters in this area in 1975.
By analogy with colonies of similar size in other
areas, we can assume that these groups will probably
continue to grow and expand their range. At present,
these concentrations are widely spaced, and the
majority of breeding animals remain in very limited
areas. Hence, these colonies are highly vulnerable
to local catastrophic events, such as oil spills.
Southwestern Bristol Bay
A number of fixed-wing aerial surveys of the
waters north of Unimak Island and the Alaska Penin-
sula were flown between 1957 and 1975 by U.S.
Fish and Wildlife Service and Alaska Department of
Fish and Game personnel. The most significant
counts are summarized in Table 51-2. Although
none of these surveys systematically covered the en-
tire area and the numbers of sea otters counted
varied greatly, a general pattern of change in dis-
tribution was evident.
A small population probably survived the period
of commercial exploitation in this area, remaining
in the area from near Unimak Island to Izembek
Lagoon. During the early 1960's, this remnant
expanded its range to the vicinity of Port MoUer,
although the largest numbers still remained north of
Izembek Lagoon (Kenyon 1969). By 1970, sea
otters were common as far northeast as Port Heiden,
and occasional individuals were sighted near Ugashik
and Egegik bays. In the winters of 1971, 1972, and
1974, sea ice covered this area to an unusucd extent.
Whereas it normally covers only as far as the vicinity
of Port Heiden, it advanced in those years to Unimak
Island. Many sea otters died as a result, and others
were forced south westward (Schneider and Faro
1975). The cumulative effects of three winters of
extensive ice restricted the range of this population to
the area west of Cape Leontovich. Since 1972, sea
otters occasionally have been sighted northeast of
that point, particularly near Port Moller. However,
since no breeding groups have been seen there, there
has been no evidence of major expansion of the
population into the habitat formerly occupied
northeast of Cape Leontovich since 1972 (Figs. 51-2
and 51-3).
The sea ice also reduced the numbers of sea otters.
Deaths of several hundred sea otters were recorded
in 1971 and 1972, and it is conceivable that several
thousand died in that period. The fact that the
range did not expand after the series of cold winters
suggests that the density of sea otters west of Cape
Leontovich must have been lower than in the 1960's,
when considerable range expansion occurred— a sig-
nificant reduction in numbers is implied.
Because the potential range of this population
covers more than 10,000 km^ of open water, tra-
ditional shoreline survey methods were not adequate
to estimate its size. By shoreline survey, Kenyon
(1969) estimated the population at more than 3,800
in 1965, but his survey covered only the inshore part
168°
T
166°
53^
KRENITZIN IS.
Known breeding concentrations
Frequent reports of small numbers
i
Zl
168°
166°
Figure 51-1. Sea otter distribution around the Fox and Krenitzin islands.
840 Marine mammals
of the range. In 1970, 2,157 sea otters were counted
in photographs of several pods clustered southeast of
Amak Island. One of those pods was the largest ever
recorded, containing over 1,000 sea otters. Since no
pups were visible in the photographs, all segments of
the population were not represented. The Alaska
Department of Fish and Game (1973) estimated from
aerial surveys made before 1970 that this population
contained on the order of 8,000-10,000 sea otters.
In 1976, I conducted a systematic aerial strip
transect survey of the primary sea otter range in
southwestern Bristol Bay (Schneider 1976). The
objectives of that survey were to delineate the dis-
tribution of the otters and, particularly, to identify
offshore concentration areas and to estimate the
size of the population. The results indicated that the
main range of the population extended from near
Cape Mordvinof to Cape Leontovich and included
Bechevin Bay. Izembek and Moffet lagoons were
used to a lesser extent. Small numbers may have
been present west of Cape Mordvinof, but there is
little offshore habitat for otters in that area.
Local reports indicate that small numbers of sea
otters persist near Port Moller, and that some animals
still stray as far to the northeast as Egegik. However,
those animals probably are not contributing signifi-
cantly to expansion or growth of the population. In
the absence of severe ice conditions such as those in
1971 and 1972, the population probably will expand
its range again, as its numbers increase. Hence,
consideration of the possible effects of both offshore
and onshore oil and gas exploration activities on sea
otters should include the entire potential range of the
population, extending to the Port Heiden area.
This population of sea otters was not distributed
uniformly within its range in 1976. Small areas of
extremely high density were evident, as were larger
areas of low density. I classified parts of the range as
TABLE 51-2
Significant sightings of sea otters along tiie nortii side of the Alaslca Peninsula and Unimak Island, 1957-75.
March October March May October 1972 June August
1957 1958 1962 1965 1969 1970 1971 1971 1972 1972 to June 1973 1975 1975
Cape Chichagof to
Cape Greig
Cape Greig to
Reindeer Creek
Reindeer Creek to
Cape Kutuzof
Cape Kutuzof to
Cape Lieskof
Cape Lieskof to
Moffet Point
Moffet Point to
Cape Mordvinof
Cape Mordvinof to
Cape Sarichef
Cape Sarichef to
Scotch Cap
Total
39
20
786
811 2823 482 2157
10
74
38
20
40
60
24
18
273 400-600 79
75
786 75 811 2892 482 2157 137
401
400-600 82
24 0
199 2604
0 1
0 0
223 2605
^1957-65 from USFWS reports by Kenyon and Lensink. 1975 surveys conducted under RU 67, Outer Continental Shelf
Environmental Assessment Program. None of these surveys covered the entire area. The primary purpose of this table is to
demonstrate changes in distribution and relative abundance in some areas.
Figure 51-2. Sea otter distribution north of Alaska Peninsula and Unimak Island (a) in 1957, and (b) in 1965.
841
. r^^^
170°
166"
160
156°
166
164"
156"
Figure 51-3. Distribution of sea otters north of the Alaska Peninsula and Unimak Island (a) in 1970, and (b) in 1976.
842
Sea otters 843
high, medium, or low density on the basis of the
strip count (Fig. 51-4). Observed densities averaged
6.5 sea otters/km^ in high-, 0.3/km^ in medium-, and
0.06/km^ in lov^^-density areas. Since only the sea
otters at the surface of the water were counted on
the survey, actual densities probably were higher.
The distribution shown in Fig. 51-4 is typical of
the situation on 30 and 31 July 1976; it may not be
generally typical, for somewhat different distribu-
tions have been observed in previous surveys. This
population is more mobile than those occupying
rocky coastal habitats; it disperses widely off-
shore. Whereas configurations of shoreline, offshore
islands, and rocks appear to exert strong influence on
the distribution of sea otters in most other areas,
there is relatively little relationship with those fea-
tures in this area, except in Bechevin Bay. Occa-
sionally small pods have been seen near Amak Island,
but that is not usually a high-density area. Some-
times large numbers have been concentrated near
shore; at other times low densities were found near
shore and high densities 15-30 km offshore. The
distribution on 30 and 31 July 1976 probably is
intermediate between those extremes. There ap-
peared to be two separate areas of high density,
roughly separated by a line between Amak Island and
Cold Bay. This kind of separation has been observed
in earlier surveys and may reflect varying quality of
the habitat.
Water depth seems to influence the distribution of
sea otters in southwestern Bristol Bay more than the
shoreline. Throughout much of this area, the outer
edge of high-density aireas closely conformed to the
40-m isobath, and the edge of the medium density
conformed to the 60-m isobath. Sea otters north-
east of Amak Island were distributed slightly farther
offshore, with medium densities extending to the
80-m contour in one area and high densities extend-
ing to areas 50 m deep.
Densities observed in the survey averaged 3.1 sea
otters/km^ in water 0-20 m deep, 5.8/km^ in water
20-40 m deep, 0.5/km^ in water 40-60 m deep, and
0.03/km^ in water more than 60 m deep. Only
0.84 percent of the otters counted were beyond the
60-m contour. During a survey of the area west of
Amak Island in April 1969, most of the sea otters
sighted were in water deeper than 40 m and many
were beyond the 60-m isobath. Sea otters observed
165°
55°
164°
7 —
163°
DISTRIBUTION OF SEA OTTERS
ill Low density
liil Medium density
H High density
56'
164°
163'
162'
Figure 51-4. Distribution of sea otters nortii of the Alaska Peninsula and Unimak Island, 30 and 31 July 1976.
844 Marine mammals
in deep areas were usually widely scattered; large
pods usually occurred in water less than 40 m deep.
Weather also seems to play a role in determining
offshore distribution. After severe storms, concen-
trations tended to be near shore; after several days
of calm weather animals tended to be farther offshore
and widely dispersed. The 30-31 July 1976 survey
followed a period of moderately rough weather with
winds reaching 35 kn.
Deep-water areas appear to be used for foraging
principally by adult males. Young animals and
females with pups seem to prefer shallower water.
Competition for food probably is greatest in waters
less than 40 m deep. This may limit the size of the
population, even when food in deeper water is
abundant.
The 80-m isobath is probably the outer limit of
the range of the population in the area west of Cape
Leontovich, although a few animals do stray farther.
The 80-m depth contour swings far offshore in the
vicinity of Port Moller, and hence inner Bristol Bay
has no deep water. The outer limits of potential sea
otter habitat northeast of Port Moller are unknown.
Presumably, the presence of sea ice keeps offshore
densities low throughout most of that area. Without
that limitation, much of Bristol Bay and the northern
Bering Sea could be potential sea otter habitat.
Those areas indicated as high-density in Fig. 51-4
probably should be considered as being of critical
importance to this population. Possibly the critical
area should be extended to the 30-m isobath and
include all of Bechevin Bay. This area supported
most of the population in 1970. Most reproductive
activity, rearing of young, and competition for food
occur there. Had it not been accessible in the winter
of 1972, the population probably would be virtually
extinct today. Even during the most extreme sea-ice
conditions, enough open water persisted here to allow
many healthy adult animals to survive. No such
alternative area existed to the northeast except for
smaller areas near Port Moller. The area from Cape
Leontovich to Port Moller is important for range
expansion but is not critical to the survival of the
population.
The design of the 1976 survey was chosen because
it provided good information on distribution. Un-
fortunately, it was of limited value for estimating
population size within narrow confidence limits. A
simple expansion of the counts to the entire cirea
produced an estimate of 11,681 otters. Adjustments
for diving animals and poor visibility on two transects
increased the estimate to 17,173 otters. Although
the actual number may have been somewhat higher or
lower, this probably reflects the approximate size of
the population in 1976.
There is reason to believe that both the total
population and the densities of sea otters in the area
surveyed were lower than in the 1960 's. During the
1960's, the range of the population expanded rapidly.
By 1970 substantial numbers had reached Port
Heiden, and there was evidence of expansion to the
south side of the Alaska Peninsula and Unimak
Island. Such expansion suggests that sea otter densi-
ties were higher than the available food could sup-
port. Sea-ice conditions in the early 1970 's reduced
the range of the population (Schneider and Faro
1975). Since then, former habitats to the northeast
of Cape Leontovich and to the west of Cape
Mordvinof have not been repopulated. Residents of
Cold Bay have observed that the numbers of sea
otters using Izembek Lagoon have declined (Robert
Jones, USFWS, personal communication). These
conditions suggest that competition for food, and
hence the need to expand range, has been reduced:
probably there are fewer otters.
Pribilof Islands
Sea otters were completely eliminated from the
Pribilof Islands in the late 18th or early 19th century.
Attempts to reestablish a population there through
transplants in the 1950's apparently failed, although a
few otters survived until 1961 (Kenyon 1969).
In 1968 the Alaska Department of Fish and Game
transplanted 55 sea otters to St. George Island.
Many sightings were made over the next three years,
but each year fewer groups were reported. In 1971,
A. Johnson (personal communication) counted only
three sea otters on a survey of the shoreline of St.
George Island. National Marine Fisheries Service
biologists have attempted to repeat this survey
annually in recent years. The highest count, six,
was made by R. Gentry in 1976. No pups have been
reported.
Sea otters have been sighted around St. Paul
Island on several occasions. In January 1972 an adult
male was shot there. I. Merculieff (personal com-
munication), saw one at Lincoln Bight in August of
the same year, and B. Johnson saw a single animal
at Otter Island several times in 1974. All sea otters
transplanted to the Pribilofs were tagged in a rear
flipper. The male that was shot probably was an
immigrant from Bristol Bay, for cementum layers in
his teeth indicated that he was born after the 1968
transplant, and yet he bore no evidence of having
been tagged. His skull was characteristic of Alaska
Peninsula sea otters (Roest 1973), whereas all the
transplanted animals came from Amchitka Island.
Kenyon (1969) speculated that sea otters might be
carried to the Pribilof Islands from Bristol Bay on
Sea otters 845
floating ice. All recent sightings of sea otters at St.
Paul Island occurred after the sea ice penetrated into
sea otter habitat in Bristol Bay in 1971 and 1972.
Although sea otters still exist in the Pribilof
Islands, their numbers are small, and there is no
recent evidence of reproduction. Unless further
transplants are made or immigration occurs, the
remaining population will probably die out. Immi-
gration is likely to occur periodically, and eventually
a self-sustaining population may become established.
Measures to protect the sea otters which remain
and their habitat would enhance that possibility.
Northern Bering Sea and the Arctic Ocean
Occasional sightings of sea otters at Nunivak
Island, St. Lawrence Island, Norton Sound, and even
in the Beaufort Sea (Bee and Hall 1956) have been
reported. The most recent records were of a sea otter
shot at Savoonga, St. Lawrence Island, in 1977 and
another near Deering in 1979. Similar extrahmital
occurrences have been reported in Siberia, as far
north as the East Siberian Sea (Gulin 1952, Zimushko
et al. 1968).
Although sea otters occasionally stray north of
their present range, there is no evidence that popula-
tions have ever become established north of Bristol
Bay and the Pribilof Islands.
1974 The effects of oil pollution on marine
mammals. U.S. Dep. Interior, 102
Statement Task Force B of Task
Force on Alaska Oil Development.
Proc. Rep.
Kooyman, G. L., R. W. Davis, and M. A. Castellini
1977 Thermal conductance of immersed
pinniped and sea otter pelts before
and after oiling with Prudhoe Bay
crude. In: Fate and effects of petro-
leum hydrocarbons in marine ecosys-
tems and organisms, D. A. Wolfe,
ed., 151-7. Pergamon Press, N.Y.
Roest.
A.I.
1973
Subspecies of the sea otter, Enhydra
lutris L. Los Angeles Co. Nat. Hist.
Mus. Contrib. in Science 252: 1-17.
Schneider, K. B.
1976 Distribution
and abundance of sea
otters in southwestern Bristol Bay.
In: Environmental assessment of the
Alaskan continental shelf. NOAA/
OCSEAP (Final Rep.), Quart. Rep.,
Oct. Dec. 1:469-526.
REFERENCES
Alaska Department of Fish and Game
1973 Alaska's wildlife and habitat. Anchor-
age, Alaska.
Schneider, K. B., and J. Faro
1975 Effects of sea ice on
J. Mammal. 56: 91-101.
sea otters.
Zimushko, V. V., G. A. Fedoseev, and A. P. Shustov
1968 A sea otter in the Arctic. Priroda
(Moscow) 1968: 104.
Bee, J. W., and E. R. Hall
1956 Mammals of northern Alaska. Mus.
Nat. Hist., Univ. of Kansas, Lawrence.
Estes, J. A., and J. F. Palmisano
1974 Sea otters: Their role in structuring
nearshore communities. Science 185:
1058-60.
Gulin, V.
1952 An uncommon animal in Chukotka.
Ogonek 50: 31.
Kenyon, K.
1969 The sea otter in the eastern Pacific
Ocean. U. S. Fish WUdl. Serv., N.
Amer. Fauna 68.
Northern Fur Seals in the Bering Sea
George Y. Harry and James R. Hartley
National Oceanic and Atmospheric Administration
National Marine Mammal Laboratory
Northwest and Alaska Fisheries Center
National Marine Fisheries Service
Seattle, Washington
ABSTRACT
An international treaty in 1911 prohibited the pelagic har-
vest of northern fur seals, Callorhinus ursinus, in the Bering
Sea and North Pacific Ocean, reversing the decline in abun-
dance of the Pribilof Islands herd. The herd increased in size
until the middle 1940's. Starting in 1956, measures were
taken to reduce the herd size to the assumed level of maxi-
mum sustainable yield. The expected increase in yield did not
occur— instead, there has been a substantial decline. Harvests
from the five most recent year-classes, however, have been
similar with no indication of a trend.
Fur seals begin to arrive at the Pribilof Islands in late
April, and most leave by December. Some adult males spend
the winter in the Bering Sea, but most of the herd migrates
into the Gulf of Alaska and south to waters off Washington,
Oregon, and California. In the Bering Sea fur seals feed as far
as 400 km from the Pribilof Islands.
Fur seals have a high metabolic rate and have no clear
thermal neutral zone in water less than 25 C, indicating that
the Bering Sea environment is energetically costly to these
animals. Crude-oil fouling of fur seals increases the conduc-
tance of the pelage and thereby facilitates heat loss.
Fur seals have been estimated to consume 12 to 13.5 per-
cent of their body weight per day in fish and squid in the
Bering Sea/Aleutian area. Estimates of biomass of prey con-
sumed in the Bering Sea range from 318,000 to 387,000
mt/yr. Although fur seals are thought to be opportunistic
feeders, gonatid squid, capelin (Mallotus villosus), and walleye
pollock (Theragra chalcogramma) account for over 80 percent
of the biomass consumed in the Bering Sea.
Human beings and possibly killer whales (Orcinus orca) and
large sharks kill adult fur seals. Pups are known to be con-
sumed by northern (Steller) sea lions (Eumetopias jubatus) at
St. George Island, and occasionally weakened animals are
killed and eaten by arctic foxes (Alopex lagopus).
The degree of competition between fur seals and other
species in the Bering Sea is unknown. The northern sea lion
is probably the most important direct competitor besides
people, because sea lions, abundant in the Bering Sea, consume
many of the same prey species as fur seals. The dietary and
distributional overlap with other marine mammals and seabirds
appears to be slight. Besides the commercial and subsistence
harvest of fur seals, interactions with people include sub-
stantial competition for the same fish species, incidental take
of fur seals by some fisheries, entanglement of fur seals in
fishery debris leading to injury or death, disturbance of
the animals on the Pribilof Islands, and exposure to various
contaminants in the marine environment.
INTRODUCTION
The period between 1879 and 1909 was critical
for the Pribilof Islands population of the northern
fur seal, Callorhinus ursinus, because no effective
international conservation agreement existed, and
almost a million fur seals (mostly breeding females)
were taken at sea (Johnson 1971). Between 1889
and 1909, the number taken at sea was almost twice
that harvested on land. Furthermore, many animals
killed at sea sank and were not recovered. Because
of the unrestricted kill of females in the ocean, the
number of Pribilof Islands seals declined from about
two million in 1880 to approximately 300,000 by
1911. Finally, in 1911, the four nations commer-
cially interested in fur seals, the United States, Japan,
Russia, and Great Britain (for Canada), created
the Convention for the Preservation and Protection
of Fur Seals. This international agreement prohibited
pelagic sealing by all citizens of these four countries
except aborigines using primitive methods.
In 1912, the Congress of the United States pro-
hibited commercial killing of fur seals on the Pribilof
Islands; it was not until 24 August 1917 that a com-
mercial harvest was resumed. The harvest of male
fur seals was controlled first by a quota and more
recently by season and size limits which have re-
stricted the harvest primarily to three- and four -year-
old animals. A quota was imposed on females taken
commercially from 1956 through 1968.
The prohibition against pelagic sealing and the
imposition of management practices on land reversed
the population decline. The number of fur seals
increased rapidly from 1925 until the late 1930's,
when Japan began to fear that a large fur seal herd
847
848 Marine mammals
would affect her fisheries adversely. In 1941 Japan
abrogated the existing fur seal treaty.
From 1942 until the signing of the current
convention in 1957, the Pribilof Islands herd was
protected by a provisional agreement between Canada
and the United States. No pelagic sealing took place
in the central and eastern North Pacific Ocean during
this period, although a few thousand seals were taken
annually by the Japanese in the western North
Pacific Ocean.
In the middle 1950's, representatives from Canada,
Japan, the Soviet Union, and the United States met
to negotiate a new fur seal agreement, which resulted
in the Interim Convention on Conservation of North
Pacific Fur Seals, signed in February 1957. This
agreement requires that northern fur seal populations
be brought to and maintained at the level which
will provide the greatest harvest year after year, with
due regard for the relationship of the fur seal popula-
tions to other living marine resources. The agreement
emphasizes the interaction of fur seals with other
living marine resources and orders the establishment
of an effective marine research program. As a result,
information on the biology and distribution of
northern fur seals basic to an understanding of the
Bering Sea ecosystem has been collected.
During discussions leading to the signing of the
agreement, scientists from the four nations decided
that the Pribilof Islands fur seal population had
increased beyond the level of maximum sustainable
yield. The reasons for this conclusion were that the
trend of increasing numbers of fur seals in the harvest
did not persist after the mid-1940's (Fig. 52-1), the
numbers of fur seals in the harvest varied consider-
ably, and pup mortality was high. To achieve the
100 -
90 -
80 -
I 70 -
I 60 -
I 50 -
ji
-S 40 -
S
30 -
20 -
10 -
1920 25 30 35 40 45 50 55 60 65 70 75
Year
Figure 52-1. Harvest of St. Paul Island male fur seals
1918-79.
objectives of the agreement, U.S. scientists decided to
decrease the size of the Pribilof Islands population to
the level of maximum sustainable yield (MSY) by
reducing the number of females and, hence, the
number of pups bom.
HERD REDUCTION
U.S. delegates who agreed to the 1957 fur seal
convention estimated that the number of pups from
the Pribilof Islands needed to sustain the MSY was
about 415,000. This number was calculated to
yield about 60,000 male (48,000 from St. Paul
Island) and 30,000 female (24,000 from St. Paul
Island) pelts a year (Anonymous 1955). When these
calculations were made, the average number of pups
born each year was estimated to be about 550,000.
Thus the objective of herd reduction was to decrease
the number of pups born from 550,000 to 415,000.
Later estimates of the number of Pribilof Islands
pups needed for MSY varied somewhat from
415,000. Chapman (1961) and Nagasaki (1961)
independently concluded that about 480,000 pups
were needed to produce the MSY. From this number
of pups, a sustained harvest of about 55,000 males
and 35,000 females was expected (North Pacific Fur
Seal Commission 1965). Chapman (1964) reviewed
fur seal population estimates and suggested that
pup numbers calculated from tag recoveries of the
1952-56 period were too high. He estimated that
for St. Paul Island the optimum number of pups born
was 351,000-360,000 and that in 1960-62 the average
number of pups born was 365,000. Chapman calcu-
lated that this pup production would result in a com-
mercial harvest from St. Paul Island of 40,000-45,000
males and 5,000-9,000 females. The most recent
published estimate of pup production required
for maximum sustainable yield was by Chapman
(1973), who believed that MSY would result when
about 283,000 pups were born annually on St. Paul
Island. Chapman did not present yield estimates in
his 1973 paper.
The herd reduction program began in 1956 with
the harvest of about 28,000 females. In each of the
next seven years, from 28,000 to 47,000 females
were harvested annually, except in 1960, when
only 4,000 were taken.
By 1964, since estimates of the number of pups
born indicated that the pup population was in the
lower range needed for MSY, U.S. scientists decided
that the number of females (and pups born) should
be held at about the 1963 level for several years to
obtain information on the average harvest of males
from this level of pup production. From 1964
Northern fur seals 849
\
through 1968, the annual female take was restricted
to the number calculated as exceeding losses from
natural causes. Consequently, the harvest of females
during this period was considerably reduced from
that of 1956-63.
The intentional harvest of females was stopped
after 1968, because the male harvest was not in-
creasing as expected after several years of pup pro-
duction at the 1963 level. In 1973 the commercial
harvest on St. George Island was suspended, and
efforts were made to obtain information on factors
which regulate population size. The present man-
agement policy for the herd on St. Paul Island is to
harvest only males exceeding the number required for
an adequate population of breeding males. No
females are taken. This policy is expected to allow
the St. Paul herd to reach carrying capacity.
CHANGES IN POPULATION CHARACTERISTICS
When the herd reduction began, the birth rate
was expected to increase and the death rate from
natural causes after birth to decrease, resulting in
a larger harvest. No data on birth rate are available,
but analysis of the U.S. and Canadian pelagic catch
of fur seals (for research) from 1958 to 1974 yielded
information on average age at first pupping and age-
specific pregnancy rates. Separate analyses of the
pelagic data (Kajimura et al. 1979) show neither a
substantial decrease in age at first pregnancy nor
an increase in pregnancy rates as the population was
reduced. In fact, some data suggest that among
females from four to six years old the pregnancy
rate may have declined during the period of analysis.
Lander (1979) computed survival rates of pups
on land before migration and during the first 20
months at sea for the 1950-70 year -classes. Using
these survival estimates, we find that male pup
mortality on land and for the first two years of life
decreases with fewer pups born. The decrease in
natural mortality rate of young male fur seals result-
ing from the herd reduction program did not, how-
ever, compensate for the loss of pups caused by the
killing of females. York and Hartley (1979) attribute
at least two-thirds of the loss in pup production to
the female harvest from 1956 to 1968. Thus it
appears that a larger harvest of subadult males is
possible only if a greater number of male pups are
born, presumably from a larger female population
(Fig. 52-2).
The Pribilof Islands fur seal herd has not reacted
as expected to the herd reduction program. On St.
Paul Island an average of 52,000 male fur seals was
harvested annually for the 10-year period preceding
the start of the herd reduction program in 1956.
For the 10-year period from 1970 to 1979, an aver-
age of 29,000 males was harvested yearly on this
island. The evidence does not indicate an increased
birth rate, and increased survival rates have not
overcome losses to the population resulting from
intentional herd reduction. Some of the reduced
harvest in recent years has been caused by shorter
season and smaller size limits designed to allow a
greater recruitment of males into the breeding popu-
lation. For the 1973-79 period, management regula-
tions have changed very little, and harvests from the
year-classes 1971 through 1975 have been similar,
ranging from 24,000 to 27,000 animals with no
indication of a trend.
50 r
40 -
30
20
10
>58
Pups born
.50
.53
20-22
• 56
90
120
150
50 r
40
30
20
10
Pups migrating
from land
180 210
240
• 58
. 50
.53
51 ^/^
%^^^
y^ .52
• 55
.54
•57
•2022
_L
_L
90 120 150 180
Number of pups
210
240
Figure 52-2. Yield-pup relation for male fur seals of the
1920-22 and 1950-70 year-classes from St. Paul Island
(Lander 1979). Least squares regression lines are shown
for pups bom (a = 2.341, b = 0.126) and for pups mi-
grating from land (a = 3.740, b = 0.188).
850 Marine mammals
There is no apparent explanation for the fact that
the Pribilof Islands fur seal herd did not respond as
expected to herd reduction, although evidence exists
that maximum productivity may result when the herd
size is much closer to carrying capacity than was
formerly believed necessary (Eberhardt and Siniff
1977, Fowler et al. 1978). Changes in the marine
environment, such as intensive foreign fisheries for
groundfish in the North Pacific Ocean, increased
contaminants in ocean waters, or discarded netting
and other debris in which fur seals are entangled, may
have contributed to decreased productivity of the
Pribilof Islands fur seal herd.
LIFE HISTORY
Approximately 80 percent of the northern fur
seal population breed on the Pribilof Islands and
nurse their young there. The remaining 20 percent
are from herds on the Komandorsky Islands, Robben
Island off southeastern Sakhalin Island, and some
of the Kuril Islands and a small herd which has
recently been established on San Miguel Island off
southern California.
The first animals to arrive on the Pribilof Islands
in the spring are the older bulls, which establish
territories from late April until mid -June. The oldest
females, first of the females to reach the rookeries,
arrive in June. There is a progression from older to
younger animals of both sexes as the season advances,
so that only a small proportion of yecirlings appears
on land, mostly in October and early November, and
remain only two or three weeks. Fur seals are very
site specific, especially older animals, and most return
to the rookery of birth.
Usually within a day of coming ashore, females
give birth, each to a single pup. About five days
after pupping, females are impregnated, and within
a few more days they leave the rookery to feed at
sea. They remain at sea a week or so before returning
to nurse their pups. Most pups are born during the
first three weeks in July. They are nursed for three
to four months and weaned before the adult females
begin the southward migration in November. Females
first give birth at ages four to six. From ages 8 to 13
about 90 percent of the females bear pups, and then
the pregnancy rate gradually decreases; some females
bear young at 20 or older.
Socially mature males defend their territories and
breed for about 50 days without feeding. Breeding
males are subject to high mortality and are able to
maintain a territory for only three or four seasons,
usually beginning at the age of 9 or 10.
Before the winter storms of December, most fur
seals have left the Pribilof Islands. Almost all animals
cross the Bering Sea and go through the eastern
Aleutian Islands passes into the Gulf of Alaska.
Migrating fur seals seldom approach land; they pass
mostly from 20 to 50 km offshore. Some fur seals
migrate westward into waters off Japan and mix
with animals from the Komandorsky Islands, Robben
Island, and the Kurils. The exact percentage of
Pribilof Islands fur seals that migrate to the western
Pacific is unknown but small. Wilke and Kenyon
(1954) speculated that between 1 and 5 percent of
Pribilof Islands fur seals move into Asian waters.
Taylor et al. (1955) estimated from tag returns that
about 30 percent of the three- to five-year-old fur
seals off eastern Japan had migrated from the Pribilof
Islands. Tag recoveries also demonstrated an ex-
change of immature male fur seals between the
Pribilof Islands and northwestern Pacific Islands.
Pups from the Pribilof Islands contributed an esti-
mated 12-21 percent of three- and four -year -old
males tagged from the 1958-63 year-classes and
killed on the Komandorsky Islands (North Pacific
Fur Seal Commission 1969). The PribUof Islands
have a much larger fur seal population than the
Soviet rookeries; hence, despite intermixture, less
than 1 percent of the kill on the Pribilofs comes
from other islands.
After leaving the Bering Sea, adult females and
subadults of both sexes continue their migration
south, usually singly or in pairs (Marine Mammal
Biological Laboratory 1969). Adult males appear
to remain in the more northern waters of the Gulf
of Alaska and possibly the Bering Sea, but their
winter distribution is largely unknown. Adult fe-
males occasionally migrate as far south as the border
between the United States and Mexico, but immature
animals remain farther north from California to
British Columbia (Wilke and Kenyon 1954, Kajimura
et al. 1979). Several thousand adult females are
found regularly from December to late March in the
inlets of southeastern Alaska, where they feed on
Pacific herring, Clupea harengus pallasi (Kenyon and
Wilke 1953). The northward migration begins off
California in March, and fur seals pass through the
coastal waters of Washington and British Columbia in
April, May, and June.
DISTRIBUTION IN THE BERING SEA
From 1880 until 1911, when the fur seal treaty
prohibiting pelagic sealing became effective, logbook
records of the sealing fleet provided information on
the pelagic distribution of fur seals. Townsend
(1899) summarized on a map the distribution of fur
seals from log books of 123 different vessels for
Northern fur seals 851
1883-97. Fig. 52-3 is a modification of Townsend's
map giving harvest information from the Bering Sea
and vicinity. Each circle indicates the location of a
vessel for one day's sealing. The 96-km limit (indi-
cated by a dotted line around the Pribilof Islands)
resulted from regulations which followed an 1892
treaty between the United States and Great Britain
(representing Canada). Townsend's chart indicated
that from July through September fur seals were
abundant within a semicircle as far as 250-350 km
northwest to southeast of the Pribilof Islands. This
area included deep water southeast of the 200-m
depth contour and extended southeast to the Aleu-
tian Islands. Fewer vessels operated directly north
or east of the Pribilof Islands. These sealing records
are probably a good representation of fur seal distri-
bution outside the 96-km closed area, because seal-
ing was profitable and the sealers would probably
have found other areas of concentration if they
had existed.
SIBERIA
BERING SEA
"9 '"''
a-'.
, # **«•' Umnak I.
; ^^Sk^^'-^^ '
Aleutian
\ s
\a'^
ds
1
1
es'' N
60° N
55° N
50° N
180°
W
175° W 170° W 165° W 160° W 155°
Figure 52-3. Distribution of pelagic fur seal harvest compiled by Townsend from 1883 to 1897 from log book records.
(Modified from Townsend 1899.)
852 Marine mammals
No systematic pelagic research on the distribution
of Bering Sea fur seals was carried out until 1947,
although some information was obtained incidentally
before that year. Fur seals have been seen as close
as 13 km to St. Matthew Island, but no animals
have been seen hauled out in the vicinity (Hanna
1920). Fur seals have been taken by natives of
Gambell, St. Lawrence Island (Bower 1929). The
observation farthest north in the Bering Sea was of
a large bull hauled out on Sledge Island near Nome
(Bernard 1925). Fur seal sightings have been re-
corded from the Chukchi Sea and the Arctic Ocean
off the Northwest Territories (Johnson et al. 1966).
Fur seals rarely come ashore after leaving the
Pribilof Islands unless they are sick or injured. In
the 1940's, a few hundred adults were known to
haul out on Samalga Island, a small island near the
west end of Unimak Island (Kenyon 1948). No
fur seals have been seen on Samalga Island in surveys
since 1962. Fur seals also occasionally haul out on
other islands in the Aleutian chain.
Modern pelagic fur seal investigations began in
1947. Surveys on early cruises revealed that few
animals leave the Bering Sea through western passes
of the Aleutian chain; in mid-June fur seals were
most abundant in or near Unimak Pass, apparently
moving in a thin and continuous stream of variable
density toward the Pribilof Islands (Wilke 1955).
Personnel on cruises from the Pribilof Islands east-
ward into Bristol Bay recorded no fur seal sightings
east of Amak Island, and on a westward course no
animals were sighted until the vessel was within 80
km of St. Paul Island (Wilke et al. 1958). In the
course of cruises between Unimak Pass, the Pribilof
Islands, and Unalaska, seals were found north of the
Aleutian Islands between Unimak Pass and Bogoslof
Island, along the 200-m depth contour. Distribution
along the 200-m depth contour was uneven compared
to that in the areas east of the contour, surveyed
earlier in the year. The number of seals increased in
August and remained stable through September
(Fiscusetal. 1964).
In 1963, a study of the distribution, abundance,
and feeding habits of fur seals on their summer ramge
in the Bering Sea was carried out from early July to
early September. To aid in the analysis of data, the
eastern Bering Sea (Fig. 52-4) was divided into six
major sectors centered between St. Paul and St.
George islands (Fiscus et al. 1965). The sectors were
then divided into zones. Sectors and zone numbers
were used in combination, for example, 1-7— the
first number represents the sector, the second the
zone. The shaded portion of Fig. 52-4 represents
the area surveyed in 1963. The numbers in each zone
give, from left to right: (1) the number of boat-
hunting days in the zone, (2) the total number of
seals seen, and (3) the total number of seals col-
lected. Because the zones in sector 1 were small,
they were consolidated; the numbers shown repre-
sent effort in all zones of sector 1.
In view of collecting effort, distribution of seals
in the first three zones of sectors 1 through 6 appears
uniform. Concentrations of seals were located in
1-4, 4-4, and 5-4. The most heavily used feeding
ground in 1963 was north of Cape Cheerful, Unalaska
Island. Generally, the principal movement of seals in
the Bering Sea during late summer and early fall of
1963 was between the Pribilof Islands and the feeding
grounds. Most animals appeared to travel into zone 3
and beyond in 1963 before they did any appreciable
amount of feeding. Seals foraged in almost all direc-
tions from the Pribilof Islands in 1963 (Marine
Mammal Biological Laboratory 1965a).
In 1964, during late July and again in early Sep-
tember, the known fur seal feeding grounds between
Cape Cheerful and the Akutan /Unimak Pass area of
Bering Sea were surveyed. In August, areas within
a radius of about 110 km of St. Paul Island were
surveyed. Results of the 1964 pelagic research are
given in Fig. 52-5 (Marine Mammal Biological Lab-
oratory 1965b).
An intensive survey of fur seals was carried out
from 17 July through 4 September 1974, in an area
from 8 to 57 km around the Pribilof Islands (Marine
Mammal Division 1975). Data on abundance and
distribution of fur seals in July, August, and Septem-
ber 1974 are presented in Fig. 52-6, 52-7, and 52-8,
respectively. Generally, seals were distributed more
uniformly west of the Pribilof Islands than in other
directions throughout the study period. In the far
northeastern part of the sample area density increased
from July to August.
Fig. 52-9 summarizes the fur seal sightings made
from 1958 to 1974 by the United States and Canada.
Although these data are not corrected for effort, they
give a good idea of the distribution of Pribilof Islands
fur seals in the eastern Bering Sea and eastern Pacific
Ocean. No pelagic research exclusively on fur seals
has been accomplished since 1974. During this
period, however, information on fur seal distribution
has accumulated from observations made from a
Japanese vessel engaged in research on the Dall
porpoise (Phocoenoides dalli) in 1978 and from other
vessels, usually also engaged in research on other
subjects.
Northern fur seals 853
PHYSIOLOGY AND ECOLOGICAL
RELATIONSHIPS
Kooyman et ah (1976) reported an O2 consump-
tion of 1.47 ml ml/g-hr for subadult fur seals im-
mersed in water at 6 C as controls in a study of the
effect of oil fouling on physiology. This metabolic
rate was measured over periods of activity and
inactivity. The metabolic rate tended to increase as
water temperature declined. Miller (1977) found
comparable metabolic rates in immersed subadult
fur seals and determined that there is no clear thermal
neutral zone for fur seals from 1 to 25 C. Basal
metabolic rate (BMR) was seldom reached in water
colder than 24 C, and the metabolic rate showed
a linear increase at temperatures below 20 C. In
air between 0 and 20 C, a mean O2 consumption rate
of 0.58 ml ml/g-hr was obtained for postabsorptive
resting subadult fur seals. This is assumed to be
equivalent to the BMR for subadults and is twice
the metabolic rate expected for a terrestrial mammal
of comparable size (Miller 1977).
Figure 52-4. Eastern Bering Sea. The operational area of U.S. researcii vessels is shaded. The numbers in each zone repre-
sent, from left to right, number of boat days, seals seen, and seals collected from 1 July to 5 September 1963 (Marine Mam-
mal Biological Laboratory 1965a).
854 Marine mammals
Activity levels increase along with metabolic rates
in colder water. Miller (1977) noted that fur seals
in water colder than 12 C were constantly active
and that even in water of 24 C most animals were
more active than in air. The elevated metabolic rates
and high activity levels of fur seals in water between 1
and 12 C indicate that the Bering Sea environment is
energetically costly to the animals.
Kooyman et al. (1976) studied the physiological
effect of external oil contamination on fur seals.
Their data showed a 1.5-fold increase in metabolic
rates of subadults as a consequence of crude-oil
contamination of 10 percent of the animal's surface.
This effect lasted at least two weeks. The animals
also responded behaviorally to oiling: they attempted
to remove themselves from water into the warmer air
Figure 52-5. Eastern Bering Sea. The operational area of the U.S. research vessel is shaded. The numbers in each zone
represent, from left to right, number of boat days, seals seen, and seals collected from 4 July to 8 September 1964 (Marine
Mammal Biological Laboratory 1965b).
Northern fur seals 855
during metabolic test runs, adopted an unusual
swimming position with their backs (the site of con-
tamination) arched out of the water, and seemed
reluctant to feed or enter the water after oiling.
Cleaning with either detergent or solvent did not
alleviate the metabolic effects of the oil fouling. The
fact that the thermal conductance of the subadult fur
seal pelt increased 1.7-2.0 times after crude-oil con-
tamination shows how heat is lost. Kooyman et
al. (1976) concluded that the combination of oil
contamination and the already high metabolic rates
of fur seals makes survival of oiled seals in the Bering
Sea questionable. The two- week duration of the
metabolic effect and the reluctance to feed after
contamination make survived even less likely. A
crude-oil spill in the eastern Bering Sea between May
and December could cause substantial fur seal mortal-
ity in the spill area, since the Pribilof herd is widely
scattered during those months.
From these data on metabolic rates Miller (1977)
calculated an average daily energy requirement of
4,137 kcal for a 21-kg subadult fur seal in water
at 5 C. Canadian researchers (Bigg 1979, Bigg et al.
1978) reported mean daily caloric consumption
ranging from 4,836 kcal to 9,182 kcal. These data
were obtained by calculating the mean daily caloric
content of food consumed by captive subadult fur
seals over a year. All the above data were obtained
from subadult fur seals; differences in weight, sex,
activity levels, caloric content of foods, and possibly
57-50N
57-30N
57-OON
56-30N
56-OON
55-50N
f54
155
153
152
151
150
149
148
147
146
145
171-OOW 170-OOW 169-OOW
I I ■ . I I ■ ■ I ■ ■ I ■ . I
JULY
SEALS PER HOUR
Do
□ 0.1-2.0
Q 2.1-5.0
5.1-9.9
10 or more
• Unit occupied
for less than
0.5 hour
326
325
324
323
322
321
320 319
318
317
316
315
314
313
312
311
310
309 308
307
57-50N
57-30N
57-OON
56-30N
56-OON
55-50N
171-OOW
170-OOW
169-OOW
Figure 52-6. Number of seals seen per hour of effort in each area unit occupied by a research vessel in July 1974 in the
eastern Bering Sea. The sides of each unit measure 10 minutes of latitude by 10 minutes of longitude. Units occupied for
less than 0.5 hour are marked X (Marine Mammal Division 1975).
856 Marine mammals
water temperature undoubtedly account for much of
the variation in caloric requirements.
Several authors estimate feeding rates for the
northern fur seal. In a preliminary report on food-
chain relationships of marine mammals in Alaskan
waters, Sanger (1974) assumed a consumption rate of
6 percent of body weight per day, which he charac-
terized as conservative. Bigg et al. (1977, 1978)
reported daily feeding rates of 6.7-8.5 percent for
captive adult females eating frozen Pacific herring. In
a paper on fur seal energetics. Miller (1977) summa-
rized previous estimates of feeding rates which ranged
from 6.0 to 15 percent of body weight per day and,
from his own data, estimated the feeding rate for a
subadult 21 -kg fur seal in water at 5 C as 14 percent
of body weight when the food source was walleye
pollock (Theragra chalcogramma). Since other fish
important as prey species of the fur seal have similar
caloric content and squid are only slightly lower, the
14 percent value may be considered representative for
most of the fur seal's diet. McAlister and Perez
(1977) estimated a mean effective daily consumption
rate for fur seals in the Bering Sea and Aleutians area
of 12-13.5 percent of body weight. This estimate
used Miller's consumption rate and considered the
age structure of the herd, land-sea movements during
the breeding season, and the seasonal distribution
of the fur seal population.
Using his conservative daily consumption rates
and an estimated 550,000 animals feeding from June
171-OOW
57-50N
57-30N
57-OON
56-30N
56-OON
55-50N
155
154
153
152
151
150
149
148
147
146
145
-I- ■ I I
170-OOW 169-OOW
I I ■ I ■ . I ■ ■ I ■ ■ I
I ■ ■ I
AUGUST
SEALS PER HOUR
Do
, Q 0.1-2.0
□ 2.1-5.0
^ffl R 1 — Q Q
10 or more
• Unit occupied
for less than
0.5 hour
326
325
324
323
322
321
I'll' '^
320 319
318
317
£
316
315
314
■ ' I ' ■
313
312
311
310
309 308
307
57-50N
57-30N
57-OON
56-30N
56-OON
55-50N
171-OOW
170-OOW
169-OOW
Figure 52-7. Number of seals seen per hour of effort in each area unit occupied by a research vessel in August 1974 in the
eastern Bering Sea. The sides of each unit measure 10 minutes of latitude by 10 minutes of longitude. Units occupied for less
than 0.5 hour are marked X (Marine Mammal Division 1975).
Northern fur seals 857
to November and 97,000 from December to May,
Sanger (1974) calculated the total annual food con-
sumption of fur seals in the eastern Bering Sea as
357,300 mt.
Using a higher daily consumption rate and assum-
ing a June-November feeding population of 551,000
and a December-May population of 69,000 animals,
McAlister and Perez (1977) estimated that 387,000
mt of food were consumed by fur seals in the eastern
Bering Sea. Both studies cite an estimate of between
318,000 and 340,000 mt attributed to A. Johnson
(U.S. Fish and Wildlife Service, personal communica-
tion).
The northern fur seal is a third-degree carnivore
within the schematic food chain shown in Fig. 52-10
and is second only to the northern sea lion (Eume-
topias jubatus) in the consumption of fish in the
eastern Bering Sea (McAlister and Perez 1977).
Fur seals feed almost exclusively on fish and squid.
The most important prey in the Bering Sea are fishes
of the families Gadidae (primarily walleye pollock)
and Osmeridae (primarily capelin, Mallotus villosus),
and squids of the family Gonatidae. Table 52-1
presents results of the analysis of stomach contents
of seals collected pelagically in the Bering Sea by
Canada and the United States from 1958 to 1974
from May through November (Kajimura et al. 1979).
In this analysis an index of relative importance (IRI =
percent frequency X (percent volume + percent
specimens)) is calculated in an attempt to account for
171-OOW
170-OOW
169-OOW
57-50N
57-30N
57-OON
k
56-30N
56-OON
55-50N \^^
155
ib4
153
152
151
150
149
148
147
146
145
I I I I I '"~T I ] t I I I I I I 1 1 I 1 I I I I I I I I I I I I i^
SEPTEMBER
SEALS PER HOUR
Do
f^ 0.1-2.0
2.1-5.0
■ 57-30N
5.1-9.9
10 or more
• Unit occupied
for less than
0.5 hour
■ 57-OON
326
325
324
323
322
321
320 319
318
317
£
316
315
314
313
I ' ■
312
311
310
I ' I
309 308
307
57-50N
■ 56-30N
56-OON
55-50N
171-OOW
170-OOW
169-OOW
Figure 52-8. Number of seals seen per hour of effort in each area unit occupied by a research vessel in September 1974 in
the eastern Bering Sea. The sides of each unit measure 10 minutes of latitude by 10 minutes of longitude. Units occupied for
less than 0.5 hour are marked X (Marine Mammal Division 1975).
858 Marine mammals
differences in size among prey species. In this analy-
sis, gonatid squid were the most important prey item
for the fur seal in the Bering Sea, followed by capelin
and walleye pollock. By volume, walleye pollock
predominated, accounting for 34 percent of the
volume of stomach contents cinalyzed. McAlister and
Perez (1977) present estimates of the amount of
food consumed annually by fur seals in the eastern
Bering Sea by species (Table 52-2). Pollock, capelin,
and gonatid squid combined constitute over 80 per-
cent of the total prey biomass.
The amount of predation by fur seals in the Bering
Sea fluctuates due to the seasonal migration, but
there is also evidence of a shift in prey selection
throughout the summer months when the fur seal
population is highest. Capelin are most numerous
in fur seal stomach contents in June and October;
walleye pollock predominate in July and September.
In August, pollock, the squid Berry teuthis magister,
and capelin are found in similar numbers.
As third-degree carnivores in the Bering Sea eco-
system, fur seals are themselves subject to predation.
Humans are undoubtedly the most important predator
of fur seals, as a result of the commercial harvest
of skins and small subsistence harvest allowed by
the Fur Seal Act of 1966 (16 USC 1151-1187).
Except for humans, the only known predators of
fur seals are northern sea lions, which have been
observed to consume pups in the waters just off
St. George Island, and arctic foxes (Alopex lagopus),
which occasionally kill weakened pups on the rook-
eries of both islands. In 1975 the rate of predation
by sea lions was estimated as 3-6 percent of the pup
population on St. George Island (Marine Mammal
Division 1975). It is thought that large sharks and
killer whales (Orcinus orca) prey on adult northern
176 w 172 168
1 1 1 1 1 1 1 1 1 1 1 . 1 1 1 1 1 1 1 1 1 1 1 1 1
32 128" 124" 120^
1 . 1 , 1 , 1 , 1 , 1 . 1 . 1 . 1 . 1 . 1 . 1 . 1 . 1. 1
Figure 52-9. Distribution of 68,500 fur seal sigiitings by the United States and Canada during the years 1958-74. Each
measures 1 degree of latitude by 2 degrees of longitude (Marine Mammal Division 1975).
Northern fur seals 859
fur seals, but this has never been documented (Lander
and Kajimura, in press). Rice (1968) did not report
fur seals in the stomach contents of killer whales but
confirmed that adult killer whales feed on marine
mammals, including pinnipeds.
The degree of competition for food among north-
ern fur seals, other marine mammals, and birds is
not known. Although the feeding habits and distrib-
ution of northern fur seals have been studied exten-
sively, the same cannot be said of their potential
avian and mammalian competitors in the Bering
Sea. Preliminary studies of distributions and feeding
habits do suggest which species may compete directly
with fur seals.
Seven species of pinnipeds other than the fur seal
are common in the Bering Sea. Five of these species
spend much of their life directly associated with the
ice. Of these, the bearded seal (Erignathus barbatus)
TROPHIC LEVEL
FOOD TYPE AND
REPRESENTATIVE SPECIES
1
k
PRIMARY
PRODUCERS
HERBIVORES
PRIMARY
CARNIVORES
SECONDARY
CARNIVORES
THIRD DEGREE
CARNIVORES
MICROPHYTOPLANKTON
FOURTH DEGREE
CARNIVORES
Nitzschia seriata
Coscinodiscus curvatulus
Chaetoceros spp.
ZOOPLANKTON
Smaller copepods (Calanus larvae)
Smaller copepods (Pseudocalanus sp.
Euphausiids (Thysanoessa inermis)
Amphipods (Parathemisto pacifica)
MACROZOOPLANKTON
Walleye pollock (juveniles)
Greenland turbot (juveniles)
Amphipods (Anonyx spp.)
Amphipods (Parathemisto libellula)
NEKTON
Walleye pollock
Squids (Gonatidae)
Baleen whales
Seabirds (Murres, Uria spp.)
MACRONEKTON
Northern fur seal
Turbot
True cod
FINAL CARNIVORES
Man
Killer whales
Large sharks
Figure 52-10. Simplified schematic food chain applicable to the eastern Bering Sea during summer months (June-November).
TABLE 52-1
Analysis of stomach contents of fur seals collected at sea by Canada and the United States
in the eastern Bering Sea during the combined months of May-November 1956-74.
Modified from Kajimura et al. (1979).
Food item
Frequency of
occurrence
Number Percent
Volume
CO
Percent
Index of
relative
importance
Fish:
Entosphenus tridentatus
Clupea harengus pallasi
Unidentified Salmonidae
Oncorhynchus spp.
Oncorhynchus gorbuscha
O. keta
O. nerka
Unidentified Osmeridae
Mallotus villosus
Thaleichthys pacificus
Bathylagidae
Unidentified Myctophidae
Lampanyctus sp.
Unidentified Gadidae
Gadus macrocephalus
Theragra chalcogramma
Sebastes spp.
Anoplopoma fimbria
Unidentified Hexagrammidae
Pleurogrammus monopterygius
Unidentified Cottidae
Unidentified Cyclopteridae
Aptocyclus ventricosus
Unidentified Trichodontidae
Trichodon trichodon
Ammodytes hexapterus
Unidentified Bathymasteridae
Unidentified Anarhichadidae
Anarhichas orientalis
Unidentified Pleuronectidae
Hippoglossus stenolepis
Reinhardtius hippoglossoides
Unidentified
Cephalopods:
Unidentified Squid
Unidentified Gonatidae
Gonatus sp.
Berryteuthis magister
Gonatopsis borealis
1
0.04
T*
—
—
68
2.39
90,870
7.67
19.69
19
0.67
6,252
0.53
0.38
23
0.81
9,931
0.84
0.70
1
0.04
770
0.06
—
3
0.11
7,105
0.60
0.07
2
0.07
568
0.05
—
12
0.42
1,383
0.12
0.07
548
19.29
215,441
18.17
955.63
13
0.46
1,215
0.10
0.27
200
7.04
49,103
4.14
116.23
4
0.14
37
—
—
1
0.04
10
—
—
220
7.74
47,197
3.98
96.44
6
0.21
990
0.08
0.03
468
16.47
403,941
34.08
686.30
1
0.04
270
0.02
—
5
0.18
4,262
0.36
—
2
0.07
160
0.01
—
97
3.41
22,816
1.92
7.47
2
0.07
70
0.01
—
3
0.11
132
0.01
—
2
0.07
763
0.06
—
1
0.04
120
0.01
—
1
0.04
12
—
—
30
1.06
5,641
0.48
2.00
2
0.07
133
0.01
—
4
0.14
62
0.01
—
3
0.11
538
0.05
0.04
13
0.46
550
0.05
0.04
1
0.04
2,736
0.23
—
126
4.44
11,103
0.94
10.79
217
7.64
1,706
0.14
5.04
195
6.86
12,294
1.04
26.21
,366
48.08
11,902
1.00
1,071.70
600
21.12
7,186
0.61
43.72
416
14.64
164,446
13.07
251.22
500
17.60
103,663
8.75
266.29
Total
1,185,378
100.00
*T = trace.
860
Northern fur seals 861
TABLE 52-2
Estimated amount of food consumed by northern fur seals in tiie eastern Bering Sea, by food type, based on
relative food consumption observed during June-November (1958-74). (From McAlister and Perez 1977.)
Food type
Capelin
Walleye pollock
Gonatid squid
Other Gadidae
Pacific herring
Bathylagidae
Hexagrammidae
Salmonidae
Pleuronectidae
Other Fish
Percent
of totaP
37.66
25.58
18.10
4.98
4.26
3.75
2.56
1.24
1.00
0.87
Summer
130.9
88.9
62.9
17.3
14.8
13.0
8.9
4.3
3.5
3.0
Proportionate weight of food
consumed (in thousands of mt)
Winter
14.9
10.1
7.1
2.0
1.7
1.5
1.0
0.5
0.4
0.3
Annual
145.7
99.0
70.0
19.3
16.5
14.5
9.9
4.8
3.9
3.3
Subtotal (Fish)
Subtotal (Squid)
Total
81.9
18.1
284.6
62.9
347.5
32.4
7.1
39.5
317.0
70.0
387.0
^Based on analysis of 2,914 stomachs containing food taken in the eastern Bering Sea from 1958-74 during June-November by
MMD, NMFS (N = 4,643 stomachs). Actual stomach food volume adjusted by research effort per month to obtain relative per-
centage of prey species for entire season.
and the walrus (Odobenus rosmarus) feed primarily
on benthic invertebrates, although the opportunistic
bearded seal may feed on fish also (Burns 1970;
Lowry et al. 1978; Lowry and Frost, Chapter 49, this
volume). There is almost no competition for food or
space betv^^een these two species and the fur seal. The
other ice seals, the larga seal (Phoca vitulina largha),
the ribbon seal (Phoca fasciata), and the ringed seal
(Phoca hispida), include a greater proportion of fish
in their diet. Only the larga seal and the ribbon seal
prey on fishes which are also important to the north-
ern fur seal. Lowry et al. (1978) report that walleye
pollock and capelin are key prey species for both
larga and ribbon seals in the southeastern Bering Sea.
Although a dietary overlap among ribbon seals, larga
seals, and fur seals exists, a temporal separation in
their distribution minimizes direct competition. The
ice seals are found near the Pribilof Islands only
during the winter and early spring in association with
the ice, at which time fur seals are absent (Burns
1970, Braham et al. 1977, Braham and Rugh 1978).
In the Bering Sea, besides the fur seals, there are
two species of pinnipeds not associated with ice.
The feeding habits of the harbor seal (Phoca vitulina
richardsi) are unknown in the Bering Sea, but because
this seal mainly inhabits coastal waters, it seems
unlikely to compete directly for food with fur seals
to any great extent (Braham et al. 1977). On the
other hand, the northern sea lion is probably the
most important marine mammal competitor of the
fur seal in the Bering Sea. Analysis of stomachs from
animals taken near the Aleutian Islands reveals that
northern sea lions take many of the same prey items
as fur seals in this area (Fiscus and Baines 1966).
Detailed knowledge of the distribution of northern
sea lions in the Bering Sea is lacking, but they have
been seen throughout the Bering Sea in the summer
and are known to feed between the Pribilof Islands
and the central and eastern Aleutian Islands (Kenyon
and Rice 1961, Braham et al. 1980, Fiscus and Baines
1966). During the fur seal migration, fur seals and
northern sea lions have been seen feeding together
near Unimak Pass. The present extent of the sea lion
data does not permit us to determine how much
competition there is between these two species.
However, given the large population of northern sea
lions on the Aleutian Islands, their tendency to forage
far at sea, and the commonality of prey with fur
seals, these two species may be major competitors in
the Bering Sea.
Among the toothed cetaceans found in the Bering
Sea, the Dall porpoise and the harbor porpoise
(Phocoena phocoena) may compete directly with
northern fur seals. The Dall porpoise is normally
862 Marine mammals
found in the Bering Sea south of the Pribilofs, but its
summer range may extend to the Bering Strait
(Braham et al. 1977, Leatherwood and Reeves 1978).
The harbor porpoise, a nearshore species, is found
along the Aleutian Islands and the Alaskan coastline.
Both species may prey on some fish and squid nor-
mally taken by fur seals, but the dietary overlap
appears to be slight (L. Jones, National Marine
Mammal Laboratory, personal communication). It is
unlikely that either the harbor porpoise or the Dall
porpoise is an important direct competitor of the fur
seal.
Preliminary data indicate that some avian species
may compete to some extent with fur seals for food
resources in the Bering Sea. Of species nesting on the
Pribilof Islands, the Common Murre (Uria aalge).
Thick-billed Murre (U. lomvia). Black-legged Kitti-
wake (Rissa tridactyla). Red-legged Kittiv^rake (R.
breuirostris). Homed Puffin (Fratercula corniculata),
and Tufted Puffin (Lunda cirrhata) may feed on fish
or squid species which are important to the fur seal.
The diet of kitti wakes and murres is 75 percent
fish, and because of their great biomass these species
have the most profound effects on the marine envi-
ronment near the islands (Hunt 1978; Hunt et al.
Chapter 38, this volume). Seabirds and fur seals may
take the same fish species, but it is unlikely that they
generally ingest prey of the same size. There are
so few data on the distribution and prey of seabirds
in the Bering Sea that it is impossible to assess the
degree of competition for food with fur seals.
Humans are important competitors of the northern
fur seal in the Bering Sea and elsewhere. In addition
to the harvest of fur seals on St. Paul Island, which
might more properly be considered as predation,
human beings compete for food and space with fur
seals in a variety of ways.
A primarily foreign commercial fishery for various
species has developed in the Bering Sea since 1954,
when Japan initiated its efforts (U.S. Department
of Commerce 1979). Six of the 25 species of fish
taken by fur seals are harvested commercially (Anony-
mous 1978). Some of these species, particularly
walleye pollock, are important components of the
fur seal's diet. Since 1972, catches of pollock and
other fish have declined because of catch restrictions
imposed in response to evidence of declining fish
stocks (U.S. Department of Commerce 1979). Table
52-3 compares estimates of the annual commercial
harvest of fish with estimates of annual consumption
of commercial fish species by fur seals in the Bering
Sea and Aleutian areas. The biomass estimates in
Table 52-3 are probably low, particularly for non-
commercial species (McAlister and Perez 1977).
Annually, fur seals apparently consume about 5 per-
cent of the biomass of walleye pollock in the Bering
Sea and Aleutian regions and lesser proportions of
other commercially important species.
The present effects of the commercial fisheries
on the food supply of the fur seal are not clear.
As Lander and Kajimura (in press) point out, fur
seals appear to be opportunistic feeders, and reducing
TABLE 52-3
All-nation catch data of demersal fish in the eastern Bering Sea and Aleutian regions,
1970-77, and its relationship to annual fur seal fish consumption (mt). (Modified from McAlister and Perez 1977.)
Ratio of
Estimated
fur seal annual
Average
annual
Percent
fish consumption
yearly catch
Biomass
fish
biomass
to average
(1970-76)
estimate
consumption
consumed
annual
by fur seals
by fur seals
commercial catch
Walleye pollock
1,519,639
2,426,400
118,300
4.9
0.078
Pacific cod
58,539
64,500
192
0.3
0.003
Yellowfin sole
136,984
1,634,300
-
-
-
Pacific halibut
397
30,000
528
1.8
—
Greenland turbot
70,849
126,700
3,362
2.7
0.047
Arrowtooth flounder
19,283
28,000
-
—
—
Pacific Ocean perch
35,671
—
48
—
0.001
Pacific herring
50,322
—
16,500
—
0.328
Other Species
47,658
370,934
179,840
48.5
3.774
Total Fish
1,939,343
4,680,834
317,000
0.163
Northern fur seals 863
the number of one major prey species, such as wall-
eye pollock, may or may not affect the fur seal
population. Fur seal productivity is affected by
many other conditions besides the availability of
food, such as predation, diseases, pollution, rookery
density, herd structure, and storms.
Besides reducing prey biomass, commercial fisher-
ies affect fur seals in other ways. Some seals are killed
or injured by fishing gear during commercial opera-
tions. This incidental mortality or injury, highest in
the Japanese mothership salmon fishery, is negligible
in other commercial fisheries (Anonymous 1978).
Entanglement of fur seals in net fragments and
other debris lost or discarded by the various com-
mercial fisheries undoubtedly contributes to mortal-
ity. The magnitude of mortality caused in this way
cannot be estimated by any known methods, but the
incidence of entangled seals in the commercial har-
vest increased from 1967 to a peak in 1975 and has
remained at an intermediate level to the present
(Kozloff 1979).
The effects of disturbance by managers, research-
ers, and tourists on the Pribilof Islands seals are not
well known at this time. Experiments indicate that
short-term disturbances do not prevent mothers from
providing nursing bouts of normal length (Marine
Mammal Division 1976). Before the arrival of fe-
males, territorial bulls driven off the rookery reclaim
their territories within 12 hours, apparently with
little difficulty (Marine Mammal Division 1974). No
data exist on the effects of long-term human disturb-
ance of fur seals on the rookery habitat. However,
human access to Kitovi amphitheater on St. Paul
Island has been restricted since 1975, because a
decline in the population was attributed to continued
disturbance by tourists (A. Roppel, National Marine
Mammal Laboratory, personal communication).
Except for crude-oil fouling, the effects of con-
taminants on fur seals are little known. Since fur
seals are a long-lived species feeding high on the food
chain, it is not surprising that heavy metals and
organochlorine compounds are concentrated in some
of their tissues (Anas 1974, Anas and Wilson 1970).
Organochlorine pesticides and PCB's are known to
be present in nursing pups and ingested milk (Anas
and Wilson 1974). It is not known if these contami-
nants contribute to mortality or reproductive failure,
but studies of California sea lions (Zalophus calif or-
nianus) implicate high organochlorine and PCB
residue levels in premature births (DeLong et al.
1973, Gilmartin et al. 1976).
I
I
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Seattle, Wash. Proc. Rep.
i
The Energy Cost of Free Existence
for Bering Sea Harbor and Spotted Seals
S. Ashwell-Erickson and R. Eisner
Institutes of Marine Science and Arctic Biology
University of Alaska
Fairbanks
ABSTRACT
Energy flow models based on single-prey diets were de-
veloped to assess the net energy requirements of Bering Sea
harbor (Phoca uitulina richardsi) and spotted seal (Phoca
largha) populations from long-term studies of food intake and
proximate composition, food energy content and digestibility,
and metabolic effects of temperature, feeding, exercise,
molt, and reproduction in several captive representatives of
each species. Caloric values of diets were directly propor-
tional to fat content, ranging from 0.6 to 1 percent in pollock
(Theragra chalcogramma) and from 5.1 to 18.5 percent in
herring (Clupea harengus pallasi). The mean digestible energy
of pollock and herring was 96.7 percent and 92.1 percent
of gross ingested energy, respectively, and the mean net energy
available from both diets was 80.3 percent of gross energy.
Air and water temperatures comparable to those in the natural
environment fell within the thermoneutral zone of the seals.
Basal metabolism of both seal species declined with age.
Maximum metabolic effort in water was achieved with harbor
seals carrying a weight load of 8 kg at an oxygen consumption
rate of 32.8 ml/kg -min, a value approximately four times
basal rate. Metabolism during molt in harbor seals was 83
percent of pre-molt levels. Reproductive energy costs (gesta-
tion + lactation) were estimated at 2.4 X 10^ and 2.2 X 10^
kcal/yr for individual harbor and spotted seals, respectively.
The mean annual gross energy required by both populations
combined was estimated at 5.6 X 10" kcal, corresponding to
an annual consumption of 81,600 mt of pollock, 51,700 mt of
capelin (Mallotus villosus), 37,300 mt of herring, and 46,100
mt of invertebrates, four important prey groups in the diets of
these seals. We believe these models will provide a basis for
realistic evaluation of pinniped energy requisites, once addi-
tional information on prey distribution, energy content and
digestibility, and seasonal prey preferences of seals is available.
INTRODUCTION
The seasonal ice cover of the Bering Sea shelf
provides an important substrate for pinniped rest,
reproduction, refuge, and food accessibility (Fay
1974). Sea ice covers the shelf region entirely or in
part from November through June (McRoy and
Goering 1974a) and influences productivity in all
trophic levels. The late-winter production of under-
ice microalgae occurs earlier than the spring phyto-
plankton bloom of the ice-free water column, and
may be of equal magnitude (McRoy et al. 1972,
McRoy and Goering 1974b). The substrate ice com-
munity attains peak production before the ice re-
treats, followed by a second bloom at the southern
ice front in April (McRoy and Goering 1974b).
These overlapping pulses of primary production
supply organic matter to the food chains leading to
abundant invertebrate, finfish, and mammal popula-
tions which inhabit the region. From late March to
July, large numbers of spotted seals (Phoca largha),
among others, inhabit the ice front, exploiting the
rich food supply, giving birth to young, mating,
and molting (Burns 1970, Fay 1974, Shaughnessy
and Fay 1977). From June to August or September,
harbor seals (Phoca uitulina richardsi) bear young,
mate, and renew their pelage at coastal habitats
fringing the southern Bering Sea (Burns 1970, Fay
1974, Shaughnessy and Fay 1977, Lowry et al.
1978, Pitcher and Calkins in press). The timing and
sequence (phenology) of these physical, chemical,
and biological events and their quantification are
critical to a realistic evaluation of the trophodynamic
scheme in this productive ecosystem.
PINNIPED AND FISHERY INTERACTIONS
The trophodynamic interrelationships of pinni-
ped populations and their food organisms in the
Bering Sea are not well understood. Although there
is much information on food habits and related
behavior of northern pinnipeds (Scheffer 1950;
Kenyon 1956; Wilke and Kenyon 1957; Spalding
1964; Fiscus and Baines 1966; Johnson et al. 1966;
Lowry et al. 1978, 1979; Frost et al. 1979), few
attempts have been made to define the niches occu-
pied by these mammals in the complex trophic
869
870 Marine mammals
structure of the ecosystem. Interactions between
seals and commercial fishery stocks have prompted
detailed studies of the association between marine
mammals and fisheries, such as the ecosystem model
DYNUMES being developed by the National Marine
Fisheries Service (McAlister et al. 1976; McAlister
and Perez 1977; Laevastu 1978, Laevastu and
Favorite, Chapter 37, Volume I).
Pollock are one of the major foods of harbor,
spotted, and ribbon seals (Phoca fasciata) (Lowry
et al. 1978) and are important also in the diet of
fur seals (Callorhinus ursinus) and Steller sea lions
(Eumatopias jubatus) in the Pribilof Islands airea
of the southeastern Bering Sea (Scheffer 1950,
Lowry et al. 1978). Harbor and spotted seals also
feed heavily on herring during the summer months
near shore (Lowry et al. 1978).
Overfishing has probably caused the decline of the
eastern Bering Sea pollock fishery from the peak
catch of over 1.8 X 10^ mt in 1972 to a total allow-
able catch of 9.5 X 10^ mt in 1977 (NMFS 1977).
Likewise, the herring fishery in this area has declined
steadily since the peak fishing year of 1964-65
(NMFS 1977). It has recently been estimated that
the biomass of pollock and herring consumed by
Bering Sea harbor and spotted seals exceeds the
present catch of each fishery (McAlister et al. 1976,
Lowry et al. 1978). McAlister et al. (1976) estimated
the finfish component of the total food consumed by
harbor seals, spotted seals, ringed seals (Phoca
hispida), ribbon seals, bearded seals (Erignathus
barbatus), fur seals, and sea lions in the eastern Bering
Sea to be 2-3 X 10^ mt, a figure "approximately
equivalent to, or slightly larger than" the amount
taken by the present commercial fisheries combined.
Passage of the Marine Mammal Protection Act
in 1972 and the Fishery Conservation and Manage-
ment Act in 1976 has made it clear that the Federal
Government recognizes the need to conserve and
manage marine resources. However, the two acts
also have presented conflicting policies which may
inhibit effective systems management of marine
mammal and fishery stocks in the southeastern
Bering Sea (Lowry et al. 1978). Both acts have the
management goal of maintaining optimum sustainable
populations of species, and yet management programs
for marine mammals in Alaska have not been imple-
mented and commercial fishing effort is expanding
(Lowry et al. 1978). Before adequate management
programs can be developed, knowledge of the envi-
ronmental carrying capacity of a species must be
gained from studying trophic-level relationships and
population assessment. Intensive fisheries such as
those for pollock and herring in the Bering Sea may
precipitate a "re-adjustment of marine mammal
populations" to levels significantly lower than current
ones (Lowry et al. 1978).
Present assessment of pinniped food habits and
estimates of nutritional requirements are based on
studies of both wild and captive animals. The natural
food of pinnipeds has been determined primarily
by examining stomach and intestinal contents,
feces, and vomitus, and by observing animals feeding.
Many researchers believe natural feeding to be regu-
lated mostly by circumstance, the animals tending to
exploit those species "that are most abundant,
within their geographical range, and most easily
captured and devoured" (Keyes 1968). Frequency
of feeding and daily nutritional requirements of wild
pinnipeds have not been directly determined. Daily
consumption rates ranging from 6 to 8 percent of
total body weight have been estimated for wild seals,
on the basis of calculations for captive animals
(Scheffer 1950, Sergeant 1973, Geraci 1975).
McAlister et al. (1976) assumed a daily consumption
rate of 7.5 percent of body weight in order to derive
estimates of seasonal consumption from biomass for
pinnipeds in the eastern Bering Sea. Over half of the
institutions interviewed by Hubbard (1968) fed 6-10
percent of the animal's body weight per day. Grow-
ing, pregnant, and lactating seals were given food por-
tions amounting to more than 10 percent of their
body weight (Hubbard 1968). Spalding (1964)
reviewed estimates of food requirements for captive
fur seals, sea lions, and harbor seals reported in the
literature, noting a range of 2-7 percent of body
weight consumed daily, with an average of 5 percent.
An average value of 6 percent body weight per day
was obtained when maximum weights of stomach
contents of 2-11 percent from wild specimens were
included in the data (Spalding 1964). Miller (1978)
suggested a value of 14 percent body weight as the
daily food requirement of pelagic subadult fur seals.
The great disparity in estimates reflects the general
uncertainty about food consumption rates in wild
pinnipeds and may result in unrealistic conclusions,
depending on the estimate used (Lowry et al. 1978).
Season, reproductive status, age, physical condition,
activity, and sex have been correlated with food
intake either inadequately or not at all. Values of
food consumption by captive animals, used as esti-
mates for wild pinnipeds, do not account for the
caloric contents of different diets. The diet repre-
sented by consumption figures has often been over-
looked: 7 percent may apply only to a relatively
low-fat diet such as pollock while only 5 percent may
be sufficient for caloric equivalence with a high-fat
I
Energy cost for harbor and spotted seals 871
diet such as herring (Geraci 1975). It seems clear
that, in order to appraise the impact of a pinniped
species on its prey organisms realistically, these
factors must be considered in the context of an
annual energy budget for the species.
PINNIPED BIOENERGETICS
The study of mammalian bioenergetics has had
early and wide appUcation in programs devoted to
increasing production efficiency of domestic live-
stock (Brody 1945) and, more recently, has been
directed at the evaluation of human impact on wild
populations of mammals through determining com-
mon energy sources and needs (Moen 1973). At the
organismal and populational levels, bioenergetics is
governed by the same thermodynamic principles
which dictate physical energy transfers and trans-
formations. The individual or population is repre-
sented as a thermodynamic system which exchanges
matter and energy with its surroundings, is assumed
to maintain equal rates of matter and energy influx
and efflux (a steady state), and is irreversible in that
internal work is continually converted to thermal
energy and dissipated as heat (Wiegert 1968). From
examination of energy flow in an animal, an energy
budget is derived which must be balanced and may be
extrapolated to the natural population after popula-
tion structure, stability, growth and productivity,
and energy requirements have been considered. It
is impossible to specify a continuous steady-state
condition with individual living organisms, since
growth and daily existence involve rapidly changing
thermodynamic variables. However, these transi-
tory states may be described as the establishment of
one steady state after another, integrated over time
(Gallucci 1973), or the error involved may be recog-
nized with qualification of amy conclusions derived
from energy budget calculations (Wiegert 1968).
The concept of energetic efficiency has had many
interpretations in the literature, but in studies of
trophodynamics Kozlovsky's (1968) definition seems
most appropriate. He relates ecological efficiency
to the idea of transfer efficiency, or the ratio of
energy available to trophic level n+1 to the energy
ingested or removed from trophic level n— 1 by
trophic level n. He has noted a decrease in ecological
efficiency above trophic level II (primary consumers),
"so that values below 10 percent should not be
considered anomalous." In energetics studies of a
single animal population, the gross efficiency ex-
pressed as the ratio of yield or production to inges-
tion (Slobodkin 1960) is a useful measure of ecolog-
ical efficiency.
ENERGY EXPENDITURE
In formulating the energy budget for a single
animal, whether as a means of identifying individual
variation or as a basis for extrapolation to the larger
population, the rate of energy metabolism "integrates
more aspects of animal performance than any other
physiological parameter" (Bartholomew 1977).
Measurements of whole-animal metabolism used
most frequently in energetics studies are indirect
calorimetry (measurement of oxygen consumption
and/or carbon dioxide production) and food con-
sumption trials (Gessaman 1973). The standard
measurement in indirect calorimetry is basal meta-
bolic rate (BMR), the heat production of a resting,
awake, postabsorptive (at least 12 hours fasted)
animal under thermoneutral conditions. Four major
components have been identified in metabolic studies
of captive animals: (1) the "specific dynamic action"
of food, or the energy cost of assimilation and di-
gestion (SDA); (2) the energy cost of activity; (3) the
energy cost of thermoregulation; and (4) the energy
cost of production, which includes tissue growth,
storage, and reproduction.
Levels of metabolism commonly reported in the
literature are summations of BMR and these com-
ponents (Table 53-1).
The food consumption method measures produc-
tivity in addition to metabolism. It is based on the
amount of food energy available to an animal or
trophic level, influenced by a variety of factors
related in the energy balance equation :
NE = GE - (FE + UE+ SDA) = NEp + NE„ (1)
where NE = net food energy, GE = gross food energy,
FE = fecal energy, UE = urinary energy, SDA =
specific dynamic action of food (not detectable by
the food consumption method), and NEp and NE^,
TABLE 53-1
Levels of metabolism commonly reported in the
literature. (Adapted from Gessaman 1973 and
Bartholomew 1977.)
I. Fasting Metabolism: FMR = BMR + activity
II. Resting Metabolism: RMR = BMR + SDA + thermo-
regulation
III. Maintenance Metabolism: MMR = BMR + SDA +
thermoregulation + activity
IV. Average Daily Metabolism: ADMR = BMR + SDA +
thermoregulation + activity + production
872 Marine mammals
are those components of the net food energy asso-
ciated with production and maintenance, respec-
tively. Net energy is estimated from the difference
in caloric content of food consumed (gross energy)
and material egested and excreted (feces and urine)
by a caged animal over a period of several days
(Gessaman 1973). Food is provided ad libitum and
the animal is free to move within its cage. When
NEp is measurable (the animal's body weight changes,
or it is lactating, molting, etc.), net energy is called
metabolizable energy (ME). When NEp is negUgible
(weight is constant, and other forms of production are
not occurring), and space for movement and activity
are equivalent in both food consumption and indirect
calorimetric measurements, then
NE = EM - ADMR, (2)
where EM = the energy cost of free existence
(Gessaman 1973), and ADMR = average daily meta-
bolic rate expressed as calories with use of the appro-
priate caloric equivalent of oxygen.
ECOLOGICAL EFFICIENCY IN PINNIPEDS
Much recent interest in the energetics of large
mammals has been focused on the assessment of
pinniped energy requirements in relation to natural
food resources and possible competition vdth com-
mercial fisheries (Chapman 1973, Sergeant 1973,
Boulva 1973, McAlister et al. 1976, Lavigne et al.
1977, Parsons 1977, Gallivan 1977, Miller 1978).
Ecological efficiency in pinniped populations has
most often been expressed as the gross efficiency of
production to ingestion (production /ingestion X 100)
(Sergeant 1973, Boulva 1973, Lavigne et al. 1977,
Parsons 1977). A list of comparative values of
ecological efficiency for pinnipeds and other mam-
mals from various trophic levels is presented in Table
53-2. Sergeant (1973) calculated the ecological
efficiency of northwest Atlantic harp seals at 0.5
percent, based on biomass estimates of annual pup
production and annual food intake. A higher value
of 3.9 percent for harp seals was calculated by
Lavigne et al. (1977) from estimates of 2 X BMR
for individual energy requirements, information on
population structure, caloric content of food and
seal tissue, reproductive energy requirements, and
estimates of mortality from hunting and natural
causes. They suggested that Sergeant's use of pup
production as the sole factor of yield and of biomass
approximations rather than energy values may have
resulted in an underestimate of ecological efficiency
TABLE 53-2
Values of ecological efficiency (production /ingestion X 100) for species from various trophic levels
(adapted from Lavigne et al. 1977).
Species
Ingestion
Production
Efficiency
References
Sylvilagus audubonii
(Desert cottontail rabbit)
Microtus pennsylvanicus
(Meadow vole)
Odocoileus virginianus
(White-tailed deer)
Loxodonta africanus
(African elephant)
Bos taurus
(Domestic cow)
Phoca vitulina concolor
(Atlantic harbor seal)
Phoca groenlandica
(Harp seal)
Phoca hispida
(Ringed seal)
1.08kcal/m^/yr
25.0 kcal/m^/yr
52.6 kcal/m^ /yr
71.6kcal/m^/yr
14.3 kcal/m^ /yr
7.04 X 10^ kcal/yr
0.03 kcal/m^ /yr
0.52kcal/m^/yr
0.64 kcal/m^/yr
0.34 kcal/m^/yr
0.86 kcal/m^ /yr
4.2 X 10"* kcal/yr
2.80
2.10
1.20
0.47
6.00
5.90
0.50
3.80
Chew and Chew 1970
Golley 1960
Davis and Golley 1963
Petrides et al. 1968
Petrides et al. 1968
Boulva 1973
Sergeant 1973
Parsons 1977
Energy cost for harbor and spotted seals 873
for the species. Recalculation using Sergeant's data
but with energy values increased the efficiency
estimate to 1.76 percent (Parsons 1977). Incor-
porating a stable age distribution and including
natural mortality as yield, Boulva (1973) estimated
an ecological efficiency of 5.9 percent for eastern
Canadian harbor seals, a value considered too high
by others because of overestimated caloric content
of food (Lavigne et al. 1977). Lavigne and his
colleagues repeated Boulva's calculations using
their own values for caloric content of food and
obtained an estimate of 3.5 percent. Parsons (1977)
used measurements of basal metabolic rate, digesti-
bility and caloric content of important prey items,
and estimates of energy losses from digestion and
in egested and excreted materials to estimate maxi-
mum energy requirements of captive ringed seals.
Applying this information in an analysis similar to
Boulva's, he computed an ecological efficiency of
3.8 percent for free-living Canadian Arctic ringed
seals. These values of ecological efficiency compare
favorably with estimates of 2-5 percent for mammals,
suggested by Steele (1974), and 2-3 percent for
homoiotherms (Turner 1970). In a similar study
on captive northern fur seals, Miller (1978) found
that metabolism rose in water colder than 18 C;
consequently pelagic seals had to ingest 14 percent
body weight of food per day at an average water
temperature of 5 C. He concluded that present
calculations of fur seal food consumption in the
Bering Sea and North Pacific may have been under-
estimated by a factor of two.
LIFE HISTORIES OF BERING SEA
HARBOR AND SPOTTED SEALS
Pacific harbor seals (Phoca vitulina richardsi)
and spotted or larga seals (Phoca largha) of the
Bering Sea are large populations whose annual food
consumption has been estimated at 9.7 X 10^ mt
over the eastern Bering Sea shelf (harbor and spotted
seals combined) and 3.26 X 10^ mt (harbor seals
only) in the Aleutian area (McAlister et al. 1976).
McAlister and his coworkers estimate the total
Alaskan populations of harbor and spotted seals at
2.7 X 10^ and 2.5 X 10^ respectively. They esti-
mate that approximately 6.5 X 10"* harbor seals
occupy the eastern Bering Sea shelf in summer, and
an equivalent number in winter. Harbor seals are
believed to number 8.5 X 10"* in both seasons in
the Aleutians. McAlister et al. estimate spotted
seals to number 1.25 X 10^ in summer and 2.5 X
10^ in winter in the eastern Bering Sea shelf region.
Everitt and Braham (1978) have estimated a mini-
mum abundance of 2.8-3.0 X 10"* harbor seals from
aerial censuses during the pupping season along the
northern Alaska Peninsula and eastern Aleutian
Islands from 1975 to 1977.
The harbor seal inhabits the North Pacific coast,
with numerous local breeding populations from
northwest Baja California to the Gulf of Alaska,
westward along the Aleutian and Komandorsky
Islands, and southward along eastern Kamchatka to
eastern Hokkaido (Scheffer and Slipp 1944; Fisher
1952; Bishop 1967; Marakov 1967; Belkin et al.
1969, Bigg 1969; Brownell et al. 1974; Naito and
Nishiwaki 1972, 1975). These seals occupy nearly
all inshore marine habitats along the coastal Gulf of
Alaska, Alaska Peninsula, and northern Bristol Bay,
and may occupy certain rivers and lakes in some
seasons (Lovinry et al. 1978, Pitcher and Calkins
in press). In ice-free months, they may range as far
north as Hooper Bay and the Yukon River Delta
(Lowry et al. 1978). Harbor seal pups are born
mostly on shore in June or July in the Pribilof
Islands and Bristol Bay areas (Burns 1970,
Shaughnessy and Fay 1977). Most pups are born
with a dark coat like that of adults, the white lanugo
having been shed in utero (Burns and Fay 1973, Fay
1974). Mating occurs soon after a lactation period
lasting three to six weeks (Bishop 1967, Bigg 1969,
Knutson 1974, Johnson 1976) and a short weaning
period (Johnson 1976). Mating is followed by
molting, which has been observed to last about five
weeks in captive animals (Scheffer and Slipp 1944).
Once considered a subspecies of Phoca vitulina, the
spotted or larga seal (Phoca largha) is distinguished
morphologically, ecologically, and physiologically
from the harbor seal by differential cranial charac-
teristics, its association during the breeding season
with the pack ice of the Bering, Okhotsk, Japan, and
Yellow seas, and its production of young and mating
about two months earlier (Mohr 1965; Chapskii
1967, 1969; Shaughnessy and Fay 1977). The
spotted seal's association with the ice front may be as
much a consequence of feeding behavior as of inabil-
ity to penetrate heavy ice (Fay 1974). In the Bering
Sea, pups are born in March and April on the ice with
a white, woolly lanugo (Burns 1970, Burns and Fay
1973, Burns et al. 1972, Fay 1974, Shaughnessy and
Fay 1977). The seals form widely spaced "family
groups" consisting of an adult male, a female, and a
pup, and are assumed to be territorial (Bums et al.
1972, Fay 1974). The seals disperse inshore in the
summer months; some of them migrate to the
Chukchi Sea as far as the northern coast of Alaska,
and return to the Bering ice front in the fall (Fay
1974).
874 Marine mammals
ESTIMATION OF ENERGY ASSIMILATION
A simplified budget of energy utilization in an
individual non-ruminant mammal is illustrated in
Fig. 53-1. We have attempted to quantify the various
components of this basic plan for individual captive
Bering Sea harbor and spotted seals, with the ultimate
aim of application to the wild population of each
species.
Composition, gross energy, and consumption of food
The feeding habits of harbor and spotted seals have
been reviewed by several investigators; they include
observations of feeding and analyses of gut contents
of wild specimens (Wilke 1954; Spalding 1964;
Johnson et al. 1966; Keyes 1968; Hubbard 1968;
Lowry et al. 1978, 1979). Since pollock (Theragra
chalcogramma) and herring (Clupea harengus pallasi)
were the most important finfish by volume in the
diets of these pinnipeds, they were used as food in
this particular study. The protein composition of
herring and pollock was determined by analysis of
nitrogen content in freeze-dried samples by the
Dumas method (Horwitz 1970) with an automated
nitrogen analyzer (Coleman Model 29B). Nitrogen
values were multiplied by a factor of 6.25 to yield
corresponding protein contents (Horwitz 1970).
Total lipid was extracted from freeze-dried samples
GROSS ENERGY BUDGET
GROSS ENERGY OF FOOD (GE)
APPARENT DIGESTIBLE ENERGY (DE)
METABOLIZABLE ENERGY (ME)
NET ENERGY (NE)
MAINTENANCE (NE„ )
FECAL ENERGY (FE)
URINARY ENERGY (UE)
SPECIFIC DYNAMIC
ACTION OF FOOD (SDA)
PRODUCTION (NEp)
1. BASAL METABOLISM (BMR) 1.
2. THERMOREGULATION 2.
3. ACTIVITY 3.
A. SLEEPING 4.
B. SWIMMING
C. DIVING
D. MAXIMUM WORK (Vo MAX)
ENERGY STORAGE (FAT)
GROWTH (LBM)
MOLT
REPRODUCTION
Figure 53-1. A simplified budget of energy utilization in
an individual nonruminant mammal. (Adapted from
Harris 1966, Moen 1973, Kleiber 1975.)
using a modified chloroform-methanol-water extrac-
tion technique (Bligh and Dyer 1959). The carbo-
hydrate fraction was estimated as the difference
between the total sample and the sum of the protein
and lipid fractions. The gross energy content (in
cal/g) of each food item was determined by combus-
tion of a freeze-dried sample in a bomb calorimeter
(Parr Series 1200 Adiabatic Calorimeter) according
to standardized techniques (Schneider and Flatt
1975). Nutrient composition, gross energy, and
percent moisture of these prey items are presented in
Table 53-3. In general, fishes have relatively high
proportions of protein and fat, with negligible
amounts of carbohydrate (Jacquot 1961). The ca-
loric content of prey may vary with season, age, and
location, depending primarily on the amount of
fat (Stoddard 1968).
We monitored the food intake and body weight
of eleven Pacific harbor seals and five spotted seals.
These seals were of ages 0.2-0.7 (pups), 1 (yearling),
3 (juvenile), 4 (subadult), and 9 years (adult), with
male and female representatives in all except the
yearling class. The 0.2- to 4-year-old animals were
fed Pacific herring ad libitum daily, supplemented
with vitamins and minerals (Geraci 1972a, 1972b).
Examples of food consumption, expressed as percent
body weight for a pup harbor seal and older
harbor and spotted seals are presented in Fig. 53-2.
Generally, consumption by the older seals was
highest in winter and lowest in summer, regardless
of the energy content of the food ingested. Mean
annual food consumption of one male and one fe-
male spotted seal of ages one to nine, maintained on a
diet of Atlantic mackerel (Scomber scombrus), is
shown in Fig. 53-3. Food intake declined from a
mean value of 13 percent body weight consumed
during the first year to a mean of three percent at
nine years. A curve was fitted to these data by linear
regression of log-transformed y variables, the equa-
tion of which was
y - 12.2(x + 1)-°" (r = -0.95).
N DJ FMAMJ JASONDJ FMAMJJ ASONDJ FMA
1975 h 1976 -I- 1977 -H 1978
Figure 53-2. Variation in food consumption with time
for one harbor seal pup and older harbor and spotted seals.
Energy cost for harbor and spotted seals 875
TABLE 53-3
Proximate composition and energy content of pollock and herring fed to captive pinnipeds.
Values expressed as x ± s.d.
Sample Type
Pollock
Pacific
herring
Whole
(5)
Whole
Whole
(5)
Whole
(5)
Whole
(5)
Whole
Fillet
%
H2O
%
Protein
%
Fat
% Energy content
Ash (cal/g wet) (cal/g dry) Reference
78.8 ± 1.3 19.2 ± 1.4 0.8 ± 0.2 1.6 ± 0.2 1088 ± 59 5135 ± 36 This study
76.0 ± 1.0 - - - 1408 ± 80 5868 ± 10 Miller 1978
71.7 ± 0.2 20.2 ± 1.1 5.1 ±0 2.3 ± 0.5 1564 ± 34 5498 ± 188 This study
66.8 ± 0.5 18.5 ± 0.8 12.2 ± 1.1 2.4 ± 0.1 2143 ± 75 6192 ± 57 This study
64.0 ± 0.5 16.3 ± 0.2 18.0 ± 0.5 2.0 ± 0.2 2418 + 19 6716 ± 42 This study
70.0 ± 5.1
79.4 17.5
2.6
1.2
1814 ± 201 6111 ± 370 Miller 1978
934 4382 Geraci 1975
Apparent digestible energy
In animal nutrition, the digestibility of a food or
nutrient is equivalent to the proportion absorbed in
the digestive tract (Schneider and Flatt 1975). In this
study digestibility of pollock and herring was deter-
mined in one- and four-year-old harbor seals during
separate 10-day feeding trials with a labeling tech-
nique using ^'CrClg (Mautz 1971, Miller 1978). A
solution of ^' CrCla in distUled water at a concentra-
tion of 0.6 /jCi/ml was uniformly injected into
16
14
12
10
■g 8
Phoca largha
0 o
f I
10
Figure 53-3. Mean annual food consumption of two
spotted seals from ages 1-9 years.
herring and pollock at the level of 1 ml /1 00 g fish.
Samples of feces and of treated fishes were analyzed
in a gamma spectrometer (Searle Analytic Inc.,
Automatic Gamma System, Model 1195). Percent
digestibility (DE) was calculated from the relation
[''Cr] feces - ["Cr] food /[''Cr] feces X 100% = DE
(3)
after a stable ratio was obtained of labeled feces to
labeled fish ingested. Table 53-4 lists percent digesti-
bility of pollock and herring diets in the harbor
seals, compared to results in two other species of
pinnipeds. The digestibility of herring was the same
in all the harbor seals tested, but significantly differ-
ent (P <0.05) from that of pollock in the four-year-
old seals. There were no significant differences in
digestibility of either food between sexes of seals.
Metabolizable energy, specific dynamic action,
and net energy of food
Animals lose a portion of their digestible food
energy through the production and excretion of
nitrogenous wastes in urine. Urinary energy loss
depends on the dietary protein balance and health
of the animal (Brody 1945). MetaboUzable energy
is gross food energy less fecal and urinary energy
(see Equation 1). When metaboUzable energy is
corrected for protein retention during growth (posi-
tive nitrogen balance) or protein loss during starva-
tion (negative nitrogen balance), it becomes MEn,
876 Marine mammals
TABLE 53-4
Apparent digestibility of herring and pollock diets in three pinniped species.
Species
Age
(yrs)
Food item
Apparent digestibility
(% Gross Energy)
Reference
Pacific harbor seal
1
Herring
1
Herring
4
Herring
4
Herring
4
Pollock
4
Pollock
Northern fur seal
Subadult
Herring
Subadult
Herring
Subadult
Herring
Subadult
Pollock
Ringed seal
Adult
Herring
Adult
Herring
Adult
Herring
Adult
Herring
90.6 ±
0.7
This study
91.1 ±
0.5
This study
91.4 ±
0.1
This study
91.7 ±
0.7
This study
96.6 ±
0.2
This study
96.8 ±
0.2
This study
93.0
Miller 1978
93.0
Miller 1978
93.0
Miller 1978
90.0
Miller 1978
96.9
Parsons 1977
96.2
Parsons 1977
96.3
Parsons 1977
97.9
Parsons 1977
a more exact determination of the energy available
for transformation by an animal (Maynard et al.
1979). The correction factor 7.45, determined in
studies of dogs by Rubner in 1885, has been widely
used in mammalian studies because more specific data
are lacking. During positive nitrogen balance, 7.45
kcal/g of nitrogen stored is added to the urinary
energy, resulting in a lower value of ME. During
negative nitrogen balance, 7.45 kcal/g of nitrogen
lost is subtracted from the urinary energy, causing
an increase in ME. Table 53-5 presents the results
of nitrogen balance trials performed on yearling and
four-year-old harbor seals fed maintenance rations
of herring and pollock.
The increase after ingestion of food in the meta-
bolic rate of a resting animal which has been fasting
is referred to as the "specific dynamic action" (SDA)
or "calorigenic effect" (Kleiber 1975) of food. SDA
depends on the amount and nutrient composition
of food consumed by an animal (Hoch 1971). In
terms of the energy content of food ingested, SDA
in the dog is about 6 percent for sucrose, 13 percent
for hpids, and 30 percent for proteins (Bartholomew
1977). In the mammals that have been examined,
carbohydrates increased basal metabolism by 4-30
percent for 2-5 hours after ingestion, lipids from
4 to 15 percent for 7-9 hours, and proteins 30-70
percent for as long as 12 hours (Hoch 1971). Mixed
diets of protein, fat, and carbohydrate produce lower
SDA values than those predicted from the individual
components (Forbes and Swift 1944). The elevation
of metabolic rate has been correlated with an increase
in the excretion of urinary nitrogen after intake of
amino acid, suggesting that deamination and urea
formation may account for the SDA (Buttery and
Annison 1973). The SDA per unit of food, particu-
larly protein, varies with the amount of nutrient
taken, and with the age and condition of the animal
(Brody 1945). Growing, non-lactating, and underfed
animals exhibit lower SDA values than older, lactat-
ing, or healthier animals on the same diet, because the
nutrients are largely stored and not catabolized.
Specific dynamic action of different quantities
of herring fed to yearling harbor seals was estimated
from measurements of oxygen uptake in air at ther-
moneutral conditions in temperature-controlled
rooms using an open-flow system with a paramag-
netic oxygen analyzer (Beckman Model F3) and
recorder output (Hewlett-Packard Model 7100B).
Pre- and post-prandial oxygen consumption were
calculated according to the equation of Depocas
and Hart (1957) for sections of the recorded output
exhibiting quiet behavior and steady oxygen uptake
for a minimum of 15 minutes. Fig. 53-4 illustrates
the effect of increasing food quantity (plane of
nutrition) and sleep behavior on the magnitude and
duration of post-prandial metabolic rate (SDA).
The percentage of increase in metabohsm over pre-
Energy cost for harbor and spoiled seals 877
prandial levels was calculated by comparing oxygen
consumption interpreted over time intervals equal in
duration and behavior for both conditions.
In general, the magnitude and duration of SDA
increased vdth increasing quantity of herring fed,
although sleep tended to depress the overall metabo-
lism (Benedict 1938, Hoch 1971, Swan 1974). In
the only SDA test in which a seal remained resting
and awake, the measured SDA of 28.2 percent
BMR for 10 hours was in close agreement with 30.9
percent BMR for 12-13 hours obtained for adult
ringed seals on a herring diet (Parsons 1977) and
30 percent BMR for dogs on a raw meat diet (Brody
1945, Hoch 1971, Kleiber 1975). Since the percent
elevation of BMR by SDA also depends on the size
of the animal, SDA is better expressed in terms of
the energy content of the food ingested (Kleiber
1975, Bartholomew 1977). The measured 28.2
percent elevation in basal metabolism corresponds
to a value of 177.0 kcal for the 10-hour period,
which is equivalent to approximately 5.5 percent of
the metabolizable energy and 4.7 percent of the
gross energy of the food ingested by the seal. As the
number and duration of sleep episodes increased,
metabolism was depressed to the extent that a
smaller ration fed to a seal which was awake had a
greater SDA than a larger ration fed to an animal
which slept a great deal. Lacking data for SDA of
different diets and food portions larger than mainte-
nance levels, we assume that 292.9 cal/g dry herring
(derived from the dry weight of food fed and corres-
ponding increase in metabolism over basal) was a
reasonable estimate of the SDA component in the
energy budgets of subadult and adult seals on herring
and pollock diets.
Nitrogen -corrected metabolizable energy (ME^ ),
less the specific dynamic action of food (SDA),
yields net energy (NE), or that portion of the
ingested energy available for maintenance and pro-
duction. Table 53-6 lists values for energy budget
components UE (urinary energy), FE (fecal energy),
ME (metabolizable energy), ME^ (nitrogen-corrected
metabolizable energy), SDA (specific dynamic ac-
tion), and NE (net energy) for seals in this study
and others.
ESTIMATION OF NET ENERGY COMPONENTS
That part of the net ingested energy available to a
mammal for BMR, thermoregulation, sleep, and
various activities is termed maintenance energy
(NEm ). In pinnipeds, maintenance energy require-
ments from resting and active states at different
temperatures have been estimated mainly from oxy-
gen uptake experiments.
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— BMR
J
10
HOURS POST-PRANDIAL
Figure 53-4. The effect of increasing food quantity (herring) and sleep behavior on the magnitude and duration of post-
prandial metabolic rate in four yearling harbor seals. The dashed line indicates basal metabolic rate (BMR).
878
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880 Marine mammals
Production energy (NEp ) is that component of
the net food energy which is used in forming new
body tissues (lean tissue in body growth and hair
replacement during molt), energy reserves (fat), and
reproduction (formation of gametes, production of
young and milk). Postnatal body growth, body fat
production, and the molting process have been exam-
ined to some extent in pinnipeds, while the energy
requirements of reproductive effort have only been
hypothesized.
Thermoregulation and basal metabolism
Resting heat production is sufficient to maintain
thermal homeostasis under most temperature condi-
tions encountered by a terrestrial mammal in its
natural environment (Scholander et al. 1950). The
same appears to be true for most pinnipeds that have
been studied (Irving 1973).
Most measurements of resting metabolic rate in
pinnipeds have yielded values greater than those pre-
dicted by Kleiber's (1975) equation for terrestrial
mammals, which relates daily metabolic rate in kcal
to 70 times the 3/4 power of body weight in kilo-
grams. As in growing mammals (Kleiber 1975),
newborn and nursing seals have exhibited the highest
resting metabolic rates— more than four times the
predicted mammalian values (Davydov and Makarova
1964, Eisner et al. 1977). Rates in seals several
days to several months old were 1.5 to 2.3 times the
predicted values (Irving and Hart 1957, Hart and
Irving 1959, Miller and Irving 1975, Miller et al.
1976, Eisner et al. 1977, Heath et al. 1977). Rates
approaching Kleiber's (1975) values for terrestrial
mammals have been obtained from adult seals
(Matsuura and Whittow 1973, Q)ritsland and Ronald
1975, Gallivan 1977, Parsons 1977), and an apparent
decrease in metabolic rate with increasing age and
size has been noted (Qritsland and Ronald 1975).
In the present study, oxygen consumption was
measured in animals of each age group at representa-
tive environmental air and water temperatures in all
seasons, using an open-flow system in temperature-
controlled rooms. The dates, numbers of seals tested,
body weights and ages, and the air and water temper-
atures of each experimental set are summarized in
Table 56-7. The animals were in a postabsorptive
state (12-20 hours after feeding) and were allowed to
dry completely in order to minimize evaporative
heat loss before being tested in air.
Oxygen consumption values for 0.2-3-year-old
seals at rest in air and in water at temperatures
compairable with those in the natural environment in
the Bering Sea (Zenkevitch 1963) ranged from 8.0
to 8.7 ml Og/kg-min in more than 50 replicate
TABLE 53-7
Metabolic tests in air and water on five age-groups of harbor and spotted seals.
Year
Temperature (C)
Age
(yrs)
Number
tested
Mean body
Season
Air
Water
weight (kg)
Spring
0
+4
1.0
1
36.0
0
+4
3.0
2
42.7
Summer
-t-20
+10
0.2
6
17.8
+20
+10
1.0
1
38.6
+20
+10
3.0
2
47.8
Fall
0
+4
0.3-0.5
8
21.1
0
+4
1.0
1
38.6
0
+4
3.0
2
47.8
Winter
-20
-1.8
0.7
6
28.5
-20
-1.8
1.0
1
46.3
-20
-1.8
3.0
2
49.8
Spring
0
+4
4.0
2
50.8
—
+16
9.0
2
72.3
1977
1977
1977
1977
1978
1978
Fall
4.0
46.9
Energy cost for harbor and spotted seals 881
I
I
I
I
experiments. Mean resting oxygen consumption
values for 0.2-0. 7-, 1-, and 3-year-old seals were
8.6, 8.3, and 8.4 ml O2 /kg -min, respectively. The
values of oxygen uptake in all three age groups at
rest were essentially the same at all air and water
temperatures tested and were in agreement with
basal metabolic rates obtained for young harbor
seals in air and in water by previous workers (Miller
and Irving 1975, Miller et al. 1976). Hence, we
assume that the environmental temperatures were all
within the thermoneutral zone of the seals. Also,
since these metabolic values were obtained from
resting, postabsorptive animals, apparently at ther-
moneutrality, they were considered to be basal rates.
The mean respiratory quotient for the experiments
was 0.75, with a range of 0.71-0.78.
A plot of BMR versus age is presented in Fig. 53-5,
which includes the data of Miller and Irving (1975)
and Miller et al. (1976) from Bering Sea harbor
seals younger than five weeks. Metabolic rate de-
creased rapidly from the age of two weeks to approx-
imately two months, possibly as a consequence of
improved insulation resulting from deposition of
subcutaneous fat after birth (Eisner et al. 1977).
Oxygen consumption remained relatively stable over
a period of less rapid body growth up to the age of
four, approaching the age of sexual maturity for
female harbor seals (Bishop 1967, Pitcher and Calkins
in press). For male seals, this metabolic plateau may
persist or decline more gradually in the fifth or sixth
year, the approximate age of sexual maturity in the
male (Bishop 1967, Pitcher 1977, Pitcher and Calkins
in press). In older seals, the metabolic rate decreases
from ages six to nine, the approximate age range of
physical maturity in harbor and spotted seals (Naito
and Nishiwaki 1972, Pitcher and Calkins in press). A
similar metabolic decline has been observed in humans
and other mammals from puberty to old age (Kleiber
1975, Denckla 1970).
Metabolism during sleep and normal activity
The oxygen consumption of sleeping pinnipeds,
whether hauled out or submerged, indicates a reduc-
tion of metabolic rate similar in magnitude to that
seen during quiet diving (Miller and Irving 1975,
Miller et al. 1976). The depression of deep body
temperature during sleep in pinnipeds (Bartholomew
and Wilke 1956, Irving et al. 1962, Bartholomew
1954, Miller and Irving 1975) also suggests metaboHc
decline. Sleeping seals frequently become apneic
(Bartholomew 1954, Kooyman et al. 1973). The
cardiovascular and metabolic responses associated
with apnea and diving have been noted by Irving
(1939), Scholander (1962), and Lin et al. (1972).
The metabolic economy afforded by such responses
may be of great adaptive value to a mammal with a
characteristically high resting metabolic rate (Irving
1973).
The suggestion that seals experience a reduction
of aerobic metabolism during prolonged dives arose
from early observations that quietly diving seals
did not repay their "oxygen debt" upon recovery
(Scholander 1940), and both peripheral and deep
body temperatures were lowered (Scholander et al.
1942). Scholander et al. (1942) estimated the
degree of metabolic decline in diving harbor seals
to be as much as 50-60 percent of pre-dive levels,
basing this estimate on body temperature measure-
ments and knowledge of oxygen consumption before
and after diving. Kooyman et al. (1973) reported
reduced oxygen consumption during long deep dives
by an adult Weddell seal.
In this study, oxygen consumption during sleep
and in vairious states of physical activity was meas-
ured, in addition to BMR. These results, together
with those from other pertinent studies, are pre-
sented in Table 53-8. Three levels of sleep were
identified which were metabolically the same in
air and in water: Level 1, light sleep or doze, lasting
from 1 to 15 minutes, from which animals were
easily awakened and during which metabolism was
depressed to 85 percent of BMR; Level 2, sleep
lasting from 10 to 60 minutes with metabolism equal
to 75 percent of BMR; and Level 3, heavy or deep
sleep lasting several hours with metabolism at 64
percent of BMR. Five levels of activity were defined
by characteristic behavior with relatively stable levels
of metabolism: Level 1, alert (looking, moving
head); Level 2, agonistic behavior (pawing, lunging,
biting); Level 3, vigorous surface swimming; Level 4,
13
.
Phoca vitulina richardsi •
12
P. largha o
11
-
10
•
9
8
7
6
5
-
#k
~~~-~--__
-Q- ~
4
-
3
-
2
1
1
1 1 1
1 1 1 ..J
4 5
AGE (years)
Figure 53-5. Variation of mean basal metabolic rate in
relation to age of Bering Sea harbor and spotted seals.
Curve was fitted by eye.
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882 Marine mammals
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Energy cost for harbor and spotted seals 883
quiet diving; and Level 5, exploratory diving with
underwater swimming.
Metabolism during exercise
Very few studies have been conducted on the
energy cost of exercise in pinnipeds. Maximal meta-
bolic effort has not been measured in any marine
mammal. Costello and Whittow (1975) measured
an initial increase in oxygen uptake of swimming
California sea lions, followed by a decrease to resting
levels after 60 seconds of sustained activity. Wekstein
and Krog (1971) measured an increase in metab-
olism of 1.2 times the resting rate in a yearling harp
seal permitted to swim freely in a tank. An increase
in oxygen consumption of 1.8 times resting levels
was noted by Q)ritsland and Ronald (1975) in a
swimming harp seal.
We trained three young harbor seals to carry in-
creasing workloads (provided in a weighted canvas
jacket) while treading water in a cylindrical tank
connected to an open-flow system as previously
described. The results of these experiments are
shown in Fig. 53-6. The value of maximal oxygen
uptake was attained after 5-10 minutes of exercise
and was essentially the same in all three animals
(32.8 ml Oi/kgmin) with equal workloads (8 kg).
The metabolic scope, or range of metabolic increase
from basal to maximal levels (aerobic capacity),
was equivalent to 4BMR, which is considerably
lower than corresponding values measured for other
mammals such as the dog and man (15-20BMR)
(Hoch 1971, Astrand and Rodahl 1970, Bartholomew
1977). This may conceivably be a consequence of
r
0.8 1.6 2.4 3.2 4.0 4.8 5.6 6.4 7.2 8.0
WORK LOAD IN WATER (Kgl
Figure 53-6. Plot of oxygen consumption versus work
load in water for two thermoneutral, postabsorptive young
harbor seals treading water in an exercise tank.
the high BMR of pinnipeds in general (Irving 1973,
Bartholomew 1977). Metabolic scope provides a
framework within which levels of activity metabolism
(muscular work) may be placed in proper perspec-
tive in an energy budget.
Postnatal growth of lean tissue and
accumulation of body fat
The postnatal grov^i;h curves of harbor and spotted
seals are comparable to those of most terrestrial
mammals in that they exhibit a steep initial increase
in body size or self-accelerating growth phase fol-
lowed by a gradual or self-inhibiting growth phase
(Brody 1945, Laws 1959).
Postnatal growth has been examined in Pacific
harbor seals from several locations in the northern
Gulf of Alaska (Bishop 1967, Pitcher 1977, Pitcher
and Calkins in press), Aleutian Ridge, and Pribilof
Islands (Burns and Goltsev, in preparation). In
general, males and females gain weight rapidly from
birth to the age of 5 or 6, and then more slowly up
to about 10 years of age. Males are generally longer
and heavier than adult females of the same age.
Linear growth for both sexes is rapid from birth to
4 or 5 years of age, after which it slows until physical
maturity is attained at the age of 7. The mean age
of first ovulation in female harbor seals is 5 years,
and the age of reproductive maturity (age of first
successful pregnancy) is estimated at 5.5 years.
Burns and Goltsev (in preparation) have reported
an increase in body size of Pacific harbor seals pro-
gressing westward from the Aleutians to the Pribilof
and Komandorsky islands and a similar pattern has
been observed in Gulf of Alaska harbor seals pro-
gressing from Yakutat Bay to the Alaska Peninsula
(Pitcher and Calkins in press). Fig. 53-7 presents
mean weight/age data for approximately 155 harbor
seals collected at the Aleutian, Komandorsky, and
Pribilof islands by Bums and Goltsev (in preparation).
These data have been separated into two growth
phases described by the regression equations W = 33.3
.oast
(r = 0.97) and W - 118.5-127.6 e
-0J8t
(r
— 0.98) for age-classes 0-4 and 5-24, respectively.
Postnatal growth in spotted seals has been studied
in populations of the Bering Sea (Tikhomirov 1971)
and waters around Hokkaido (Naito and Nishiwaki
1972). In general, the two sexes grow at similar rates
until 5 years of age, the female attaining sexual
maturity (first ovulation) at approximately 4 years
and the male at about 5 years. Physical maturity in
Bering Sea specimens was reported at 8 years in the
female and 9 years in the male (Tikhomirov 1971).
According to Naito and Nishiwaki (1972), females
of the Hokkaido population continued to grow until
884 Marine mammals
10-11 years and males until 14-15 years, the approxi-
mate age ranges for physical maturity.
In addition to age-related growth, seasonal changes
in body fatness of pinnipeds are well documented.
Rapid blubber accumulation from birth to weaning
has been observed in Pacific harbor seals in the Gulf
of Alaska (Bishop 1967) as well as in British Colum-
bia (Fisher 1952, Bigg 1969). The seasonal changes
of blubber thickness in adult harbor seals of the
northern Gulf of Alaska were measured by Pitcher
and Calkins (in press), who reported high, stable
levels of body fat from November to mid-May,
followed by a marked decrease during the summer
months. The lowest levels were recorded from mid-
July to mid-September, when most seals were molt-
ing. Females were consistently fatter than males, and
showed greater decreases in blubber thickness in
summer, attributable to the combined effects of
lactation, breeding, and molting. Pitcher (1977)
suggested a sequence of fat depletion in harbor seals
of Prince William Sound, beginning with the rapid
decline in lactating females, followed by that in
breeding males, and ending in a decline in immature
seals of both sexes during the molt.
Body weights of five age-classes of seals were
monitored continuously during this study. The
quantity of body fat during the spring and fall in seals
0.3, 1, 3, and 4 years of age was determined indirect-
ly by the tritiated water method (HoUeman and
Dieterich 1973). Two hours after injection of 10
/iCi/kg of tritiated water, blood samples were ob-
tained by catheter from the intra vertebral extradural
vein in restrained animals. The samples were vacuum-
distilled, and aliquots were prepared from the dis-
tillate for counting in a liquid scintillation system
140 1-
( Nuclear Chicago Mark I). Total body water was
calculated according to the method of HoUeman and
Dieterich (1973), and lean body mass was computed
as the quotient of total body water and the factor
0.73, which represents the proportion of water by
weight in a lean mammal (Pace and Rathbun 1945).
Fat was computed as the difference between total
body weight and lean body mass.
Total body weights of two harbor and spotted seals
are plotted against time in Fig. 53-8, with the propor-
tions of lean body mass (LBM) and body fat indi-
cated. Body fat content appears to vary with sea-
sonal variation of food intake, while total body
weight and lean body mass increase.
Mean annual body weight of two spotted seals
from 1 to 9 years of age is plotted in Fig. 53-9. The
elevated food intake of these seals from 1 to 3 years
(see Fig. 53-3) corresponds to the steady increase in
body weight (body growth) during that period.
These growth data are in close agreement with growth
information (length /age) obtained by Tikhomirov
(1971) for Bering Sea spotted seals and are described
by the regression equation W = 17.3 e°"^'"' (r = 0.95)
over the range of 0-3 years of age.
Molt
The annual shedding of hair in phocine seals occurs
soon after the mating season, and since the seals
appear to remain out of the water for much of its
duration (McLaren 1958, Sergeant 1973, Frost et
al. 1979, Johnson and Johnson 1979), they probably
feed infrequently (McLaren 1958, Hart and Fisher
1964, Johnson et al. 1966, Mansfield 1967, Hubbard
1968, Spalding 1964, Goltsev 1971). Observations of
wild and captive seals suggest that the shedding
period may last as long as five weeks (Scheffer and
Slipp 1944), and that it takes place first in young and
Phoca vitulina richardsl o
P. largha %
8ix.
.^-ifFAT
AGE (years)
Figure 53-7. Postnatal growth (weight/age) of harbor
seals from the Aleutian Ridge and Pribilof Islands, Alaska.
II I I I I I I ] r I I I I I I I I I I I I I I
NDJFMAMJ JASONDJ FMAMJJASONDJFMAMJ JA
1975 (- 1976 H- 1977 H- 1978
Figure 53-8. Variation in total body weight, lean body
mass (LBM), and body fat with time for one harbor and
one spotted seal.
Energy cost for harbor and spotted seals 885
Phoca largha
J I I L
J L
4 5 6
AGE (years)
10
Figure 53-9. Mean annual body weights of two spotted
seals from ages 1-9 years.
subadult animals, then in the adults (Scheffer and
Slipp 1944, Pitcher and Calkins in press).
A relationship between the molt and plasma thy-
roxine and plasma Cortisol levels has been reported
MOLT
10
c
1
o
1
< - 6
O CO
_I +1
O IX c
CO — »
<
in captive Atlantic harbor seals (Riviere et al. 1977;
Engelhardt 1977, 1979). The onset of shedding is
accompanied by a decrease in plasma thyroxine and
an increase in plasma Cortisol. With completion of
shedding, there is a marked increase in thyroxine and
decrease in Cortisol to pre-molt levels. The change in
plasma thyroxine levels suggests, in view of the
known effects of thyroid hormones on basal metabo-
lism (Hoch 1971, 1974), that correspondingly large
changes in oxygen consumption may also occur in
molting seals.
We measured basal oxygen consumption in three
yearling harbor seals at two-week intervals for two
and a half months, during and after a shedding phase
lasting five and a half weeks. Immediately before the
metabolism tests, a blood sample was collected from
each seal, and concentrations of plasma thyroxine
and plasma Cortisol were determined by radioimmu-
noassay techniques (Reference Laboratory, Newbury
Park, California). The results (Fig. 53-10) confirmed
those of Riviere et al. (1977) and Engelhardt (1977,
1979) and indicated further that the BMR declined
to a minimum of 83 percent of pre-molt levels toward
the end of the molt period. This decline was cor-
related with an increase in plasma Cortisol and a de-
crease in plasma thyroxine, which began two weeks
CORTISOL
-|14
H12 f
o
E
3
-10
E
6 (/)
z
o
2 2
o
z
JULY
AUGUST
SEPTEMBER
OCTOBER
Figure 53-10. Observed variations in basal metabolism, plasma thyroxine, and plasma Cortisol for three molting yearling
harbor seals.
886 Marine mammals
before the first observed metabolic change. Metabo-
lism increased gradually to normal levels as Cortisol
decreased and thyroxine increased to pre-molt con-
centrations.
Reproduction
The energy cost of reproduction in mammals is
generally estimated as the summation of energy
requirements for fetal maintenance and growth,
uterine maintenance, maternal work, parturition, and
lactation, but is complicated by the concurrent
needs of adult growth, activity, and maintenance
(Brody 1945).
Metabolism in pregnant pinnipeds has not been
measured, although Lavigne et al. (1977) estimated
the energy cost of gestation for the harp seal from the
known fetal growth and gestation time. These data
were incorporated into an exponential equation
similar to one developed by Moen (1973) for several
ungulates. Using their estimate of 19.22 kcal/kg
fetal weight at term per day, we assume that the cost
of gestation in the harbor seal is approximately 5.7 X
lO'* kcal for an 11. 7 -kg fetus over 252 days, and in
the spotted seal 3.4 X 10"* kcal per 7.1-kg fetus over
252 days.
The energy cost of lactation in pinnipeds has not
been measured either. Lavigne et al. (1977) esti-
mated the total milk production of a female harp
seal necessary to satisfy the energy requirements of a
pup from another equation supplied by Moen (1973).
Total milk production (MPx ) was related to (1) the
activity increment of a pup in kcal/day (A), (2) the
daily growth increment of the pup (GI) converted to
kcal using the caloric equivalent for whole ringed
seal pups of 5,150 kcal/kg (Stirling and McEwan
1975), and (3) the average daily metabolic rate of a
pup during the nursing period (M, or 2[70W°j^ ])
integrated over the number of days of lactation (n):
MP,
2
i=0
A + GH-M
(4)
The total energy cost of milk production to the
female harp seal was based on information on dairy
cattle and assumed to be 1.6 MF^ (Crampton and
Harris 1969). For harbor seal pups with an activity
increment (A) of about 444 kcal/day (ADMR-BMR),
a growth increment (GI) of 0.46 kg/day (or 6.6 X
lO'' kcal over the lactation period), and a lactation
period of 28 days, the total energy required would be
1.6 MPt = 1.8 X 10^ kcal. The figure calculated
for spotted seals with A = 0 (see Table 53-10), GI =
0.61 kg/day (8.9 X 10^ kcal total), and n - 28 days
is 1.9 X 10' kcal.
EXTRAPOLATION TO THE
NATURAL POPULATION
Two models were employed to estimate the annual
cost of free existence for wild populations of harbor
and spotted seals in the Bering Sea: Model I was
based on the food consumption of captive seals used
in this study (Fig. 53-3), and Model II was based on
estimates of daily metabolism for individual age-
classes derived from metabolic data on resting and
active seals (Fig. 53-5). Table 53-9 summarizes the
basic assumptions and prediction equations for each
model.
Mean body weights of harbor seals 0-24 years old
were determined from data on seals collected from
Aleutian Ridge and Pribilof Islands populations by
Bums and Goltsev (in preparation), as previously
described. Mean body weights of spotted seals 0-3
years old were calculated from a regression of data
from seals used in this study. Mean weights of
spotted seals 4-24 years old were estimated from a
regression of weight/age information on captive
animals and maximum body weights of wild speci-
mens (Tikhomirov 1971, Popov 1976). The mean
body weight of the 0 age-class of each species was
estimated as the average weight of animals from
weaning to 1 year of age. Age-frequencies in a popu-
lation of 1,000 seals were estimated from mortality
and reproductive rates for each species. Mortality
and reproductive rates for harbor seals were based on
those estimated for the Gulf of Alaska population by
Pitcher and Calkins (in press) and the British Colum-
bia population by Bigg (1969), and mortality rates
for spotted seals were taken from Popov (1976).
Since there are no data on the reproductive maturity
of spotted seals, reproductive rates for these seals
were assumed to be the same as those of harbor seals.
These assumptions were made about the steady-
state characteristics of each population: (1) the
age-specific reproductive, mortality, and growth rates
remain constant over the range of age-classes; (2) the
sex ratios in each age-class are even; (3) sexual di-
morphism is minimal (i.e., body weights have been
averaged over both sexes); (4) the mortality in each
class is natural (the population is unexploited); and
(5) the population is healthy (parasite loads and
disease are minimal).
With Model I, the annual net caloric intake of
pollock or herring was calculated for each age-class
from the computed mean body weight, age-
frequency, computed food intake (as percentage of
body weight), and gross and net energy contents of
each prey item. Since the equation used to predict
food consumption was derived from data collected
Energy cost for harbor and spoiled seals 887
I
from seals which did not reproduce during captivity,
an estimate of the caloric cost of reproductive effort
was added to the food intake of all pregnant females
as calculated from age-specific pregnancy rates and
age-frequencies. This estimate is a little too high,
since not all the pregnant females will carry a fetus to
term, and experience lactation costs. The food
consumption of the 0 age-class was estimated as that
of weaned-to-yearling pups (over a 337-day period, or
365 days minus lactation time), because the intake of
nursing pups was accounted for by the lactation costs
included in reproductive effort.
Before assessing energy requirements by Model II
methods, we need to know the diurnal activity pat-
terns of each species in order to estimate the exis-
tence metabolism (EM), or average daily metabolic
rate (ADMR), which is equal to the total net energy
expended per day (see Equation 2 of text). Sullivan
(1979) has provided a quantitative budget of daily
activity for a colony of Pacific harbor seals which he
observed in northern California. We have applied this
activity regime to Bering Sea harbor and spotted
seals, with some modifications to take into account
known variations in behavior associated with molt,
reproduction, and habitat for each species.
Table 53-10 presents activity budgets for several
age-classes of seals with estimates of net expenditure
of energy for each activity (in multiples of basal
metabolism) based on metabolic measurements.
This table was used to calculate the daily net energy
requirements of populations of harbor and spotted
seals. It was assumed that spotted seals spend more
time in water than harbor seals (60.3 percent vs.
56 percent) during the nonreproductive and nonmolt-
ing seasons, on the basis of observations that they are
more migratory and less gregairious than harbor seals
(Burns 1970, Burns et al. 1972, Fay 1974,
Shaughnessy and Fay 1977). During the pupping and
mating seasons, adult spotted seals form widely
separated pairs at the ice front for about two months
Body weight
W = weight
Harbor Seals
t = 0
l<t<5
5 < t < 24
Spotted Seals
t = 0
l<t<4
4 < t < 24
TABLE 53-9
Basic assumptions and prediction equations for Energy Flow Models I and II.
MODEL I & MODEL II
) t = age (yrs)
W = 24.5 (mean value from weaning to 1 yr)
W = 33.3 e'^-i^* (r=0.97)
W = 118.5-127.6 e^-^^* (r = -0.98)
W = 24.9 (mean value from weaning to 1 yr)
W = 17.3 e°-3^ (r = 0.95)
W = 102-95.6 e-°-2^* (estimated)
Gross energy of food (GE), net energy of food (NE)
Herring: GE = 2143 kcal/kg (= 12% fat), NE = .80 GE
3. Reproductive effort = gestation + lactation costs
= 19.22 Real (kg fetus/day) + 1.6 MPt (see Equation 4 in text)
MODEL I
Food intake
0 < t < 24
I = intake (% W) t = age (yrs)
I=12.2(t + l)-°-^'^ (r = -0.94)
MODEL II
4. Existence metabolism (EM) = basal metabolism +
activity + growth + reproduction + molt = n BMR
t = Birth to Weaning BMR = 85.5 kcal/(kg day)
t = Weaning to 1 yr BMR = 59.5 kcal/(kg day)
l<t<4 BMR = 57.5 kcal/(kg day)
4<t<16 BMR = 57.4 - 2.25t (estimated)
t < 16 BMR = 70 W°-^^ kcal/day
888 Marine mammals
TABLE 53-10
Estimated daily activity patterns and net cost of activity for Bering Sea harbor and spotted seals in
relation to molt, reproductive, and other seasons. B = birth, W = weaning.
Percent
Harbor seals
of day and
net energy cost (
:n BMR)
Spotted seals
B-lyr
1-24 yrs
B-W
W-24 yrs
Activity
Molt
Other
Molt
Repro.
Other
Water
Swimming
Sleeping
60.3(1.6)
90.7 (0.8:B-W)
(0.7:W-1)
30(1.35)
56(1.5)
Assume
activity =
30(1.35)
56 (1.5)
60.3(1.5)
9.7(0.7)
Land
Alert behavior
Movement
Comfort behavior
Agonistic behavior
Sleeping
3.7(1.3)
3.6(1.7)
1.3(1.2)
0.6(2.1)
20.8
(0.8:B-W)
(0.7:W-1)
8.6(1.17)
8.4 (1.53)
3.2(1.08)
1.3(1.89)
48.5(0.7)
5.4 (1.3)
5.3(1.7)
2.0(1.2)
0.8(2.1)
30.5(0.7)
land activ-
ity and
NE cost
= BMR
8.6(1.17)
8.4 (1.53)
3.2(1.08)
1.3(1.89)
48.5(0.7)
5.4(1.3)
5.3(1.7)
2.0(1.2)
0.8(2.1)
30.5(0.7)
3.7(1.3)
3.6(1.7)
1.3(1.2)
0.6(2.1)
20.8(0.7)
Growth increment
GI (kg/day)
0.46 (B-W)
0.04 (W-1)
0.017 (lyr)
0.020 (2 yrs)
0.023 (3 yrs)
0.016 (4 yrs)
GI = 0.057 e
1
-o.ist
0.61
0.004 (W-1 yr)
0.033 (lyr)
0.049 (2 yrs)
0.041 (3 yrs)
GI = 0.063 e-°-'«*
(5yrs<t<24yrs)
(4 yrs < t < 24 yrs)
Reproductive
0
855.5 (4-24 yrs)
0
796.4(4-24:
yrs)
effort (kcal/day)
over 280 days
(Bums et aL 1972, Fay 1974). It was assumed that
non-aquatic activity in this species at that time was
equal to that exhibited by harbor seals during their
reproductive season (44 percent). From the observa-
tions of SulUvan (1979) and others (Bishop 1967;
Wilson 1974a, 1974b), it was assumed that harbor
seal pups are active after birth, spending more time
in water than subadults and adults (70 percent vs.
56 percent). Spotted seal pups are reported to be
quite sedentary after birth, becoming aquatic only
after the lanugo is shed at weaning (Burns 1970,
Naito and Nishiwaki 1972). Thus, they were
assumed to require energy primarily for basal metabo-
lism until weaning, after which their activity levels
and energy requirements were considered equivalent
to those of harbor seal pups. It was assumed from
observations of harbor seals during this period that
members of both species remain out of water for
long periods during the molt (Johnson and Johnson
1979). The proportion of time allotted for each
behavior exhibited by seals on land was kept constant
in each activity budget estimated for reproductive,
molting, and other periods.
The annual net energy requirements of each
population of 1,000 seals, as predicted by both
models, is shown in Tables 53-11 and 53-12. The
close agreement between net energy requirements
for age-classes 2-24 predicted by Models I and II
reflects a high correlation between food intake and
metabolic data for captive seals (r = 0.97). The large
differences between the two models for age-classes
0 and 1 may be caused by greater activity and con-
sumption of food by young captive seals than by
animals in the wild, as a result of adjustment to
captivity.
Using the means of the predicted net energy values
as best estimates of the annual net energy require-
ments of each class, it is apparent that about 40 per-
cent of the total annual net energy required by each
population is necessary to sustain the 0-3 age-classes
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890
Energy cost for harbor and spotted seals 891
in harbor and spotted seals. This is a result of the
higher growth rates, the higher age-frequency of this
class in the population, and higher basal metabolism
of young seals as compared to older animals. In both
species, the component of net energy necessary for
growth comprises more than 50 percent of the total
annual requirement in newborn to weanling seals, 7-2
percent in weanling to 3-year-old seals, and less than
2 percent in seals 4 to 24 yeairs old. According to our
estimates, individual pregnant and lactating seals of
both species require 13 percent or more net energy
per year than males and nonreproducing females, the
fraction of the total annual cost required by repro-
ductive effort possibly increasing with age because of
decreasing basal metabolism.
Table 53-13 presents estimates of the percentage of
annual gross energy requirement and proximate
composition of four prey important in the diets of
Bering Sea heirbor and spotted seals. Available data
on seasonal food habits suggest that these species
may provide a major portion of the annual gross
energy requirement of both seal populations; their
rank in importance in the diet of seals is shown in the
table. We have assumed negligible intake of other
prey and negligible variation in food habits with age
in order to simplify the computations, although
present evidence suggests that other prey are taken
and younger animals may consume more inverte-
brates and smaller finfish than older seals (Pitcher and
Calkins in press; Frost, personal communication).
Variation of fat content in capelin (Mallotus villosus)
and herring is attributed to the loss of fat in periods
of fasting during spawning migrations in late spring
and early summer, and subsequent replenishment
during vigorous feeding after spawning (Stoddard
1968, MacCallum et al. 1969, Jangaard 1974). Mean
energy values indicative of this trend have been used
to estimate seasonal consumption of capelin and
herring by the seals.
The seasonal and annual consumption of each
prey in metric tons by both seal populations are
presented in Table 53-14. The annual net energy
requirements computed from Models I and II for
1,000 seals in Tables 53-11 and 53-12 were averaged
for each seal species, divided equally between two
general seasons (spring and summer, fall and winter),
and extrapolated to the seasonal populations of
Bering Sea harbor and spotted seals as estimated by
McAlister et al. (1976). The total net energy require-
ment per season (NE^ ) for each seal population was
TABLE 53-13
Percent of total gross energy required and proximate composition of four important prey in the diets of
Bering Sea harbor and spotted seals. S = spring and summer; W = winter and fall.
% Gross energy
requirement
S W
Proximate composition
Species
%H2 0
% Protein
% Fat % Ash
Energy
(kcal/kg wet)
Reference
Pollock
Theragra
chalcogramma
10.0
20.0
78.8
19.2
0.8 1.6
1088
This study
Capelin
Mallotus
villosus
20.0
10.0
77.1-82.3
12.9-15.0
12.3-15.0
8.1-1.8
23.4-6.5 -
x=1254*
x= 2177*
MacCallum et al.
1969 (spawning
capelin)
Jangaard 1974
(feeding capelin)
Herring
Clupea harengus
pallasi
15.0
10.0
64.0-71.7
16.3-20.0
18.0-5.1 2.0-2.4
2418-1564
This study
Invertebrates
(cephalopods,
crustaceans)
5.0
10.0
79.9-80.2
12.5-17.8
1.4-0.9 1.4-2.2
X = 964*
Geraci 1975
*Calculated from proximate composition data.
892 Marine mammals
TABLE 53-14
Seasonal gross energy requirements and intake of four important prey by Bering Sea harbor and spotted seals.
S = spring and summer; W = fall and winter.
Population
(X 10^)
S W
Gross energy
(kcalX 10'°)
S W
Prey intake
(mtX 10^)
Species
Pollock
S W
Capelin
S W
Herring
S W
Invertebrates
S W
Harbor seal
Spotted seal
1.5 1.5
1.25 2.5
12.6 12.6
10.2 20.4
11.6
9.4
23.1
37.5
20.2
16.3
5.8
9.4
12.1
9.8
5.9
9.5
6.5 13.1
5.3 21.2
Total /season
Total/year
21.0
60.6
81.6
36.5
15.2
51.7
21.9
15.4
37.3
11.8 34.3
46.1
converted to total gross energy (GE^ ) with the
following equation :
NEt
0.80
GEn
(5)
where 0.80 is the net energy coefficient determined
in feeding and metabolic tests with pollock and
herring. The fraction of the gross energy represented
by each prey (GE;) was then converted to metric
tons consumed (I) with use of the appropriate seas-
onal caloric content (E), as in the following example:
Capelin in Harbor Seal Diet
Spring and Summer:
GEi 25.2 X 10' kcal
E 1.25 X 10^ kcal/kg
= 20.2 X 10^ mt
Fall and Winter:
GEj 12.6 X 10' kcal
E 2.18 X 10^ kcal/kg
= 5.8 X 10^ mt
(6)
Comparison of annual consumption data for
pollock and herring from Table 53-14 with recent
commercial fishery statistics (Pereyra et al. 1976,
NMFS 1977) suggests that the pollock and herring
consumption of both seal populations may be about
8.6 and 19.6 percent, respectively, of the commercial
take of these fishes.
The ecological efficiency of each seal species was
calculated according to the definition of Slobodkin
(1960) for a steady-state population, where yield is
equal to production for any given time period:
Ecological Efficiency = Yield/Ingestion X 100% (7)
Yield was computed at the annual biomass of dead
seals for each population converted to kilocalories
using the caloric equivalent for seal tissue (4,240
kcal/kg) derived by Stirling and McEwan (1975)
for 25 ringed seals. Ingestion was equivalent to the
annual gross energy required by each population in
kilocalories. Ecological efficiency was 2.27 and 2.23
percent in Bering Sea harbor seals and spotted seals,
respectively. These efficiency values are nearly
identical and consistent with those obtained for harp
seal (Lavigne et al. 1977) and ringed seal (Parsons
1977) populations using similar energy budget
models, and are in agreement with predicted results
for homoiotherms (Turner 1970, Steele 1974).
ACKNOWLEDGMENTS
We thank Mike Ashwell, Sally Dunker, Howard
Ferren, and Dan Wilm for valuable assistance. Dr. Dan
Holleman for guidance with isotope counting tech-
niques. Dr. Francis Fay and Kathy Frost for critical
review of the manuscript, and Dr. Robert Dieterich
for veterinary medical advice. This study. Contribu-
tion No. 425, Institute of Marine Science, Univer-
sity of Alaska, Fairbanks, was supported in part by
NIH Research Grants HL-16020 and HL-23950,
the Sea Grant Program, the Alaska Heart Association,
and Seward Fisheries, Seward, Alaska.
Energy cost for harbor and spotted seals 893
I
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Seetion E
Microbiology
Richard Y. Morita, editor
Microbiology of the Eastern Bering Sea
Richard Y. Morita
Department of Microbiology
and School of Oceanography
Oregon State University
Corvallis, Oregon
I
I
I
I
I
INTRODUCTION
Scientists attempting to understand the marine
environment are beginning to take microbiology into
account; many of the mysterious "black boxes"
in oceanography can be explained in the light of
microbiological processes.
All higher forms evolved in the vi^orld of pro-
caryotic cells. This is cleairly seen in biological
oceanographic processes, where bacteria enter into
many types of relationships with the higher forms:
they cause diseases, serve as food, live as epiphytes,
endosymbionts or parasites, or simply inhabit their
intestinal tracts.
Chemical oceanographers now know that many
of the various gases found in seawater and sediments
are both used and produced in microbial metabo-
lism—especially dinitrogen oxide, hydrogen, and
methane. Microbes also make and use phosphate,
nitrogenous compounds, and inorganic sulfur com-
pounds.
Geochemically, the marine bacteria have been
found to be involved in the diagenesis of sedimentary
material, in the formation of calcite, gases in bottom
deposits, authigenic carbonates, and sulfide minerals,
and in changes in the pH and Eh of sedimentary
material.
CURRENT STATUS OF THE MICROBIOLOGY
OF THE EASTERN BERING SEA
Unfortunately, the microbiology of the eastern
Bering Sea has been investigated very little. The
microbiological studies that have been done are too
recent to report; the data gained by the microbiolog-
ical team at the University of Louisville under Dr.
Atlas and our group (R. P. Griffiths, W. Broich,
B. Caldwell, R. Y. Morita) have not been completely
analyzed. The few studies that have been done deal
with the microbiology of fish (mainly pathogens)
(McCain and Gronlund, Chapter 55, this volume) and
the pathology of the mammals and birds in this area.
Salmonella in fur seals
Salmonellosis, commonly known as bacillary
dysentery, was reported in the northern fur seal
(Callorhinus ursinus) on St. Paul Island in 1951 by
Jellison and Milner (1958). The organism Sa/mone//a
enteriditis was isolated from the blood and tissue of
5 of 12 neonatal seal pups examined and from
seal lice (Antarctophthirius callorhini and Proechi-
nophthirius fluctus) (R. K. Stroud and M. E. Roelke,
Oregon State Univ. and Washington State Univ., per-
sonal communication). Stroud and Roelke also
examined a male fur seal pup found dead on Staraya
Artil rookery, St. George Island, 25 July 1977 and
found S. enteriditis to be present. Since the rookery
is crowded, contaminated with fecal material, and
littered with decomposing carcasses of seal pups and
adults, infection with S. enteriditis can easily occur.
Several potential sources of S. enteriditis are also
present on the Pribilof Islands, which are inhabited
by wild animals and birds that serve as reservoir hosts
for salmonella. Salmonella occurring in populations
of wildlife may spread to domestic animals and
people.
Leptospirosis in fur seals
Leptospira, which causes abortion and neonatal
death among cattle and swine, has been isolated from
fur seals on St. Paul Island (Smith et al. 1974) and
in the Bering Sea (Smith et al. 1977). From the
903
904 Microbiology
studies of Smith et al. (1977), it appears that the
infection is acquired after the fur seal pups leave the
rookeries, presumably through the food chain during
their pelagic cycle. Studies by Smith et al. (1978)
strongly suggest that marine mammals carry disease
agents which may pose a threat to swine and other
domestic, laboratory, or captive species and that
some of these agents may also be communicable
to human beings.
Bacteria associated with birds
No salmonella or pasteurella could be detected
in the cloaca specimens obtained from birds col-
lected on St. Paul Island. However, Escherichia,
Enterobacter, Hafnia, Moraxella, and Acinetobacter
were identified (B. C. Esterday, Univ. of Wisconsin,
personal communication).
Viruses in birds
No influenza virus could be detected from swab
samples taken from the tracheae and cloacae of
birds collected on St. Paul Island (B. C. Esterday,
Univ. of Wisconsin, personal communication). How-
ever, Newcastle disease viruses were recovered from
three murres and a cormorant on St. Paul Island and
from an arctic tern at Barrow. Results of testing for
various viruses on birds collected on St. Paul Island
and at Barrow have been inconsistent. No influenza
viruses were recovered in the summers of 1975 and
1977, but 68 influenza viruses were recovered in
1976 on the island. Five influenza viruses were
recovered at Barrow in 1975 and two in 1976.
Three viruses were isolated from seabird para-
sites (Ixodes uriae) collected from St. Paul Island,
and an obivirus was found in the blood of a seabird
on St. Paul Island (B. C. Esterday, Univ. of Wisconsin,
personal communication). No indications could be
found that these viruses are responsible for any
disease among birds.
Preliminary microbiological data from the eastern
Bering Sea
Vibrio spp. were isolated from sediments taken
from Dutch Harbor, Alaska, by H. M. Feder, S. A.
Norrell, and K. Babson (Univ. of Alaska, personal
communication). No Vibrio parahaemolyticus (a
marine bacterium that is a human pathogen) were
isolated from this area, probably because of the
cold temperature of the sedimentary material asso-
ciated with seafood-processing wastes at Dutch
Harbor. However, V. alginolyticus and V. anguil-
larum (the cause of vibriosis in salmonid fish) were
found in the sedimentary material, along with chi-
tinoclastic bacteria.
The preliminary data gathered by Atlas (Univ. of
Louisville, personal communication) in microbiolog-
ical studies in the eastern Bering Sea are as follows:
(1) The counts of viable bacteria in surface water
are similar to those for the Gulf of Alaska. Even in
the Bering Strait these counts are one to two orders
of magnitude below viable counts in the Beaufort
Sea. (2) The numbers of hydrocarbon utilizers were
no higher in the Norton Sound near the seep areas
than in the Lower Cook Inlet and may have been
depressed. There was a great deal of variability in
counts of hydrocarbon utilizers within Norton
Sound. (3) There is a difference between northern
and southern Bering Sea sites with respect to deni-
trification potentials. Natural rates (ng N2O pro-
duced per g sediment per 10-day incubation) were
often 0 in northern Bering Sea sites but 10^ in all
southern Bering sites. When NO3 was added, how-
ever, rates were generally 10"* in northern sites and
10^ in southern sites. This may be interpreted as
meaning that denitrification potentials are higher in
the northern than in the southern Bering Sea, and
that under natural conditions in the north, NOJ is
not available for denitrification, whereas in the south,
there is a natural pool of NO^ available for denitrifi-
cation.
Measurements of microbial activity in the water
masses associated with the Norton Sound area indi-
cate that the level is relatively low (measured by the
heterotrophic potential method) within a radius of
120 km from the eastern tip of St. Lawrence Island
(Griffiths, MacNamara, Caldwell, and Morita, unpub-
lished data). These waters showed high salinity as
well as high respiration (mineralization). The waters
at another location within Norton Sound were of
lower salinity because of the influx of fresh water
from the Yukon River, and the microbial activity
showed a pattern the reverse of that in the water mass
near St. Lawrence Island. A statistical analysis of the
relationship between salinity and microbial activity
indicates that there is an inverse relationship signifi-
cant at the p< 0.0005 level. The highest levels of
microbial activity were observed in fresh water from
the Yukon River. However, it should be emphasized
that this area has been sampled only once (July
1979).
Further analysis within this area shows high
microbial activity near Nome, near the seep area.
In the seep area, crude oil reduced the uptake of
glucose of the microbial population less than in the
other areas studied. Again a statistical difference is
noted. The crude oil dispersant Corexit also affects
microbial activity in these areas.
Microbiology 905
\
MICROBIAL INTERACTIONS WITH THE
BIOLOGY OF THE SEA
Procaryotic cells evolved before eucaryotic organ-
isms. During the Precambriein period the procary-
otic cells developed many biochemical pathways to
cope v^rith the environmental changes that occurred.
The eucaryotic cells then evolved in a world of
procaryotic cells; as a result many relationships, some
of which we still do not fully understand, developed
between higher organisms and microbes. Protozoans
needed food (energy) to carry out their metabolism.
Bacteria were available for consumption; therefore
bacteria, as well as the photosynthetic organisms, can
be thought of as a primary trophic level.
From an evolutionary point of view it makes good
sense that the large biomass of bacteria should serve
as the source of food for many organisms, especially
in view of the low C/N ratio in bacteria. Further-
more, the development of bacteriovores may be just
as important in the development of the higher evolu-
tionary forms as that of the higher trophic levels.
Standing crop
ZoBell (1961) estimated the standing crop of
bacteria in the oceans to be of the order of 10^ mt
of organic carbon. In 1963 Kriss estimated that
there were from 2.9 X 10^ to 2.3 X 10^ bacteria
per ml of seawater. Most of the earlier values were
based on the viable (plate) count method. The direct
count of bacteria in seawater is from 13 to 9,700
times greater than the viable count (Jannasch and
Jones 1959). The direct count does not take into
consideration whether or not the cells are viable,
dormant, or dead, but the status of life makes little
difference to the organisms consuming the bacteria.
However, new techniques have been developed for
measuring the number of bacteria in seawater:
the adenosine triphosphate (ATP) method (Holm-
Hansen and Booth 1966), the epifluorescent tech-
nique (Daley and Hobble 1975, Hobble et al. 1977,
Francisco et al. 1973, Zimmermann and Meyer-
Reil 1974, Watson et al. 1977), muramic acid deter-
mination (Moriarty 1975, King and White 1977),
lipopoly saccharide (LPS) (Levin and Bang 1964,
Watson et al. 1977), and transmission electron
microscopy (Watson et al. 1977). Some of the
current data indicate that the numbers of bacteria
are greater than those reported by Kriss (1963).
There are some indications that the bacterial
biomass is equal to the standing crop of all other
organisms in the sea, if not greater. Yamaguchi and
Seki (1977) estimated the microbial biomass in
Shimoda Bay, Japan, to range from 11.5 to 100
percent of the particulate organic carbon. Total
bacterial biomass ranges from 1.3 percent to 100
percent of the particulate organic carbon. Watson et
al. (1977) found between 1.5 X 10^ and 6.29 X lO**
cells by the epifluorescent count in 188 samples from
waters near Woods Hole, cruise No. 8 of the R/V
Oceanus (Sargasso Sea), and cruise No. 93, leg 3 of
the R/V Atlantis II (southwest African coast). They
also found a high correlation between LPS concentra-
tions and bacterial numbers in the 188 samples.
According to Gallardo (1977), over 50 percent of
the standing crop biomass under the Peru-Chile sub-
surface countercurrent is made up of filamentous
bacteria of the genus Thioploca. His data strongly
suggest a possible trophic relationship between the
bacteria and the principal shrimp and hake in this
area. When more data have been accumulated with
the modern techniques for estimating the number of
bacteria in sea water, a more reliable standing crop
figure can be obtained.
Bacterial productivity
Although estimates of the standing crop may be
of interest to the biological oceanographers, the
productivity of the bacteria mass is actually more
important because it contributes constantly to the
various trophic levels. Bacterial counts in seawater
and sediments are probably never high enough to
do justice to real numbers, because bacteria are
continually being cropped by protozoa, copepods,
sponges, bivalves, and shrimps, in addition to bac-
teriophages (Torrella and Morita 1979). Waksman
and Carey (1935) believed that the protozoa and
copepods are primarily responsible for depleting the
bacteria in seawater (see section on bacteria as food).
Bacterial production in the ocean is well discussed
by Sorokin (1974), who states that, in coastal zones,
bacterial production is of the same order of magni-
tude as phytoplankton production. He obtained
values for bacterial production in the range of 0.3-1
gm/m^ /d in the Black and Japan seas. Tilzer (1972)
states that bacterial productivity is of the same order
of magnitude as the autotrophic productivity in a
high mountain lake.
Generation time (for one cell to divide into two)
has been estimated by Kutznetsov et al. (1962) at
about two weeks. This estimate takes into considera-
tion the nutrient-poor waters of the deep open ocean.
However, if all conditions are optimal for the growth
of bacteria, the generation time can be very short.
Eagon (1962) was able to demonstrate a generation
time of 9.8 minutes for Pseudomonas natriegens
(a marine bacterium). Escherichia coli is considered
to have a generation time in the laboratory of about
906 Microbiology
20 minutes. If there were a sufficient supply of
energy in any given environment and other conditions
were optimal, the productivity per year would be
extremely great.
To determine the number of bacteria that might
be able to grow in any given environment, the num-
ber released by biodeposition must be considered.
For instance, from 6.7 X 10^ to 1.3 X 10^ bacteria
per gram of intestinal content were found in a feeding
sea bream (Sera et al. 1974). These figures were
obtained by the pour plate method; a direct count
would probably yield much higher figures. The
bacterial count in human feces can be on the order
of 3.2 X 10" cells/g (wet weight) (van Houte and
Gibbons 1966). The bacterial mass then would be
equal to 30 percent of the total wet weight of the
feces (Moore and Holdman 1974). Thirty percent
of the amount of biodeposition at all trophic levels
produced in the course of development of large fish
would amount to a considerable biomass.
Productivity of bacteria and cropping are dis-
cussed in the work of Barsdate et al. (1974), Harrison
and Mann (1975a and b), and Fenchel and Harrison
(1976). Fenchel and Harrison (1976) demonstrated
in the laboratory that a cell population of over 10^°
bacteria per ml can be maintained when there are no
flagellates or ciliates present in a system with eel-
grass as the substrate. However, when flagellates
were added to the system, the population of bacteria
dropped more than an order of magnitude. When
both flagellates and ciliates were added, the drop in
the number of bacteria was more than two orders of
magnitude.
Bacterial nutrient regeneration
The biochemical cycles brought about by bac-
terial transformation of organic matter and inorganic
nutrients are discussed by various investigators such
as ZoBell (1946), Harvey (1955), and Russell-Hunter
(1970). These are the nitrogen cycle, the phosphorus
cycle, the carbon cycle, and the sulfur cycle. Bac-
teria have been assigned the role of decomposers in
the trophic -level scheme.
In the carbon cycle, the amount of cairbon dioxide
fixed by the marine photosynthetic organisms is
approximately 1.6 X 10'^ kg/yr (Steemann-Nielson
1952). Such an amount of material must be decom-
posed by one means or another that an equal amount
of carbon dioxide can be regenerated. During the
decomposition of this material, mostly by bacterial
action, new bacterial cells are also produced. During
the decomposition of organic carbon compounds
containing phosphate, sulfur, or nitrogen, primary
nutrients such as phosphate, nitrate, nitrite, ammonia,
carbon dioxide, sulfate, and phosphate are produced
so that the cycle can begin again. The formation of
some of the compounds listed also occurs in sedi-
mentary material and will be discussed under the
chemistry and geology of the oceans. To illustrate
the magnitude of the bacterial decomposing process,
Russell-Hunter (1970) stated that
if all decomposing bacteria ceased their activities for
only three months, then nearly all green plant produc-
tion on this planet would cease almost immediately,
and no higher animals (including man) could survive
the temporary interruption of bacterial recycling.
At the present time we have no foolproof method
of measuring the rate of microbial decomposition. The
most acceptable technique we have is the hetero-
trophic activity method (Parsons and Strickland
1962, Wright and Hobbie 1965), which measures the
microbial activity (uptake) of specific radioactive
compounds. The amount of respired ''*C02 from
'''C-labelled compounds (uniformly carbon labelled)
used in the heterotrophic activity method is actually
the amount of mineralization of the compound
resulting in CO2 formation (Harrison et al. 1971).
Naturally there are loopholes in the process due to
the addition of a specific labeled compound into
the system; nevertheless, it is the best current method
of measuring microbial rates in natural aquatic
systems.
Bacteria as food
The nutritive value of bacterial cells is much
higher than that of phytoplankton cells since bacteria
are richer in proteins (hence rich in essential amino
acids), phosphates (the nucleic acids and polyphos-
phates), carbohydrates, fatty acids, and growth
factors (vitamins or ectocrine compounds). Bacteria
adhere to particulate matter as well as detritus and
therefore are ingested along with these materials.
Hence detritivores are also bacteriovores. The meas-
urement of particulate organic carbon and dissolved
organic carbon in oceanography usually does not
indicate the nutritive value of the material, but this
must be taken into consideration in studies of the
efficiency of biological productivity.
Production of bacterial cells can come from
growth on fecal material and from the use of organic
matter (both dissolved and particulate), including the
dissolved organic matter that results from terrestial
runoff. Cells produced in this way, used as food, add
to the productivity of the oceans.
Much of the early work on bacteria as food is
cited by ZoBell (1946). A list of various organisms
known to utilize bacteria as food is provided by
Microbiology 907
Sorokin (1974). Unicellular algae (including the
cyano bacteria) can be used as food also, but this
subject will not be discussed here since it is so well
presented by Ryther and Goldman (1975).
Where land drainage takes place, terrestrial bacteria
are introduced into the marine environment. Bays
and estuaries add more bacteria to the offshore
environment. For instance, ZoBell and Feltham
(1942) determined bacterial counts for inflowing and
outflowing water at the mouth of Mission Bay
(California) for a period of 34 days and found an
average of 9,600/bacteria/ml in inflowing water and
294,800 bacteria/ml in outflowing water. Sewage
material also contains large numbers of bacterial cells;
as many as 17,200,000 fecal coliforms/100 ml of
residential sewage have been counted (Geldreich
1966). This figure is for coliform only, but marine
ciliates can feed on Escherichia coli (Mitchell 1972),
and the redbeard sponge has been shown to remove
microbial pollutants from waste effluents (Glaus et al.
1967).
No attempt will be made to draw a line of de-
marcation between organisms that ingest single
bacteria and those that eat aggregates of bacteria,
bacteria on detritus, and bacteria associated with
fecal pellets. However, any organism that is
considered a filter feeder, suspension feeder, or
detritus feeder is a bacteriovore, because bacteria
are associated with such particles. The attachment
of bacteria to various particles in seawater has been
studied. Whether most bacteria in the sea are
free living or attached to various particles has yet
to be determined. Bacteria also have the ability
to aggregate, and aggregation of bacterial cells
may also result from bubble formation (Barber
1966, Riley 1963).
That bacteria are important in arctic trophic
levels is well illustrated by the research of Siebert
et al. (1977), who demonstrated that bacteria are
eaten by the herpacticoid copepod, which, in turn,
is the main food of juvenile salmon. Invertebrates
such as oysters, barnacles, tunicates, and copepods
can ingest large quantities of small particles ranging
from 1 to 5 M (Dumas 1935, Verway 1952,
Jorgensen 1966, Haven and Morales-Alamo 1970).
Bacteria can be ingested for growth and maturation
by spongillids and sponges (Reiswig 1971 and
1975) and by Mytilus californianus (ZoBell and
Feltham 1938). Coral of all types can eat and
digest bacteria (DiSalvo and Gunderson 1971,
Sorokin 1973). Bacteria growing on the organic
matter of the seawater passing over coral reefs are
the main source of energy of the biological popula-
tion of the reefs (Sorokin 1973). The percentages
of bacterial cells assimilated to consumed food
(expressed as carbon) for some coral reef organisms
are: gastropods (veligers), 61 percent; hydroid
(Pennaria tiarella), 74 percent; annelid (Serpulidae),
73 percent; coral (Pocillipora damicornis),16 percent;
coral (Montipora verrucosa), 82 percent; sponge
(Toxadocia uiolacea), 82 percent; tunicate (Ascidia
nigra), 83 percent; holothurian (Ophiodesoma spec-
tabilis), 22 percent; gastropod (Nerita picea), 20 per-
cent; and lamellibranch (Grossotrea gigas), 68 percent
(Sorokin 1973). However, these data need to be
verified by other investigators.
Detritus is frequently defined as dead organic
matter, but Darnell's definition (1967) takes into
consideration the microbial content of detritus.
He defines detritus as "all types of biogenic mate-
rial in various stages of decomposition that repre-
sents a potential energy source for consumer species."
The importance of the detritus-bacteria relationship is
emphasized by various authors in Melchiorri-Santolini
and Hopton's (1972) book. It has been found that
detritus alone cannot satisfy the nutritional require-
ments of detritivores (Seki et al. 1968), but inocu-
lated with Pseudomonas sp. the detritus can be used
as a food source by Artemia (Seki et al. 1968). It is
believed that, when detritus is ingested, the surface
microbial population is stripped off in the gut of the
consumer and the unused portion of the detritus is
egested. The egested particle is again colonized by
bacteria, and the cycle is repeated (Darnell 1967,
Odum and de la Cruz 1963).
According to ZoBell and Feltham (1938), bacteria
are efficient in converting and utilizing detrital waste.
It has been suggested that 90-95 percent of all pri-
mary production flows through detritivores and that
the microorganisms attached to detrital particles
serve as the primary carbon, nitrogen, and energy
source for detritus-feeding organisms (Adams and
Angelovic 1970, Darnell 1967, Day et al. 1973,
Fenchel 1972, Fenchel and Harrison 1976, Hargrave
1970, Heald 1969, Mann 1972, Moriarty 1976,
Newell 1965, Odum and de la Cruz 1963, Tenore
1975). The carbon /nitrogen ratios of Spartina and
brown algae are 45:1 and 40:1 respectively. When
bacteria colonize the leaves, the carbon /nitrogen ratio
of the Spartina detritus is lowered to 11:1. As a
result, the organisms in the second trophic level show
an excellent carbon/ nitrogen ratio of 6.5:1.
Only 2-15 percent of the detritus surface is colo-
nized (or there are between 2 and 15 bacteria per 100
Mm) (Fenchel 1970, 1972, and 1973). Bacterial
growth appears to be stimulated by the presence of
microbial grazers (Fenchel 1973, Hargrave 1970,
908 Microbiology
Johannes 1965, Newell 1965). Meiofauna mechani-
cally break down the detrital particles (creating more
surface area), so that more area is subjected to
microbial action (Cullen 1973). The smaller the
particle of detritus, the more rapid the microbial
growth (GosseUnk and Kirby 1974).
Phosphate is incorporated into bacterial cells,
mainly as nucleic acids (both RNA and DNA) and
polyphosphate. Johannes (1965, 1968) said that very
little phosphate is released by bacteria. It is well
known that bacteria have the ability to concentrate
phosphate under aerobic conditions and release it
under anaerobic conditions. Using more sophisti-
cated research methods, Barsdate et al. (1974)
demonstrated that the time of total turnover of the
phosphorus pool by bacteria varied from 5 minutes to
more than 10 hours, that bacteria have a high rate of
excretion of dissolved phosphorus both in the inor-
ganic and organic forms, that grazers play a modest
role, and that there is a significant tendency toward
a higher absolute uptake rate of phosphorus per
bacterium at lower concentrations of inorganic
phosphorus.
According to Faust amd Correll (1976), the bac-
terial uptake of phosphate is very fast compared with
algal uptake, and bacterial uptake has been under-
estimated.
The carbon /nitrogen ratio in marine vascular
plants is approximately 15:1, in bacteria approxi-
mately 5.7:1 (Harrison and Mann 1975a, Spector
1956). A carbon /nitrogen ratio of 50:1 sometimes
occurs in marine algae. In order to sustain an animal,
its food must have a carbon /nitrogen ratio of at least
17:1 (Russell-Hunter 1970). The increase in the
percentage of nitrogen in detritus is attributed to the
bacteria colonizing its surface (Newell 1965, Harrison
and Mann 1975b, de la Cruz and Poe 1975). The
colonizing bacteria probably increase the nitrogen
content by being able to remove dissolved nitro-
genous compounds from the seawater or by having
the ability to fix nitrogen. Nitrogen fixation in the
sea by bacteria (including the cyanobacteria) in-
creases the productivity of a given area. When cells
grow, phosphate is also added to detritus particles,
since the growth of bacteria on detritus implies an
increase of nucleic acids. Bacterial colonization of
the leaves of various marsh plants is accompanied by
increases in the concentrations of protein and amino
acids.
Bacteria growing on detrital particles increase
the nitrogen content of the detritus. Fixed organic
nitrogen that occurs in seawater in the dissolved
state and in low concentration can be used by the
bacteria for growth, with the energy source coming
from the detrital particle.
Microbial nitrogen fixation
Nitrogen is one of the important limiting factors
in the growth of organisms in any environment.
Macrophytes can continue to fix carbon dioxide
when there is little available nitrate or ammonia,
resulting in plants with carbon /nitrogen ratios of
the order of 40:1 or 50:1. This low-nitrogen
material can serve as a carbon and energy source,
particularly for those species that can fix free
nitrogen. Many bacterial species, either free-living or
in the intestinal tracts of higher forms, can fix nitro-
gen. The fixation of nitrogen requires a tremendous
amount of energy; the carbon in plants may readily
provide this energy to the bacterial cells.
How much organic nitrogen is formed in the
eastern Bering Sea as a result of microbial nitrogen
fixation? What proportion of the carbon dioxide
is associated with nitrogen-fixing photosynthetic
bacteria? How much fixation is done by bacteria
compared with algal primary production? These
important questions have not yet been answered.
Fixed nitrogen coming in from the drainage of
the various rivers as dissolved organic and inorganic
nitrogen compounds can also be used by bacterial
cells, particularly if the levels of organic nitrogen
compounds are low. Bacteria are more efficient in
assimilating low levels of nutrients than eucaryotic
cells or organisms.
Coprophagy
Most organisms do not use efficiently the food
they ingest; as a result much reduced organic car-
bon ends up as biodeposition. Bacterial cells also
make up part of the excreted material. Biodepo-
sition, as mentioned previously, can result in a
tremendous amount of reduced organic carbon
which may be ingested again or may act as a sub-
strate for the growth of more microorganisms.
Coprophagy does play an important role within
trophic levels, and the bacterial contribution is
also important. For instance, certain shrimp will
not reingest their fecal material until it becomes
"ripe." Growth of the bacterial cells also increases
the ectocrine content of the fecal material.
There are not enough data to assess the role of
coprophagy and the amount of biodeposition in
the transfer of carbon from one trophic level to
another in the Bering Sea.
Bacterial production of vitamins
Although the exact vitamin requirements of
most species in the ocean are not known, the vita-
min requirements of macroorganisms are met by
bacteria and to a limited degree by certain algae
Microbiology 909
(Carlucci 1970). However, some phytoplankton do
require vitamins or a combination of vitamins for
growth (Droop 1962, Provasoli 1963). In neeirshore
environment and productive regions, the concentra-
tion of vitamins does not appear to be limiting
(Ohwada and Taga 1972).
Interaction between bacteria and higher organisms
Muller and Lee (1969) cultured four different
foraminifera in gnotobiotic cultures. When these
foraminifera were grown in bacteria-free cultures,
they failed to reproduce. If bacteria were present,
continuous reproduction could be sustained. The
exact function of microbes in this situation is not
knowTi. Other unknown interactions take place
between Cristispira spp. and various bivalves, and
bacteria and different dinoflagellates (Gold and
Pollingher 1971). Probably other interactions be-
tween bacteria and higher forms are yet to be dis-
covered.
Microbial flora of the intestinal tract
Although investigations of the microflora of
various fish and bivalves have been conducted, we
still do not know what disturbing the normal micro-
flora of these organisms might do to the health of the
animals. However, studies have indicated that the
chitin ingested by fish is enzymatically degraded not
by the chitinase produced by the fish, but by bac-
terial chitinase produced in the gut of the fish
(Goodrich and Morita 1977a, 1977b). We also
recognize that the number of nitrogen-fixing bacteria
in the gut is inversely related to the ability of the
shipworm to obtain combined nitrogen in its diet
(Carpenter and Culliney 1975).
MICROBIAL PROBLEMS ASSOCIATED
WITH THE CHEMISTRY OF SEAWATER
Bacterial activity provides the marine environ-
ment with the catalytic processes involved with
the chemistry of the ocean. Generally the "black
box" concept is invoked in such a situation, and
only the end results of the microbial activity are
measured— phosphate, oxygen level (to some degree),
hydrogen, nitrite, nitrate, nitrogen gas, dinitrogen
oxide, ammonium, carbon dioxide, and sulfur com-
pounds.
Carbon dioxide system
Although the carbon dioxide system in the sea
is discussed in textbooks of chemical oceanography,
little or no mention is made of microbial involve-
ment in the system. If we assume that approxi-
mately 13.6 X 10"* g of carbon dioxide is fixed
in the sea each year (Steemann-Nielsen 1952), an
equal amount must be regenerated to keep the
system functional. As a general rule, the smaller
the organism, the faster is its metabolic rate. Approx-
imately 90 percent of the carbon dioxide produced
by respiration is formed by bacteria (Stanier et al.
1970). There are many mechanisms for both aerobic
and anaerobic production of ceirbon dioxide, and the
anaerobic means may have helped form the steady-
state carbon dioxide system on earth during the
Precambrian (Morita 1975).
Data have been accumulating concerning the
mineralization (respiration) of substrates during our
heterotrophic activity studies in the Arctic, and,
if we take into account data from the Antarctic,
the amount of carbon dioxide produced by these
processes could be considerable (Morita et al. 1974).
There appears to be a correlation between the PCO2
and carbon dioxide produced by microbes in the
upwelled waters off the Oregon coast. The pCOg
values in these waters are about 600 ppm, as a result
of oxidation of organic matter in water of interme-
diate depth (L. Gordon, Oregon State University,
personal communication). These high values are
partly caused by bacterial oxidation of sinking
organic matter. Our studies indicate that the amount
of carbon dioxide produced in this area by bacterial
action ranges from 1.52 X 10"^ to 9.0 X 10"^ /uM/hr
(Morita et al. 1974). In addition to the regeneration
effects of bacteria, they can also change the pH of
some environments, e.g., sediments, thereby affecting
the carbon dioxide system.
Particulate and dissolved organic carbon
Both particulate and dissolved organic carbon are
well discussed by Williams (1975) and Parsons
(1975). Organic matter in seawater is covered in
Hood (1970). Some of the compounds of lower
molecular weight (sugars, organic acids, and amino
acids) in the organic matter in seawater result from
microbial decomposition or fermentation of dead
marine plants and animals. Many of the end products
of decomposition and fermentation are dissolved
organic matter, including some of the ectocrine
compounds necessary for the growth of plants and
animals. In interstitial water of the sediments,
organic acids have been identified which are end
products of microbial fermentation. Bacteria, some-
times in large numbers, are associated with partic-
ulate organic material. These bacterial cells add to
the nutritive value of the particulate organic matter.
Particulate organic carbon has been shown to form in
the filtrates of seawater under experimental condi-
tions (Parson 1975). This process can also take
910 Microbiology
place with psychrophilic bacteria of seawater (Meyer-
Reil and Morita, unpublished data), and bacteria
can also be found with this reformed particulate
organic material.
In studies by Lott and Morita (unpublished data),
it was shown that when seawater was filtered through
a Whatman GF/C filter, 80 percent of the bacteria
in the seawater remained on the filter and 20 percent
passed through.
Tanoue and Handa (1979) studied the particulate
organic matter (POC) in the Bering Sea. They found
the carbon/nitrogen ratio of POC from surface
water to vary from 3 to 15/1; above the shelf the
ratio was 6.2-8.5/1. Since the carbon /nitrogen
ratio is lowest in bacterial cells, the question, from a
microbiological point of view, is how much par-
ticulate organic matter is microbial. Although these
investigators did find various amino acids in the
particulate matter, the microbial contribution to the
methionine could have been substantial. Amino
acids of the POC in deep water, as these authors
suggest, are derived from fecal pellets, but fecal
pellets are covered with bacteria. Methionine is
necessary for protein synthesis in all organisms (to
initiate transcription from the genome). It is also an
essential amino acid for higher organisms, including
the protozoa. Microbes have the enzymatic mecha-
nism to synthesize methionine.
According to Nishizawa and Tsunogai (1974), the
mean concentration of POC in the upper 50 m of
the Bering Sea ranges from 65 to 300 Mg C/1, with
the highest concentrations along the Aleutian chain.
This value is much higher than those found south of
this region. About two-thirds of this particulate
organic matter decomposes in the surface waters
(Nishizawa and Tsunogai 1974).
In the Nanaimo River estuary, Naiman and Sibert
(1978) have shown that the fluvial dissolved organic
carbon may be the greatest source of organic carbon
to the system. In the Norton Sound area the amount
of fluvial dissolved organic carbon added to the sys-
tem by the Yukon River has yet to be determined.
If this source of dissolved organic carbon is large,
then many bacterial cells may be supported by the
dissolved organic carbon, since bacteria are the most
efficient utilizers of dissolved materials.
Phosphates in seawater
As I said before, phosphates are readily taken up
by bacterial cells and released when the environment
becomes anaerobic. However, the production of
microbial phosphates acting on organic phosphates
must be considered. Alkaline phosphatase (enzyme-
catalyzed R-PO4 = H3PO4) activity does occur in
many marine bacteria. The question is how much
of the alkaline phosphatase is of bacterial origin.
Some phosphate is localized in the nucleic acids of
cells. Enzymatic action on the nucleic acids also
brings about the solution of phosphate. During rapid
growth of organisms, the acylation of an amino acid
to a transfer ribonucleic acid (tRNA) must be accom-
panied by the formation of adenosine monophos-
phate (AMP) from adenosine triphosphate (ATP),
liberating inorganic pyrophosphate. The action of
inorganic pyrophosphate in the marine environment
has not yet been considered.
If rapid decomposition of the particulate organic
matter in seawater occurs in the Bering Sea as indi-
cated by Nishizawa and Tsunogai (1974), then the
microbial mechanisms for liberating phosphate must
be considerable.
Inorganic nitrogenous compounds in seawater
The function of microbes in the nitrogen cycle
is well known, especially in relation to ammonia,
nitrite, nitrate, dinitrogen oxide, and nitrogen.
Ammonium oxidation and its relationship to the
cycling of nitrogen has been investigated in Skan Bay,
Unalaska Island, by Hattori et al. (1978). They
reported that ammonium oxidation to nitrite or
nitrate was occurring at a high rate below 35 m
in August 1972; but near the bottom water the
reduction of nitrate to nitrite and ammonium was
less intense. Unfortunately, the microbiology of this
situation was not studied.
BACTERIAL ACTIVITY IN RELATION
TO GEOLOGICAL PROCESSES
Bacterial activity in relation to geological processes
has not been the subject of intense investigation,
but it now appears that renewed interest has been
kindled. The diagenesis of sedimentary material
where sufficient organic matter is present occurs
mainly through the agency of bacterial action on the
organic matter, creating changes mainly in the Eh and
pH of the system. When the Eh is changed in the
sedimentary material, the sulfate-reducing bacteria
can produce sulfide, forming sulfide minerals of one
type or another. One of the main end products of
sulfate reduction in the marine environment is pyrite
(Howarth 1978). The process of pyrite formation,
once thought to be slow, is actually very rapid,
because of the copious amounts of hydrogen sulfide
produced by bacterial sulfate reduction when enough
energy is present. Calcite formation by bacterial
action can also be very rapid under anaerobic condi-
tions (Morita 1980). According to Suess (1979),
Microbiology 911
I
microbial decomposition of organic matter in recent
sediments of the Landsort Deep under anoxic condi-
tions resulted in tlie formation of a characteristic
assemblage of authigenic mineral precipitates of
carbonates, sulfides, phosphates, and amorphous
silica.
The gases identified in marine sediments are
oxygen, carbon dioxide, nitrogen, ammonia, hydro-
gen sulfide, methane, and dinitrogen oxide. Mechalas
(1974) discusses the various microbial processes of
forming these gases under aerobic and anaerobic
conditions. Nitrogen is the only one of the gases that
has been studied in the Bering Sea (Koike and Hattori
1979), and it has been considered only from a chemi-
cal point of view.
The most abundant gases released into the Norton
Sound area appear to be carbon dioxide and methane
(Cline and Holmes 1977, Kvenvolden et al. 1979,
Nelson et al. 1978). Although the seepage area
appears to produce mostly carbon dioxide, the
question still arises why it is not changed to methane
by microbial activity in that area, or why methane is
not the main source of carbon dioxide by bacterial
action. Much research needs to be done on the
microbiology of seep areas.
The production and use by microbes of the gases in
sediments are now being studied. Studies of the
consumption of nitrous oxide in an anoxic basin
(Cohen 1978), denitrification rates in situ (Oren and
Blackburn 1979), and ammonia turnover in sediments
(Blackburn 1979) have been published, and many
papers dealing with methane formation presented.
The diagenesis of sedimentary material is also of
great importance and the microbial contribution to
these processes still remains to be discovered. In
estuarine sands, microorganisms are able to pene-
trate into biotite and hornblende. Since they can
penetrate biotite more easily than hornblende, the
former is more rapidly weathered (Frankel 1977).
Early diagenesis of sedimentairy material in estuaries
is being studied by many investigators, but unfor-
tunately not the microbiology of the process. The
microbial population furnishes the catalytic force
to diagenesis by acting on the organic matter, pro-
ducing changes of the Eh, and to some extent the pH,
values. The pH and Eh dictate, to a large degree, the
type and magnitude of biochemical reaction that the
microbes bring about in the environment.
The regeneration of nutrients in sediments of the
Eastern Bering Sea warrants microbiological investi-
gation. Since this area is so productive, primary
nutrient generation is of prime importance. Accord-
ing to Hood and Reeburgh (1974), the abundant
supply of inorganic nutrients is due to the extensive
vertical mixing during winter and the influx of water
masses from the North Pacific. Vertical mixing of
sediments is considered responsible for the high
phosphate levels in Upper Klamath Lake, Oregon
(Harrison et al. 1972), where the microbes have
solubilized the inorganic phosphates. Since vertical
mixing during winter storms plays an important part
in supplying nutrients to the water column, the
microbial contribution to the regeneration process in
the sediments before and after a storm needs to be
investigated.
PRIORITIES FOR MICROBIOLOGICAL
RESEARCH IN THE EASTERN BERING SEA
When one considers the scope of the studies
needed and the vastness of the geographical area in
question, it is obvious that decisions about what
studies should be conducted will have to be made.
On the basis of microbiological data obtained in other
areas of Alaska (Lower Cook Inlet and the Beaufort
Sea), certain priorities can be recommended.
Background information for
making recommendations
During the past two years, studies have been
conducted on the effects of crude oil on microbial
function in sediments collected in both the Cook
Inlet and the Beaufort Sea. In sediments of both
areas it has been observed that crude oil interferes
with the transfer of organic nutrients from the
sediment into the food chain. These data suggest
that the presence of crude oil could seriously reduce
the productivity of a given area. Although these
studies have only been conducted for 18 and 8
months on Beaufort Sea and Lower Cook sediments
respectively, we hope to document the perturbation
over a period of time (the longer period of study is
recommended). Even after the above-mentioned
periods of time, significant differences in the various
parts of the carbon cycle have been observed. More-
over, the rates both of nitrogen fixation and of
denitrification are still greatly reduced in oil-per-
turbed sediments of the Lower Cook Inlet, even
after eight months' exposure.
Changes in pH and redox potential have been
observed in surface sediments perturbed by crude
oil. These changes would undoubtedly alter the
normal recruitment rates of benthic organisms into
affected areas. Increased rates of carbon dioxide
and methane production have been observed in
sediments into which crude oil has been introduced.
In summary, crude oil in marine sediments alters
microbial involvement in at least two mineralization
k
912 Microbiology
cycles; these alterations will in turn affect the bio-
logical productivity of the ecosystem.
Priorities
Of first importance is documenting the rates of
nitrogen and carbon cycling in the Bering Sea and
the impact of crude oil and crude oil dispersants
on these processes.
Shipboard studies
Surveys of microbial functions should be con-
ducted on board ship, using sediment and water
samples collected from different areas. During each
cruise, every effort should be made to coordinate
research efforts between investigators of different
but related disciplines.
The two areas of primary concern should be the
Norton Basin and the region north of the Aleutian
Islands to the Pribilof Islands and east to Bristol
Bay. From preliminary observations, these two
regions appear to represent contrasts in microbiolog-
ical activity and their differences should be more
completely documented to determine the potential
effects of crude oil production on microbial function
in these regions.
Studies should also be conducted in the Navarin
Basin, since this is also a potential lease site and a
region that might be transitional between the ex-
tremes represented by the Norton Basin and the
area north of the Aleutian Islands.
Routine measurements of microbial function
should be conducted in all study areas, but proc-
esses related to nitrogen fixation and denitrification
should be emphasized. Some studies to estimate the
bacterial biomass are needed.
Tray studies of oiled sediments
A minimum of four sets of eight to ten trays
should be placed at different locations in the Bering
Sea. One half of each set should be treated vidth
crude oil and the other half should be used as con-
trols. These trays should be placed in the Norton
Basin, near the Pribilof Islands, at the end of the
Alaska Peninsula near Unimak Island, and on the
north coast of Bristol Bay, for representative sam-
pling to determine the possible effects of crude oil in
various key locations.
Current effects studies have shown that semi-
annual sampling periods are sufficient to show
significant trends in altered microbial function. It
has also been shown that sediment samples kept
at in situ temperatures may be stored for up to 24
hours before they are processed without signifi-
cantly altering microbial function.
Routine observations should be made on these
samples with emphasis on nitrification and denitrifi-
cation processes.
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918 Microbiology
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Fish Diseases in the Bering Sea
B. B. McCain and W. D. Gronlund
Northwest and Alaska Fisheries Center
National Marine Fisheries Service
Seattle, Washington
INTRODUCTION
Very little definitive information was available
concerning the health of marine fish in Alaskan
waters before our OCSEAP-supported investigations
began in 1975. Turner (1886) reported observing
skin tumors (probably epidermal papillomas) on
starry flounder (Platichthys stellatus) and arctic
flounder (Liopsetta glacialis) in the Aleutian Islands.
In the early 1960's, Levings (1967) observed epi-
dermal papillomas on approximately 10 percent of
the rock sole (Lepidopsetta bilineata) in Bristol Bay
and the western Gulf of Alaska. Some of these skin
tumors covered almost half the body surface.
The purpose of the investigations discussed here
was to obtain data on the prevalence, distribution,
and characteristics of present diseases of demersal
fish in the Bering Sea. This effort required both
field and laboratory work. Field activities were
performed in cooperation with the Resource Assess-
ment and Conservation Engineering Division (RACE),
Northwest and Alaska Fisheries Center (NWAFC).
Animals captured by this agency as part of other
environmental assessment studies were examined
for externally visible pathological conditions. The
biological and pathological characteristics of each
affected animal were determined.
Since our investigation of the health of fish in the
Bering Sea began in 1975, five manuscripts describing
the results have been written: Wellings et al. (1977),
McCain et al. (1978), Alpers et al. (1977a and b),
and McCain et al. (1979).
METHODS AND MATERIALS
The study area in the Bering Sea was bounded
by 54° 41' to 58°46' N latitude and 168° 38' to
174°32'VV longitude. The sampling and data collec-
tion were carried out on the NOAA ship Miller
Freeman during the summer and fall of 1975 and the
spring and summer of 1976. Fish were captured with
an eastern otter trawl using procedures described by
Kaimmer et al. (1976). Trawls were made at depths
between 36 and 460 m.
Captured demersal fish were sorted according to
species, and subsamples were examined for externally
visible pathological conditions and, when feasible,
for readily recognizable internal disorders. For each
species in each haul, the number of animals exam-
ined, sex, and type of pathological condition were
recorded.
Animals with apparently abnormal conditions
were processed while still alive or freshly dead. Each
animal was assigned a specimen number, and the
following information was recorded: species, sex,
length, weight, method of age determination (otolith
or scale), pathological condition, and location and
size of the condition(s).
Photographs were taken of representative and
unusual pathological conditions. Fish samples were
preserved in 10-percent formalin with phosphate-
buffered saline. Specimens were also preserved in a
special fixative for electron microscopy. Sometimes
tissue was frozen at —20 C or in liquid nitrogen
(—196 C) for later microbiological procedures.
Bacteria or fungi inside lesions, tumors, and internal
organs were isolated by cauterizing the surface of
the tissue to be sampled, opening the tissue with a
sterile scalpel, removing an inoculum with a sterile
loop, and streaking the inoculum in petri dishes
containing bacteriological medium. Media used
included Ordal's Seawater Cytophaga Agar (OSCA),
brain-heart infusion agair (Difco,' dissolved in sea-
water), or potato dextrose ag£ir with penicillin and
streptomycin. In addition to streaking the inoculum
' Mention of commercial products is for information only and
does not constitute endorsement by tiie U.S. Department of
Commerce.
919
920 Microbiology
onto agar media, a portion of some inocula was
spread on a glass microscope slide and Gram-stained.
Representative colonies growing on the culture media
were purified by restreaking, stored in tubes contain-
ing OSCA, and returned to the laboratory for further
tests.
Laboratory activities involved processing the speci-
mens and the data acquired in the field. Tissue speci-
mens from animals with the main pathological con-
ditions to be examined histologically were matched
with the photographic colored slides showing the
gross appearance of the lesions.
Tissues to be examined by light microscopy for
histopathology were embedded in paraffin and
sectioned with a microtome, and the sections were
stained by a variety of methods, including hema-
toxylin and eosin, Oil-Red-0, Sudan black, and
Masson's trichrome. Microscopic examination of
sections taken from diseased tissue and major organs
makes it possible to determine abnormalities of
tissue structure, what types of cells are involved, and
whether or not intracellular or extracellular micro-
organisms are present.
Tissue which had been previously preserved in 2
percent glutaraldehyde and was to be examined
electron-microscopically was treated with osmium
tetroxide, dehydrated in absolute ethanol, embedded
in Spurs Low Viscosity Epoxy Resin, and sectioned
on an MT2B Dupon-Sorvall microtome. Sections
were examined with either a Ziess EM95 or an
AEI-EM801 electron microscope. Examination of
tissue in this manner makes it possible to detect
intracellular damage, identify disease-specific cells,
and observe virus particles.
Bacterial isolates were characterized using such
standard taxonomic criteria as cell morphology,
colony color and morphology, oxidase activity,
behavior in oxidation-fermentation media, and
motility.
RESULTS
Of the 29 species of fish examined in the Bering
Sea, 25 were free of recognizable pathological condi-
tions (Table 55-1). The affected species, associated
pathological conditions, and the average frequencies
of each condition were as follows: Pacific cod
(Gadus macrocephalus), pseudobranchial tumors,
8.7 percent, skin ulcers, 1.6 percent; pollock
(Theragra chalcogramma) , pseudobranchial tumors,
1.7 percent; yellowfin sole (Limanda aspera), lym-
phocystis, 2.8 percent; and rock sole, epidermal papil-
lomas, 1.3 percent (Table 55-2).
TABLE 55-1
Fish species captured in the Bering Sea in which no
detectable pathological conditions were identified
Agonus acipenseris (sturgeon poacher)
Anoplopoma fimbria (black cod, sablefish)
Atheresthes stomias (arrowtooth flounder)
*Careproctus sp. (snailfish)
Clupea harengus pallasi (Paciflc herring)
Dasycottus setiger (spinyhead sculpin)
*Eleginus gracilis (saffron cod)
*Hemilepidotus hemilepidotus (red Irish Lord)
Hippoglossoides elassodon (flathead sole)
Hippoglossus stenolepis (Pacific halibut)
Limanda proboscidea (longhead dab)
*Lumpenus sagitta (snake prickleback)
Lycodes palearis (wattled eelpout)
Mallotus villosus (capelin)
Microstomas pacificus (Dover sole)
*Myoxocephalus jaok
Myoxocephalus polyacanthocephalus (great sculpin)
Myoxocephalus sp.
*Osmerus mordax dentex (rainbow smelt)
Platichthys stellatus (starry flounder)
Pleuronectes quadrituberculatus (Alaska plaice)
Reinhardtius hippoglossoides (Greenland turbot)
Sebastes alutus (Pacific Ocean perch)
*Squalus acanthias (dogfish)
*Trichodon trichodon (Pacific sandfish)
* Fewer than 50 specimens were examined for this species.
The prevalence, distribution, and biological proper-
ties of affected fish and the histopathology of the
lesions are characterized below.
Pseudobranchial tumors of gadids
The gross appearance of the cod tumors has been
described by McCain et al. (1978) and Wellings et al.
(1977). Briefly, they were various shades of yellow,
pink, and brown. They were oval and smooth, ex-
tended into the pharyngeal cavity, and ranged in size
from just larger than the normal pseudobranch to 50
X 30 X 20 mm (Fig. 55-1). With one exception, all
the tumors were bilateral, and the two sides were
usually the same size. The tumors often had necrotic
areas on the surface, and there was normal-appearing
pseudobranchial tissue on the surface or in the
interior of each tumor.
The histopathological properties of the pseudo-
branchial tumors have been described previously
(Alpers et al. 1977b). Briefly, they included the
separation of normal-appearing pseudobranchial tis-
sue from the tumor tissue by a connective tissue
capsule and the presence of cells known as X-cells
(Fig. 55-2). These cells are also found in other
Fish diseases 921
TABLE 55-2
Prevalence of the major pathological conditions
of fish in the Bering Sea.
No.
No. and %
Species
Condition
examined
affected
Pacific cod
Pseudobranchial
4,654
403
Gadus
tumor
8.7
macrocephalus
Skin ulcer
4,654
73
1.6
Walleye pollock
Pseudobranchial
9,173
156
Theragra
tumor
1.7
chalcogramma
Rock sole
Epidermal
6,440
87
Lepidopsetta
tumor
1.3
bilineata
Yellowfin sole
Lymphocystis
8,036
228
Limanda aspera
2.8
marine fish tumors, and they will be discussed later.
In one cod with bilateral tumors, another similar
tumor was also found attached to a gill filament.
This tumor was oval, cream-colored, and about 4
mm in diameter (Fig. 55-3). The tumors had a
similar cellular organization, composed mainly of
X-cells (Alpers et al. 1977b), but no pseudobranchial
tissue was associated with the smaller gill tumor.
In the Bering Sea, 8.7 percent of the cod that were
examined had pseudobranchial tumors (Table 55-2).
"-a-
Figure 55-2. Photomicrograph of a section of a pseudo-
branchial tumor in a Pacific cod. Normal-appearing pseudo-
branch (P) is adjacent to tumor tissue (T). Typical X-cells
are identified by arrows. (Toluidine blue, X230.)
Tumor-bearing cod were most common in the south
central portion of the sampling area (Fig. 55-4).
Both the frequency of catches with tumor-bearing
cod and the proportion of fish affected decreased to
the northwest. Cod were not captured in the eastern
portion of the sampling area. The range of disease
frequency in hauls containing cod with tumors was
1.1-73.3 percent.
Analyses of the biological characteristics of tumor-
bearing cod from the Bering Sea showed that about
the same number of males as females had tumors.
The age composition of cod with tumors was dif-
ferent from that of normal cod ("normal," here and
for the other species described in this report, means
those apparently healthy animals captured, speciated,
sexed, measured, and, when possible, aged in 1975 or
1976 by the RACE Division and by us). Normal cod
ranged in age from one to five years, while no tumor-
bearing cod were less than two years old. In addition.
Figure 55-1. Bilateral pseudobranchial tumors (T) in the
pharynx of the Pacific cod.
Figure 55-3. Section of a secondar\' pseudobranchial
tumor (T) attached to the gill filament (G) of a Pacific
cod. (Hematoxylin and Eosin, X450.)
922 Microbiology
184°
182° 180°
178=
59'
58'
57=
56'
55'
54'
53°
52'
8/16 catches
50%
21/345 fish
6.1%
18/29 catches
62%
183/2282 fish
3%
187/1 554 fish
/ 1 2%
«.^.
>3 -'^
I L
J I I L_
J U
54°
53°
52°
180° 178° 176° 174° 172° 170° 168° 166° 164 162° 160° 158° 156°
Figure 55-4. The general distribution and frequencies of cod with pseudobranchial tumors in the Bering Sea.
tumor-bearing cod were about 25 percent shorter
than normal cod of the same age.
The pseudobranchial tumors of pollock and
cod were grossly similar in color, shape, and texture
(McCain et al. 1979) (Fig. 55-5). However, the
pollock tumors often protruded less, tending to
extend up into the roof of the pharynx, and unlike
cod, ten pollock had unilateral tumors. One pollock
was found to have on the outside of the operculum a
secondary tumor which had originated from an
invasive pseudobranchial tumor. In general, these
tumors were smaller than those of cod, ranging up to
35 X 20 X 10 mm.
The microscopic anatomy of these tumors was
much like that described for the same condition in
Pacific cod (Alpers et al. 1977b), with the following
exceptions: (1) granulomas common to Pacific cod
tumors were not seen in pollock; (2) the fibrous
stromata of the pollock tumors contained numerous
melanophores, whereas melanophores were seldom
observed in the stromata of Pacific cod tumors; and
(3) the pollock tumors, unlike Pacific cod tumors,
usually had a marked infiltration of macrophages and
lymphocytes.
In catches from the Bering Sea, 1 .7 percent of the
pollock had pseudobranchial tumors. Tumor-bearing
pollock were distributed in a pattern very similar to
that of cod with tumors (Fig. 55-6), with the widest
distribution and highest frequency in the south
central area. Of the hauls in which pollock were cap-
tured, 45 percent contained pollock with tumors,
and the disease frequency in these hauls was 0.6-
13.2 percent.
Figure 55-5. Bilateral pseudobranchial tumors (just above
card) in the pharyngeal fossae of a walleye pollock.
Fish diseases 923
78° 176° 174° 172° 170° 16B° 166° 164° 162° 160° 158° 156° 154°
59'
58°--
57°-
56'
55'
54'
53'
52'
180° 178°
Figure 55-6
176° 174° 172° 170° 168° 166° 164 162° 160° 158° 156°
The general distribution and frequencies of pollock with pseudobranchial tumors in the Bering Sea.
Skin lesions of Pacific cod
Two main types of skin lesions were observed on
Pacific cod: ulcers (Fig. 55-7) and ring-shaped lesions
(Fig. 55-8) (McCain et al. 1979). The ulcers were
roughly circular, ranged from approximately 1 to
50 mm in diameter, and were either pale white or
red (hemorrhagic), with a dark pigment concentrated
in the margin of the surrounding epidermis. Each
affected fish had between 1 and 40 ulcers. The
ring-shaped lesions were chairacterized by a cream-
colored strip 5-20 mm wide, sometimes with hemor-
rhagic foci surrounding a normal-appearing circular
Figure 55-7. Skin ulcers on the ventrolateral surface of
a Pacific cod.
Figure 55-8. Two ring-like lesions near the caudal region
of a Pacific cod.
924 Microbiology
patch of epidermis. These lesions were about 10-50
mm in diameter. Each diseased fish had 1-5 ring-
shaped lesions.
Histological examination of the skin ulcers revealed
that the epidermis was almost always absent from the
center of the lesion. Less often, portions of the
dermis had also been destroyed. The white cover-
ing over some ulcers was composed of residual
necrotic epidermis. The periphery of the lesions was
hyperemic, hemorrhagic, and contained numerous
inflammatory cells (lymphocytes and macrophages)
and areas of fibrosis (Fig. 55-9). Large numbers of
microorganisms were not observed histologically in
the ulcers (McCain et al. 1979). However, ulcers
from five different cod yielded Pseudomonas-like
bacteria, sometimes in pure culture, which, so far,
have appeared to be taxonomically identical.
The histological properties of the ring-like lesions
were described by McCain et al., 1979. Briefly, the
epidermis and the stratum spongiosum (a component
of the dermis directly beneath the epidermis) were
the only parts of the skin obviously affected by this
condition. The appearance of normal cod skin is
shown in Fig. 55-10. Cod epidermis normally con-
tains mucous cells and large cystic structures of
unknown function (Bullock and Roberts 1974).
In the epidermis of fish affected with the lesion were
large, cyst-like bodies, about four times the size of
a normal mucous cell, which contained a very baso-
philic center surrounded by an eosinophilic margin
(Fig. 55-11). Preliminary electron microscopic exam-
ination of these large, cyst-like bodies has demon-
strated the presence of herpes-like virus particles.
In the Bering Sea, 1.6 percent of the cod had
ulcers or ring-shaped lesions. Diseased cod were
*f\^:]i}~ -.^^-^ ..r-nj ,-i''-.
^j^^K •
»«
' Mcvu-
♦ i
¥■■-' ^W
^m ^ K
#* {
h :^
^^v#
W^^m
^¥-- ,
■••V *'
^^^^^^^^^K -
P'i '^
m
'wmi
Figure 55-10. Section of normal skin from a Pacific cod
showing epidermis (E) containing mucous cells (M) and
large cystic structures (CS). The normal-appearing dermis
(D) is also present. (Hematoxylin and Eosin, X250.)
found primarily in the south central area: here 5
percent of the fish were affected (Fig. 55-12). There
were no indications of sex, size, and age preference
in these conditions.
Epidermal papillomas of pleuronectids
The epidermal papillomas of rock sole from the
Bering Sea grossly and histologically resembled simi-
lar tumors described in several species of pleuro-
nectids along the western coast of North America
(McCain et al. 1978, Brooks et al. 1969, Wellings
Figure 55-9. Section of a skin ulcer on a Pacific cod.
Normal-appearing epidermis (E) is to the left, the ulcerated
area (U) is to the bottom, and the dermis surrounding the
ulcer has extensive hyperemia (h). (Hematoxylin and
Eosin, X250.)
Figure 55-11. Section of a ring-shaped skin lesion from a
Pacific cod demonstrating the basophihc bodies (P) and
large cystic structures (CS) in the epidermis. One baso-
philic body appears to be releasing its contents. (Hema-
toxylin and Eosin, X900.)
Fish diseases 925
184° 182° 180° 178° 176° 174° 172° 170° 168° 166° 164° 162° 160° 158° 156° 154°
"7 ' 7 ' 7 ' r-
59'
58°-
57»-
56" -
55°
54°-
53'
52'
51'
\ NUNIVflK-i
0/16 catches
0/345 fish
0%
iWIIBILOF IS
/
6/29 catches /
/ 21% 15/34 catches
15/2282 fish / 44%
-/ 0.7% 62/1554 fish (
-^ / 4% ^V
«!«SSC~S^~»^^^
^.^^
c^.
1 I I
180°
178°
176°
174°
172°
170°
168°
166°
164
162°
160°
158°
156°
Figure 55-12. The general distribution and frequencies of Pacific cod with skin lesions in the Bering Sea.
et al. 1967). The tumors ranged in size from 3 X
3X2 mm to 100 X 70 X 10 mm. They were brown
to black and elevated, with a papillary architecture
(Fig. 55-13). They were scattered at random on the
body surface and frequently extended to both sides
of a fish in such a way as to make the two sides
mirror images. No metastases were identified.
Examination of sections of epidermal papillomas
revealed the typical papillary structure of the thick-
ened layer of epidermal cells supported by a branch-
ing fibrovascular stroma (Fig. 55-14). Both the
stromal and epidermal areas had X-cells. Typical
X-cells are larger than normal epidermal cells, with
pale nuclei, large, intense nucleoh, and granular
cytoplasm.
/llll|nn!n:ml!'!'^''fn^^u^"v^
l"'^ l! ' 2 .-I ■«
n H 7!
I^I^9p *3- If
.. ^-v :
Figure 55-13. Rock sole with an epidermal papilloma on
its blind side.
Figure 55-14. Section from a rock sole epidermal papil-
loma showing typical X-cells (X), including some unusual
multinucleated X-cells. (Hematoxylin and Eosin,X100.)
926 Microbiology
Electron-microscopic examination of X-cells
showed that the cytoplasm contained numerous
vesicular bodies. The nucleus contained a single
large nucleolus, and the chromatin-like material was
evenly dispersed around the nucleus. This differed
from the normal-appearing cells in the tumors, which
had generally even-staining cytoplasm and a nucleus
with chromatin condensed around the periphery of
the nuclear membrane.
Tumor-bearing rock sole were found almost ex-
clusively in the south central part of the Bering Sea
(Fig. 55-15); their frequency was 1.3 percent.
Lymphocystis of yellowfin sole
Lymphocystis (a virus-caused disease) of yellow-
fin sole is characterized by the presence of growths
of various shapes and colors on fins and body surfaces
(Fig. 55-16). These growths, ranging from 1 mm in
diameter to 20 X 10 X 5 mm, were of three basic
types: (1) round, translucent bodies about 1 mm in
diameter, single or in clusters; (2) small red sacs on
the ends of fin rays; and (3) red-to-gray amorphous
growths. All these types had in common the presence
of small, round bodies— hypertrophied fish cells de-
scribed below. Fin erosion was associated with about
10 percent of the cases where lymphocystis growths
were on the fins (Fig. 55-16). Most growths were
found on the blind side of the fish.
The histological properties of lymphocystis
grov^rths have been extensively described elsewhere
(Alpers et al. 1977a, McCain et al. 1978, Russell
1974, Templeman 1965). The growths were com-
posed of hypertrophied cells about 0.1-1.5 mm in
diameter which contained cytoplasmic inclusion
bodies made up of hexagonal virions about 200 mm
in diameter (Fig. 55-17).
In the Bering Sea, 2.8 percent of the yellowfin
sole examined had this condition. Diseased yellow-
fin sole were found in almost all the catches in the
south central Bering Sea, and 10 percent of the
animals in this region were affected (Fig. 55-18).
In adjacent areas only 2 of 24 catches had fish with
this condition: the occurrence was less than 1
percent. About the same number of males as females
had this disease. The age composition of normal
yellowfin sole of both sexes was bimodal, with peaks
of abundance at six and eight years. The age compo-
sition of diseased fish closely paralleled that of the
normal population.
DISCUSSION
Both the prevalence and distribution of three
diseases— pseudobranchial tumors of cod, lympho-
cystis of yellowfin sole, and skin tumors of rock
sole— in the Bering Sea in 1975 (McCain et al. 1978)
168° 166° 164° 162° 160° 158° 156° 154°
59°^
58"
57'
56'
55'
54'
53'
52'
<=«=;^;~;__
„* t^
_L
_L
-52°
180° 178° 176° 174° 172° 170° 168° 166° 164 162° 160° 158° 156°
Figure 55-15. The general distribution and frequencies of rock sole with epidermal papillomas in the Bering Sea.
Fish diseases 927
were very similar to those we found in 1976 (McCain
et al. 1979). The 1976 incidences for the above
diseases were higher by 1.3, 0.7, and 0.3 percent,
respectively. In the two years, the distribution of
tumor-bearing cod and yellowfin sole with lympho-
cystis were almost identical. Rock sole with tumors
in 1975 appeared to be distributed in different
patterns from those found in 1976, but this deviation
Figure 55-16. Lymphocystis growth on the blind side
pectoral fin of a yellowfin sole.
184° 182°
180°
178° 176°
"T"
~r
174°
Figure 55-17. Electron micrograph of a lymphocystis
growth showing the hexagonal virions with area about 200
nm in diameter (X130,000).
172° 170° 168° 166° 164° 162° 160° 158° 156° 154°
59°
58° ~
57'
56'
55°
54'
53-
52°
51
0/8 catches
0/1068 fish
0/%
ADfiKI
/ / i
J I 1 1 L.
_1 1-
_i L.
52°
180° 178° 176° 174° 172° 170° 168° 166° 164 162° 160° 158° 156°
Figure 55-18. The general distribution and frequencies of yellowfin sole with lymphocystis in the Bering Sea.
928 Microbiology
may be explained by differences in the locations of
sampling stations. The stations sampled in 1975 and
1976 which had the highest frequencies of tumor-
bearing rock sole were the shallowest.
Previous studies of pleuronectids with epidermal
papillomas have shown that young flatfish between
six months and two years of age are most likely to
have tumors (Miller and Wellings 1971, Angell et al.
1975). Since young rock sole are first found near the
beaches and move into deeper water as they grow
older (Clemens and Wilby 1961), it is not surprising
that the shallow stations yielded the most tumor-
bearing rock sole. Our observations and those of
Levings (1967) demonstrated that tumors on older
fish can spread over as much as half the body surface,
including the head region. Extensive tumors and
other possible tumor-related conditions very Ukely
kill affected fish.
It was interesting in our study to discover that
three of the five diseases were unevenly distributed.
Yellowfin sole with lymphocystis, rock sole with
epidermal papillomas, and Pacific cod with skin
lesions were most prevalent in the southeastern
Bering Sea near Unimak Island.
The causes of only three of the pathological con-
ditions of demersal fishes found near the Bering Sea
shelf are known or suspected: lymphocystis of
yellowfin sole is caused by a virus, skin ulcers of
cod are apparently bacterially caused, and the ring-
shaped skin lesions of cod had herpes-like virus par-
ticles detectable by electron microscope. Pseudo-
branchial tumors (probably carcinomas) of cod
and pollock and epidermal papillomas of rock sole are
neoplasms of unknown cause. The two types of
tumors contained morphologically identical, tumor-
specific cells known as X-cells, suggesting a common
etiology. The origin of X-cells is not known, although
they could be either virally or chemically transformed
host cells or single-cell parasites.
Lymphocystis growths from yellowfin sole con-
tained apparently typical lymphocystis virus; if this
virus is similar to other lymphocystis virus isolates,
this disease may be infectious. If this is true, then
host defense mechanisms probably play an important
role in disease transmission. Therefore, environ-
mental stress (i.e., high temperature and pollution)
which affects the disease defenses could increase the
frequency of lymphocystis in yellowfin sole.
The types of pathological abnormalities so far
detected in the demersal fish populations of Alaska
are mostly chronic conditions. Chronic disease is
the main type of disease one would expect to find in
fish captured by the existing sampling methods,
because fish with chronic disorders live longer than
those with acute diseases. Acutely diseased fish,
infected with virulent bacteria or viruses, would be
rapidly removed from the population, either directly
by the disease or by predators. Therefore, the fish
diseases described in this report are probably not all
the diseases of these demersal fishes.
The research described in this report is relevant in
two main ways to an understanding of the effects of
petroleum development on marine animals in the
waters of Alaska's outer continental shelf regions.
The most important contribution is to provide data
on the present health of demersal fish and inverte-
brates before possible environmental effects of oil
drilling occur, so that future effects of oil on marine
animals can be assessed. Also, knowing the possible
causes of pathological abnormalities in demersal
animals will provide a clearer understanding of the
ways in which exposure of organisms to oil could
directly or indirectly affect the frequency and dis-
tribution of pathological conditions.
ACKNOWLEDGMENTS
Parts of the research reported here were performed
by Mark S. Myers, of the E.G. Division, and by Drs.
S. R. Wellings and Charles E. Alpers, of the Depart-
ment of Pathology, University of California (Davis).
We are particularly grateful to Linda Rhodes and
Ron Seifert for their technical assistance and to Dr.
Harold O. Hodgins for his advice and review of this
manuscript.
REFERENCES
Alpers, G. E., B. B. McCain, M. S. Myers, and
S. R. Wellings
1977a Lymphocystis disease in yellowfin
sole (Limanda aspera) in the Bering
Sea. J. Fish. Res. Bd. Can. 34:
611-16.
Alpers, C. E., B. B. McCain, M. S. Myers, S. R.
Wellings, M. Poore, J. Bagshaw, and G. J. Dawe
1977b Pathological anatomy of pseudo-
branch tumors in Pacific cod, Gadus
macrocephalus. J. Nat. Cancer
Inst. 54:377-98.
Fish diseases 929
Angell, C. L., B. S. Miller, and S. R. Wellings
1975 Epizootiology of tumors in a popula-
tion of juvenile English sole (Paro-
phrys uetulus) from Puget Sound,
Washington. J. Fish. Res. Bd. Can.
32:1723-32.
McCain, B. B., S. R. Wellings, C. E. Alpers, M. S.
Myers, and W. D. Gronlund
1978 The frequency, distribution, and
pathology of three diseases of
demersal fishes in the Bering Sea.
J. Fish. Biol. 12:267-76.
Brooks, R. E., G. E. McArn, and S. R. Wellings
1969 Ultrastructural observations on an
unidentified cell type found in
epidermal tumors of flounders. J.
Nat. Cancer Inst. 43:97-100.
Miller, B. S., and S. R. Wellings
1971 Epizootiology of tumors on flathead
sole (Hippoglossoides elassodon) in
East Sound, Orcas Island, Washing-
ton. Trans. Amer. Fish. Soc. 100:
247-66.
Bullock, A. M., and R. J. Roberts
1974 The dermatology of marine teleost
fish. I. The normal integument.
In: Oceanogr. Mar. Biol. 13:383-411.
Clemens, W. A., and G. U. Wilby
1961 Fishes of the Pacific Coast of
Canada. Fish. Res. Bd. Can. Bull.
68.
Kaimmer, S. M., J. E. Reeves, D. R. Gunderson,
G. B. Smith, and R. A. Macintosh
1976 Baseline information from the 1975
OCSEAP survey of the demersal
fauna of the eastern Bering Sea.
In: Demersal fish and shellfish
resources of the eastern Bering
Sea in the baseline year 1975,
157-366. NOAA, Nat. Mar. Fish.
Serv., Northwest and Alaska Fish.
Cent., Seattle, Washington.
Levings, C. D.
1967 A comparison of the growth rates
of the rock sole, Lepidopsetta
bilineata Ayres, in Northeast Pacific
waters. Fish. Res. Bd. Can. Tech.
Rep. No. 36.
McCain, B. B., W. D. Gronlund, M. S. Myers, and
S. R. Wellings
1979 Tumors and microbial diseases of
marine fishes in Alaskan waters.
J. Fish Diseases 2:111-30.
Russell, P. H.
1974
Lymphocystis in wild plaice Pleuro-
nectes platessa (L.), and flounder,
Platichthys flesus (L.), in British
coastal waters: A histo pathological
and serological study. J. Fish
Biol. 6:771-8.
Templeman, W.
1965 Lymphocystis disease in American
plaice of the Eastern Grand Bank.
J. Fish. Res. Bd. Can. 22:1345-56.
Turner, L. M.
1886
Results of investigations made
chiefly in the Yukon District and
the Aleutian Islands. In: Contribu-
tions to the natural history of
Alaska, U.S. Army.
Wellings, S. R., C. E. Alpers, B. B. McCain, and
M. S. Myers
1977 Fish diseases of the Bering Sea.
Annals N.Y. Acad. Sci. 298:290-
304.
Wellings, S. R., R. G. Chuinard, and R. A. Cooper
1967 Ultrastructure studies of normal
skin and epidermal papillomas of the
flathead sole. Zeitschrift fiir Zellfors-
chung 78:370-87.
Wellings, S. R., B. B. McCain, and B. S. Miller
1976 Epidermal papillomas in pleuronecti-
dae of Puget Sound, Washington.
Prog. Exp. Tumor Res. 20:55-74.
Section X
Plankton Ecology
John J. Goering, editor
I
Phytoplankton Distribution
on the Southeastern Bering Sea Shelf
J.J. Goering
University of Alaska
Fairbanks
R. L. Iverson
Florida State University
Tallahassee
ABSTRACT
Knowledge about the physical, chemical, and biological
factors important in regulating the spatial and seasonal distri-
bution of phytoplankton on the southeastern Bering Sea
continental shelf is reviewed.
The waters over the southeastern Bering Sea are highly
structured and consist of discrete domains divided by three
oceanographic fronts. Three stages of phytoplankton succes-
sion are applicable to these domains. The spring bloom of
stage-I phytoplankton, dominated by small diatoms of the
genera Chaetoceros and Thalassiosira and the colonial hapto-
phyte Phaeocystis poucheti, begins in April in the mid-shelf
and inner-shelf fronts and spreads from these loci across the
coastal, mid-shelf, and outer shelf domains. The bloom is
regulated mainly by the formation of the seasonal pycnocline
coupled with the spring deepening of the critical light depth.
The stage-II phytoplankton successional community is domi-
nated by medium-sized diatoms of the genera Chaetoceros,
Thalassiosira, Rhizosolenia, and Nitzschia, which remain in the
mid -shelf domain throughout late spring and early summer.
The stage-Ill successional group is totally dominated by
Rhizosolenia alata, which comprises over 90 percent of the
phytoplankton in some regions of the mid-shelf domain in
summer. Flagellates and dinoflagellates dominate the phyto-
plankton of the outer shelf domain during stages II and III of
the phytoplankton successional sequence. This is the conse-
quence of the removal of diatoms by the large calanoid cope-
pods and euphausiids which inhabit the outer shelf domain.
These large herbivores are confined to the outer shelf domain
by very low cross-shelf advection and the presence of the
middle front, which acts as a diffusion barrier. The mid-shelf
group of herbivores consists mostly of small zooplankton
which appear to be ineffective grazers of long-chain diatoms
such as Rhizosolenia alata. In the mid-shelf domain these large
diatoms are, therefore, not extensively grazed, and they sink
into the bottom water, where they support a well-developed
benthic food web.
933
INTRODUCTION
In addition to summarizing information about
Bering Sea phytoplankton distribution and seasonal
succession, we attempt here to identify the physical,
chemical, and biological factors important in regulat-
ing the spatial and seasonal distribution of phyto-
plankton on the southeastern Bering Sea continental
shelf.
Many investigators have reported the distribution
of phytoplankton during various seasons and in dif-
ferent Bering Sea regions, but little progress has been
made tovv^ard identifying the abiotic and biotic fac-
tors affecting the composition, succession, and
physiological state of Bering Sea phytoplankton
communities.
This treatment of Bering Sea phytoplankton is
almost totally limited to the communities on the
eastern continental shelf. This region is emphasized
because (1) it is unusually large, especially in w^idth
(Fig. 56-1), (2) it contains a large phytoplankton
biomass which supports a food web abundant in
commercially valuable pelagic and benthic species of
shell and finfish, birds, and mammals, (3) extensive
new knowledge relating to phytoplankton produc-
tivity, distribution, and seasonal succession has
appeared in the last few years from research con-
ducted by investigators supported by the U.S. Bureau
of Land Management, Outer Continental Shelf
934 Plankton ecology
^^
"1
B»WH|
1^3*
BERING SEA
"""""""■""■":..
■$>,^^ COASTAL DOMAIN |
P
■*
"""!/,
M /^'^y J
1
-
MID-
DOMAIN y^'^^^Kp
'-
OCEANIC DOMAIN
'''-, OUTER SHELF '''',
•%••-, DOMAIN
"^^ ,/
l<
Ite.
4«
Figure 56-1. PROBES study area, showing the fronts and
corresponding shelf domains.
Environmental Assessment Program (OCSEAP), and
the Processes and Resources of the Bering Sea Shelf
Program (PROBES), supported by the U.S. Na-
tional Science Foundation, and (4) it is a region of
the Bering Sea affected presently by human fishing
activities and potentially by oil exploration and
production.
DISTRIBUTION OF BERING SEA
PHYTOPLANKTON
The distribution of phytoplankton in regional
seas, such as the Bering, must be dealt with on scales
of hundreds as well as tens of kilometers. Differences
in plant populations in water separated by hydro-
graphic and geographic features must often be con-
sidered on a scale of hundreds of kilometers, whereas
the scale of 1-10 km is of interest in small water
patches influenced by local tidal and wind mixing,
insolation, and eddies with different water character-
istics (Steele 1976).
The collection of phytoplankton samples by
investigators studying the Bering Sea has provided
both qualitative and quantitative data. The sampling
techniques used have included vertical net hauls
extending from some depth below the euphotic
zone to the surface and collection of water from
discrete sampling depths. Identification techniques
have included filtration through various kinds of
cloth netting to collect phytoplankton and preserva-
tion of the phytoplankton with Lugol's solution.
Most recent studies have used either the settling
method or the centrifuge technique, which Phifer
(1934) introduced to Bering Sea studies. Table 56-1
lists the major Bering Sea phytoplankton studies
and the methods employed.
The studies of Bering Sea phytoplankton com-
pleted since the extensive review by Motoda and
Minoda (1974) have been centered in the eastern
Bering Sea. Saito and Taniguchi (1978) and Alex-
ander and Cooney (1979) have studied the ice and
shelf plankton of the eastern continental shelf.
Goering and Iverson (1978) and Iverson et al. (1979a
and 1979b) concentrated their efforts on the shelf
phytoplankton south of the Pribilof Islands and in
outer Bristol Bay.
Because phytoplankton are passively drifting or
only weakly swimming organisms, their life histories
are dramatically influenced by water circulation
patterns. Hughes et al. (1974) presented a compre-
hensive surface circulation scheme for the western
Bering Sea. Details of circulation on the eastern
continental shelf are discussed by Coachman and
Charnell (1977 and 1979) and Kinder and Schu-
macher (Chapter 5, Volume 1). The major surface
circulation features influencing phytoplankton dis-
tribution in the eastern Bering Sea are (1) the Alaska
stream, which flows westward along the Aleutian
Archipelago, with northward intrusion through var-
ious island passes, (2) a cyclonic gyre which domi-
nates the deep basin, (3) a 5-10 cm /sec westward
mean flow in the outer shelf domain, (4) an insignifi-
cant flow in the middle shelf domain, and (5) a mean
flow of 1-5 cm/sec counterclockwise in the coastal
shelf domain. The shelf circulation is dominated by
tides and wind mixing.
The major phytoplankton communities distributed
by these currents include (1) temperate-neritic com-
munities near the Aleutians and extending into inner
Bristol Bay, (2) a boreal-oceanic community within
the deep central basin and extending onto the eastern
continental shelf, (3) an arctic community near the
coasts of Siberia and Kamchatka, and (4) an ice
community associated with the seasonal ice.
Circulation over the southeastern Bering Sea
continental shelf
The growth of phytoplankton is critically linked to
water mixing: it regulates their exposure to light
and nutrients by controlling their vertical distribu-
tion as well as the supply of nutrients from deep
water. Water mixing and shelf circulation patterns
are important to understanding the distribution and
ecology of phytoplankton growing on the south-
eastern Bering Sea shelf.
The southeast Bering Sea is covered by a broad
(-500 km), shallow shelf (shelf break -170 m),
which has recently received extensive study by
investigators associated with the OCSEAP and
PROBES programs (Fig. 56-1). The waters of the
Phytoplankton distribution 935
continental shelf of this region are renowned for
large populations of shell and finfishes, birds, seals,
and whales, all species in higher trophic levels. The
early studies of the biology of this region of the
shelf were based on information that suggested a
cyclonic circulation pattern over the broad south-
eastern shelf; the concept was of a "river in the sea"
(somewhat analogous to the Atlantic Gulf Stream)
within which biological events in time and space
could be followed as the water moved downstream.
However, the physical oceanographic studies of
Coachman and his colleagues (Coachman 1978;
Coachman and Charnell 1977 and 1979; Kinder and
Schumacher, Chapter 5, Volume 1) provided the
first evidence that the "river in the sea" circulation
pattern was incorrect and a new conceptual model
of the shelf circulation was needed. These studies
provided hydrographic and current data which
showed that cyclonic circulation was so slow as to
be insignificant on a biological time-scale of days to
weeks, in comparison with other circulation pat-
terns. Instead, the shelf contains a well-developed,
relatively stable system formed by the interaction of
the waters of the open Bering Sea with those of the
shelf.
The waters over the southeastern Bering Sea shelf
are highly structured and consist of discrete domains
divided by distinct oceanographic fronts. A concep-
tual water circulation model used to direct PROBES
research is given in Fig. 56-2. Three fronts have
been found on this shelf, all approximately parallel
to the bathymetry. They occur where there is a
change in the lateral flux rates due to alterations in
water mixing energies and other topographic features
of the shelf (at least for spring through fall). The
shelf break front occurs in the upper 50 m over the
150- to 200-m depth zone. This front is separated
from the middle front by an outer shelf domain
PHYTOPLANKTON
SHELF BREAK
FRONT
OCEANIC
ZONE i OUTER SHELF Z
MIDDLE FRONT INNER FRONT
MIDDLE SHELF ZONE tCOASTAL ZONE
50
?^ 100
Q.
HI
Q
150
200
ALASKA STREAM/
BERING SEA WATER
^:::/;|:^.H.ELF w)^
yf \\ COASTAL
•vV Jy WATER
PROPERTY DIST.
; WIND MIXING
TIDAL MIXING
Figure 56-2. PROBES diagram showing cross-shelf fronts.
936 Plankton ecology
60-80 km wide with no frontal characteristics. The
Bering Sea/Alaska Stream water intrudes shoreward
as a bottom layer to the middle front. Above this
intrusion, but beneath about 30 m, the shelf water
moves offshore. Data of Coachman and Chamell
(1979) indicate that the surface and bottom waters
are separated (because of the depth of the outer
shelf domain) by a mid-depth region in which the two
water masses actually meet and mix by means of lay-
ering. This interleafing region is expressed as fine-
structure (1-10 m) instabilities in a layer beneath the
surface wind-mixed layer and above a bottom tidally
mixed layer.
The middle shelf front lies over the 100-m isobath,
and shoreward of this is a mid-shelf domain bounded
on the shoreward side by a third inner shelf front at
about 50 m. The mid-shelf domain covers a distance
of some 125-140 km, and because of the insignificant
flow in this domain, it has characteristics similar to
those of a lake. In the mid-shelf domain a strong
seasonal thermocline produces a two-layered water
column. Wind mixing from the surface can interact
with tidal mixing on the bottom, at least during
strong wind events, to cause some exchange between
the two layers. The bottom layer in this region is
cold and relatively rich in nutrients, a remnant of the
winter shelf waters. The shoreward edge of the
mid-shelf domain is bordered by the distinct inner
front which occurs over the 50-m isobath. Between
this inner front and the coast is the coastal water
domain. In this domain the water is shallow enough
for wind and tidal mixing to overlap, and the result is
a uniform water column. A mean flow of 1-5 cm/sec
directed towards the northwest also occurs here. The
circulation of the water on the shelf is dominated by
tides and wind events.
Shelf phytoplankton distribution
Several investigators have recently studied eastern
Bering Sea shelf phytoplankton (Saito and Taniguchi
1978, Alexander and Cooney 1979, Goering and
Iverson 1978, Iverson et al. 1979a and b). The major
efforts in these studies have centered around identi-
fication, standing crop determinations (chl a/1 and
cell numbers/1) and the role of biotic and abiotic
factors in regulating plant growth. Alexander and
Cooney (1979) used a cluster analysis technique to
analyze phytoplankton species composition from
over 109 stations in the eastern Bering Sea selected
to emphasize the ice-edge ecosystem. Iverson et al.
(1979a and b) concentrated on the spring phyto-
plankton bloom on the shelf south of the Pribilof
Islands.
The dominant species of phytoplankton found on
the eastern shelf of the Bering Sea are given in Table
56-1. Diatoms dominate the communities in most
regions and during most seasons. Microflagellates
and the chrysophyte Phaeocystis poucheti, however,
are in some regions and at certain times important
components of the phytoplankton community.
Microflagellates are reported to make up the major
portion of the phytoplankton populations in the
winter and early spring before the major diatom
bloom (Alexander and Cooney 1979). Phaeocystis
poucheti appears to be a regular feature of the outer
shelf and shelf-break region of the southeast Bering
Sea (Goering and Iverson 1978, Iverson et al. 1979a
and b).
Different investigators have reported somewhat
different species assemblages. This may result from
making collections during different stages of species
succession, since phytoplankton species dominance
can change in a few days or weeks. Distinct assem-
blages of eastern Bering Sea shelf phytoplankton are
associated with the ice, with the water column at the
ice edge, and with the ice-free water of the outer
and inner continental shelf.
The water associated with melting seasonal ice is
characterized by large numbers of pennate diatoms.
Many of these species probably also grow in seasonal
sea ice. Saito and Taniguchi (1978) classify 13 spe-
cies of diatoms as ice phytoplankton. Fragilaria
islandica, F. striatula, Nitzschia cylindrus, and N.
grunowii are reported to be dominant. Alexander
and Cooney (1979) also studied the species of phyto-
plankton in nonquantitative ice-core samples and in
the water column of the eastern Bering Sea. Many
species occurred both in the ice and water. Motile
littoral ice diatoms were often found in the water
even though they are not well adapted for pelagic
or neritic existence. Centric diatoms and chain-
forming pennate diatoms were also found in samples
of slush ice and solid sea ice. The ice plankton
apparently act as an important inoculum for the
first water-column bloom near the receding ice edge.
The Bering Sea ice-edge community characteris-
tically contains large numbers of chain-forming dia-
toms, many of which form flat ribbon-shaped colo-
nies (Alexander and Cooney 1979). Some of the
species are neritic centric diatoms, and others are
pennate ice plankton. The community is dominated
by Thalassiosira spp., but Nitzschia spp., Fragilariop-
sis spp., Achnanthes spp., Nauicula spp., Chaetoceros
spp., and Detonula spp. are also abundant numer-
ically. Other species also found at the ice edge in-
clude Nitzschia frigida, Bacteriosira fragilis, Parosira
glacialis, Gyrosigma spp., and Pleurosigma spp.
TABLE 56-1
Major Bering Sea phytoplankton studies (modified from Alexander and Cooney 1979)
Allen (1927)
Alien (1929)
Region
Dominant Species
Unimak Island
Chaetoceros debilis, C. scolopendra^ Thalassiosira
nordenskiotdii
Unimak Island Chaetoceros debilis, Skeletonema costatum
Spring
Spring and
Summer
surface water filtered
through silk bolting
cloth
surface water filtered
through silk bolting
cloth
Aikawa(1932)
Phlfer(1934)
Cupp(1937)
Motoda and
Kawarada{1955)
Marumo (1956)
Kawarada(1957)
Kawarada and
Ohwada(1957)
Karohji{1958.
1959)
Ohwada and Kon
(1963)
Bering Sea
Bering Sea,
Bering Strait
Chaetoceros atlanticus, C. criphilum, Corethron
hystrix, Rhizosoknia alala, R. hebetata f.
semispina, R. hebetata f. hiemalis, Thalassi-
othrix longissima
Denticula seminae, Stephanopyxis nipponica
Scotch Cap, Biddulphia aurita, Thalassiosira spp. especially
southern part of T. nordenskioldii, Chaetoceros sociolis, C.
Unimak Island debilis, Leptocylindrus danirus, Asterionella
japonica
Aleutian waters Chaetoceros spp.. Corethron hystrix, Denticula
sp., Nitzschia neriata, Rhizosolenia hebatata f.
semispina
S. of Kamchatka Chaetoceros convolutus, C. debilis, Corethron
Peninsula hystrix, Denticula sp., Nitzschia seriata
Bering Sea Chaetoceros conuolutus, C. compressus, C. debilis,
C. radicans, C. constrictus, Nitzschia clos-
terium, N. delicatissima, N. longissima, N.
seriata, Rhizosoknia hebetata f. semispina
Bering Sea Thalassiosira sp., Chaetoceros spp., Corethron
hystrix, Coscinodiscus oculus-iridis, Denticula
sp., Thalassiosira decipiens
Northern Bering Chaetoceros (subgenus Hyalochaete), Nitzschia
Eastern Bering seriata, Chaetoceros (subgenus Phaeoceros),
Chaetoceros concavicornis, Coscinodiscus sp..
Rhizosolenia hebetata f. semispina, C. atlanticus
Bering Sea Chaetoceros atlanticus, C. concavicornis, C.
conuolutus, C. compressus, C. constrictus, C.
debilis, C. decipiens, Corethron hystrix,
Denticula sp., Fragilaria islandica, Rhizo-
solenia alata, R. hebetata f. hiemalis, R.
hebetata f. semispina, Nitzschia seriata, N
closterium
Spring,
Summer, Fall
Spring
centrifugation and
settling
surface water
filtered through
fine mesh net
surface water and
vertical hauls
centrifugation
and settling
centrifugation
and settling
centrifugation
and settling
underway plankton
recorder with silk
bolting cloth net
concentrating
surface water
ICcells/m'
10* to lO'cells/m'
10* to lO'cells/m'
10* to lO'cells/m^
Zenkevitch
(1963)
Karohji (1972)
Motoda and
Minoda(1974)
Taniguchi et al.
(1976)
Saito and
Taniguchi (1978)
Alexander and
Cooney (1979)
Goering and
Iverson (1978);
Iverson et al.
(1979a, 1979b)
Northern Bering
Sea
Bering Sea
offshore waters
Bering Sea
Eastern Bering
Sea
Bering Strait
Eastern Bering
Sea
Southeastern
Bering Sea
Shelf
Chaetoceros (subgenus Hyalochaete). predominantly Summer
Chaetoceros farcellatus
Denticula seminae, Thalassiothrix longissima. Summer
Chaetoceros atlanticus, C. conuolutus, Coscino-
discus curvatulus, C. oculus-iridis, Nitzschia
seriata, Rhizosolenia hebetata f. hiemalis
Chaetoceros convolutus, C. concauicornis, C. Summer
debilis, C. compressus, C. radicans, C. didymus,
C. seiracanthus, C. furcellatus, C. constrictus,
Rhizosolenia hebetata f. hiemalis, Denticula
seminae, Nitzschia seriata, N. delicatissima, N.
longissima, Fragilaria sp., Thalassiothrix
longissima
Thalassiosira hyalina, T. nordenskioldii, Spring
Fragilaria, Nauicula
Ice phytoplankton: Fragilaria islandica, F. Summer
striatula, Nitzschia closterium, N. cylindrus,
N. grunowii
Spring phytoplankton: Thalassiosira decipiens,
T. grauida, T. hyalina, T. nordenskioldii
Summer phytoplankton: Chaetoceros convolutus,
C. debilis, C. furcellatus, C. subsecundus,
Dinoflagellates
Winter: Dinoflagellates, Thalassiosira sp.. Early spring
Chaetoceros sp.
Spring ice edge: Thalassiosira spp., Nitzschia
spp., Achnanthes spp., Nauicula pelagica, N.
vanhoffeni, Chaetoceros spp.. Detonula spp.
Shelf break; Chaetoceros debilis, C socialis,
C. compressus, C. radicans, Thalassiosira norden-
skioldii, Phaeocystis (dominant some years)
Middle shelf domain; Rhizosolenia alata. Spring
Chaetoceros debilis, Thalassiosira aestivalis,
Thalassiosira nordenskioldii
Outer shelf region: Phaeocystis poucheti
sedimented plankton
samples
vertical net hauls
Alaska coastal
area:
68x10'
cells/m'
surface water
Ix 10' to
and vertical net
1x10-
hauls
cells/m'
water samples at
discrete depths
water samples at
discrete depths
water samples at
discrete depths
water samples at
discrete depths
Eastern Strait
2.8x10* cells/1
Western Strait
4.6xl0*cells/l
10* -10' cells/1
Middle shelf
2-5x 10' cells/m»
Outer shelf
7-12xlO'cells,'m'
937
938 Plankton ecology
The dominant phytoplankton species of the ice-
free eastern Bering Shelf community varies with
season. During the early spring the high nutrient
waters of the mid-shelf domain contain dense popu-
lations of fast-growing small centric diatoms domi-
nated by species of Chaetoceros and Thalassiosira. In
late spring medium-sized long-chain-forming species
of Chaetoceros are abundant along with Rhizo-
solenia alata. In the outer shelf region Phaeocystis
poucheti is at times and in certain regions almost
totally dominant (Goering and Iverson 1978, Iverson
et al. 1979a and b).
SEASONAL SUCCESSION OF
EASTERN BERING SHELF PHYTOPLANKTON
Various models of the roles of abiotic factors in
determining the pattern of seasonal succession of
phytoplankton have been proposed. Dugdale (1967)
described the use of Monod equations to model the
kinetics of nutrient uptake and nutrient-limited
growth. His approach can be used to model the
successional changes in species by combining the
effects of various factors such as nutrients, light,
and temperature on growth of individual species.
Successional changes in species have been predicted
using this approach (Eppley et al. 1969), but in gen-
eral, such deterministic models which consider only
abiotic factors have met with little success. A num-
ber of complex biotic factors, such as predation and
sinking, apparently play important roles in phyto-
plankton succession.
Ambient nutrient concentrations undoubtedly af-
fect phytoplankton growth. Their role, however,
is still unclear (Goldman et al. 1979). Dugdale
(1967) suggested that ambient nutrient concentra-
tions might play an important role in phytoplankton
succession if each species had a different growth or
uptake rate when exposed to identical nutrient con-
centrations. Different half-saturation constants
(Kg) for uptake of nitrate and ammonium have been
reported for different species (see Parsons and Taka-
hashi 1973). The cell size of each species appears
to be correlated with K^ values. Eppley et al. (1969)
found that small diatoms, in general, have low Kg
values for nitrate and large diatoms have high values.
Oceanic species have been shown to have lower
Kg values than estuarine species (Guilleird et al. 1973)
and fast-growing species which tend to have smaller
cell size tend to have lower Kg values than larger
slow-grovdng species. The limited success of using
ambient nutrient content to predict phytoplankton
succession may result from the fact that Kg values
depend on temperature and nutrient stores within
cells (i.e., previous cell histories) as well as on am-
bient nutrient concentrations.
When there is no nutrient stress, nutrient uptake
shows a hyperbola-shaped response to light intensity
(Maclsaac and Dugdale 1972). It has been suggested
that nutrient /light relationships are important in
regulating species succession (Dugdale 1967, Eppley
et al. 1969). Half -saturation constants for light (Kjt)
can help to explain the interactions of light and
nutrients in controlling phytoplankton growth
in the euphotic zone (Maclsaac and Dugdale 1972).
Explaining the seasonal succession of phyto-
plankton by means of only chemical and physical
factors has met with limited success. Other biotic
factors such as selective predation, for example, can
favor the growth of certain species. Evolutionary
mechanisms which adapt phytoplankton to escape
predation include fast growth rate, large ceU size,
spines and other skeletal structures, and formation
of chains or large, odd-shaped gelatinous colonies (see
Munk and Riley 1952). We propose that selective
predation plays an important role in regulating the
grovid^h of certain phytoplankton in shelf waters of
the southeast Bering Sea.
Margalef (1958, 1962, 1967) was one of the first
to describe stages of phytoplankton succession.
Margalef's description of three stages of succession
was modified by Guillard and Kilham (1977). These
stages are applicable to the southeast shelf of the
Bering Sea. Before the spring bloom, dino flagellates
and Phaeocystis comprise most of the ceU numbers.
Many of the spring bloom formers are present in low
numbers (Fig. 56-3). Growth of stage-I phyto-
plankton begins when abundant nutrients and appro-
priate amounts of light are present. In the south-
east Bering Sea shelf environment, the accumulation
of nutrients during the winter coupled with the
spring increase in insolation triggers the blooming of
stage-I phytoplankton. The bloom begins in late
March or early April in the mid-shelf and inner-shelf
fronts, or near the seasonal ice edge if ice is present.
It begins in the fronts apparently when water column
mixing is reduced by the shift in the winter storm
pattern south of the Alaska Peninsula. The decreased
mixing, coupled with increasing spring solar radiation,
results in an average light intensity adequate for
rapid growth, a condition met when the critical
light depth exceeds the total depth of the water
column (Sverdrup 1953). The stage-I bloom spreads
across the mid-shelf domain and into the outer shelf
domain (Fig. 56-4), controlled primarily by forma-
tion of the mid-shelf seasonal pycnocline coupled
with the spring increase in the critical depth at which
light is adequate to support phytoplankton growth.
Phyloplankton distribution 939
The seasonal ice edge, when it extends over the
southeast Bering shelf, also appears to be important
in regulating the timing of the first spring water
column phytoplankton bloom (McRoy and Goering
1974, Alexander and Cooney 1979). Blooms prob-
ably first occur here because a seasonal pycnocline
develops at 10-25 m near the melting ice edge. The
reduction in depth of surface water column mixing
produces an environment with adequate light and
nutrients for rapid phytoplankton growth.
Blooms of algae within sea ice have also been
reported to add significant amounts of organic mat-
ter to regions covered by ice, particularly in shallow
coastal areas (McRoy et al. 1972, Clasby et al. 1976,
Alexander and Cooney 1979). Detailed discussions
of sea ice and ice-edge phytoplankton communities
and their roles in the annual cycle of primary pro-
duction in the coastal and northern seasonal ice-
covered Bering Sea are presented by Niebauer et al.
this volume.
The inorganic nitrogen content of water covered
with seasonal ice appears lower than in ice-free water
(McRoy and Goering 1974, Alexander and Cooney
1979). Ice may thus play some unknown role in
retarding winter nitrogen regeneration and perhaps
the regeneration of other nutrients, or else ice algae
may be more important consumers of winter water
column nutrients than is currently thought. If total
41 40 38
■ i
36 STATIONS 3^
• •
51
•
1
• • •
. 1
14
• •
5 Phaeocystis
20
/fff^'
m
60
■
J
"
^pnm^mmm,,,
■
^'
rjTTTTW
1/''
—
100
■
r
-
i
■
^^.r-rTrnTfTTf''
J'
f
-
H 140
0.
iij
o
.
mill \
_
180
■
1
-
n* Phaeocystis
-K
h
_ Prorocentrum >
3 14
8
-
7 1 1
T. nitzschioides i
7 3
1
7
220
R. alata
C. radiatus 1
C. curvatulus 1
~ T. aestivalis
3
^
*Number of
cells xlO /m ; water column
contains < 1 pg chl a/1
Figure 56-3. Prephytoplankton bloom, Leg I, 1978 R/V Thomas G. Thompson.
940 Plankton ecology
nutrient content is indeed lower in areas covered by
sea ice, then ice may actually lower the annual pro-
ductivity of these areas. Ice cover thus appears to
be much more important in regulating the seasonal
timing of phytoplankton growth than in enhancing
annual productivity.
Stage-I Bering Sea phytoplankton are adapted to
grow under conditions of low light, high nutrients,
and cold temperatures (Bering Sea surface tempera-
tures 1-3 C, NO3-N -20-25 mM, Si(OH'*)-Si -40-50
juM: see Goering and Iverson 1978, Iverson et al.,
1979a and b). These first-stage plants also seem to
escape heavy predation, although small zooplankton
such as Pseudocalanus spp. and Acartia longiremis
winter in the mid-shelf region as adults and must feed
on phytoplankton before reproducing (Cooney and
Geist 1978, Alexander and Cooney 1979). The
small diatoms of the genera Thalassiosira and Chae-
toceros dominate stage-I Bering Sea phytoplankton
numbers (Fig. 56-4). Total community cell division
STATIONS
62 64
rates are about 0.5 per day and cell densities reach
10^-10^/m^ (Goering and Iverson 1978, Iverson
et al. 1979b). Cylindropyxis temulens, Thalassio-
sira gravida, and Prorocentrum spp. have also been
reported as stage-I successional members (Alexander
and Cooney 1979). Phaeocystis poucheti in certain
regions, especially near the mid-shelf and outer shelf
fronts, also appears to be a stage-I species in the
Bering Sea (Fig. 56-4). Raymont (1963) has reported
that Phaeocystis grows well at high phosphate and
nitrate levels, a condition present in the Bering Sea
during stage-I successional development. Its growth
rate at cold temperatures has not been determined.
During the spring when Bering Sea temperatures
are low, the colonial haptophyte Phaeocystis com-
petes favorably with diatoms, and early in the spring
totally dominates the plant biomass in the near-
surface region of the shelf-break and middle shelf
fronts. Selective grazing of diatoms by larger zoo-
plankton (Calanus cristatus and C. plumchrus)
100 -
140 -
Figure 56-4. Phytoplankton
bloom, Leg II, 1979 R/V
Thomas G. Thompson.
180 -
220 -
260 -
Phytoplankton distribution 941
I
I
I
may be an important cause of the dominance of
Phaeocystis. Copepods have not been reported to
ingest the lairge mucilaginous colonies of Phaeocystis,
but green cell remnants of Phaeocystis were observed
in the guts and fecal pellets of Bering Sea euphausiids
of the genus Thysanoessa caught in surface waters
where Phaeocystis was abundant (Iverson et al.
1979b).
The stage-II phytoplankton successional communi-
ty in the middle shelf domain of the southeast Bering
Sea is dominated by medium-sized diatoms. The
major genera are Chaetoceros, Thalassiosira, Rhizo-
solenia, Nitzschia, and Phaeocystis; these persist
through mid- to late May (Fig. 56-5). The diatoms
form long chains and in some cases have long spines,
adaptations which may reduce predation. Only the
larger copepods of the outer shelf domain are capable
of effectively grazing these chain-forming diatoms;
the smaller middle-shelf copepods do not appear to
graze them. The stage-II group remains in the middle
front region and in the middle shelf domain through-
out late spring and early summer.
Flagellates and dinoflagellates dominate the phyto-
plankton of the outer shelf domain during stages
II and III of the phytoplankton successional sequence
(Figs. 56-4, 56-5). This may be the consequence of
diatom removal by the large calanoid copepods which
inhabit the outer shelf domain (Cooney, this volume).
Wind-mixing events in early summer transport new
nutrients to the photic zone in the Bering Sea as in
southeast Alaskan fjords (Iverson et al. 1974). An
example of the effects of this process is given in
Fig. 56-6, where vertical profiles before and after a
storm with a mean wind speed of 18 knots suggest
that total chlorophyll a increased by about 50 percent
in the water column after the storm. By mid-June
nutrients were below detection levels in the surface
layers of the middle shelf domain (Figs. 56-7, 56-8).
Nutrients are present in sufficient concentration in
the outer shelf domain as a consequence of grazing
control of phytoplankton productivity. In the middle
shelf domain, stage-II phytoplankton species which
are not grazed extensively sink to the bottom, where
they support a well-developed benthic food web
(Iverson et al. 1979b). By the end of June, most
of the middle-shelf domain surface layer is devoid
of nutrients, and stage-Ill phytoplankton species
which are able to grow under low nutrient conditions
replace stage-II species. The stage-Ill successional
group in the southeast Bering Sea is dominated by
Rhizosolenia alata, which is present in long chains.
Rhizosolenia alata comprised over 90 percent of
•=■ 100
k
120
140
160
180
200
2736
9
27
C. debile
C. concavicorne
C. decipiens
C. curvisetus
R. alata
T. aestivalis
N. delicatissima
C. hystrix
L. danicus
Phaeocystis
Flagellate
Prorocentrum
Gymnodium
59 157
67
287
107
28
45
98
56
169
82
20 77
55
280
13 181
25
63
26 27
3
14
6
6
21
14
3
588 6
7
13
9
21
*Number
of cells
xlO^/m^
Figure 56-5. Postphytoplankton bloom, Leg III, 1979 R/V Thomas G. Thompson.
942 Plankton ecology
a.
0)
o
STATIONS
177 176 175 174 173 172 171 170 169 168 167 166 165 164 163 162 161 160
E
£
a
4)
o
STATION DATE
• 2066 140579
♦ 2075 150579
1 1 1 1
Mg
chl a/m
1006
1459
20 30 40 50
ng chl a/I
10
Figure 56-6. Wind-mixing effects on the nitrate and
ciilorophiyU profiles on PROBES Leg II, 1979 R/V Thomas
G. Thompson.
total phytoplankton numbers at some middle shelf
domain stations during late June 1978. Evidence
from nitrogen-15 kinetic uptake experiments sug-
gests that regenerated nitrogen (ammonium and urea)
is the primary nitrogen source for stage-Ill phyto-
plankton species (Goering and Iverson, unpublished).
Apparently Rhizosolenia alata is capable of excelling
other phytoplankton species in taking up silicic acid
from very low ambient silicic acid concentrations and
of growing with only weakly silicified frustules.
Controversy exists over which ecological factors
are most important in determining the course of phy-
toplankton succession. Major arguments usually
center around the roles that ambient concentration of
nutrients, light regimes, and grazing play in the suc-
cessional changes observed in nature. In the shelf
domains of the southeast Bering Sea the patterns of
phytoplankton growth, biomass, and species composi-
tion appear to be very directly influenced by the dis-
80
E 100
f 120
Q.
Q 140
160
180
200
I ill I I I I I l_
SILICATE Oig-at/l)
PROBES 79 LEG 3
13-15 JUNE
_l I I I I 1 L.
Figure 56-7. Cross-shelf silicate distribution Leg III,
PROBES, 13-15 June 1979 R/V Thomas G. Thompson
(from Whitledge and Reeburg 1979).
tribution and abundance of oceanic and shelf herbi-
vores (Cooney and Geist 1978, Alexander and
Cooney 1979, Iverson et al. 1979b). Oceanic grazers
do not invade water shoreward of the middle front
(Fig. 56-2). They are confined to the outer shelf
domain because of the hydrographic conditions
which do not allow the extensive exchange of oceanic
water with mid-shelf water. The oceanic group is
composed of euphausiids and large calanoid copepods
which winter in deep water beyond the shelf break
and which move into the surface waters of the outer
shelf domain in spring to feed on the spring phyto-
plankton bloom. These animals are able to graze on
large phytoplankton, including the large chain-forming
diatoms, and some, especially the euphausiids, also
may graze on Phaeocystis. The shelf herbivore group
consists mostly of small zooplankton such as Pseudo-
calanus spp. and Acartia spp., which are year-round
residents. They overwinter as adults and reproduce
and develop large populations after the first spring
phytoplankton bloom. Experimental evidence sug-
STATIONS
177 176 175 174 173 172 171 170 169 168 167 166 165 164 163 162 161 160
80
•g 100
f 120
Q.
□ 140
160
180
200
220
Figure 56-8. Cross-shelf nitrate distribution. Leg III,
PROBES, 13-15 June 1979 R/V Thomas G. Thompson
(from Whitledge and Reeburg 1979).
Phyloplanklon distribution 943
gests that these animals are ineffective grazers of
l£irge chain-forming diatoms which dominate the
phytoplankton in most domains of the southeast
Bering Sea shelf. These two different zooplankton
communities produce an across-shelf differential
grazing stress which significantly influences the de-
gree of coupling between phytoplankton produc-
tivity and pelagic herbivores, and alters the seasonal
succession of phytoplankton in the two shelf do-
mains. The oceanic grazers which are confined to
the outer shelf domain heavily graze large chain-
forming diatoms, and thereby regulate their standing
crop. This grazing activity and regeneration of
nutrients within the euphotic zone by the excretory
processes of zooplankton reduces the rapidity with
which nutrients are depleted. This high rate of
nutrient resupply prolongs the spring phytoplankton
bloom and the first two stages of species succession
in the outer-shelf domain, by comparison with the
mid -shelf domain.
In the mid-shelf domain the smaller zooplankton
are unable to effectively graze large diatoms, which
thus flourish, grow without grazing control, and more
rapidly consume all nutrients, leading to a more rapid
phytoplankton species succession in this shelf zone.
Much of the phytoplankton biomass is not consumed
in the water column and is free to sink to the sea bed,
where it supports a rich benthic food web. Several
important commercial species such as king and Tanner
crabs and yellowfin sole are important members of
this Bering Sea benthic food web. The mid-shelf
sediments have been shown to be richer in animal
biomass than the inner and outer shelf sediments
(Haflinger 1978).
ACKNOWLEDGMENT
Much of the phytoplankton research described
in this chapter (Contribution No. 426, Institute of
Marine Science, University of Alaska, Fairbanks)
was conducted by personnel of the PROBES pro-
gram, which is funded by the National Science
Foundation, Division of Polar Programs, under grant
No. DPP 7623340 to the University of Alaska.
Alexander, V., and T. Cooney
1979 A quantitative study of the phyto-
plankton from the eastern Bering
Sea. In: Environmental assessment of
the Alaska continental shelf, NOAA/
OCSEAP, Ann. Rep.
Allen, W. E.
1927 Surface catches of marine diatoms and
dinoflagellates made by U.S.S. Pioneer
in Alaskan water in 1923. Bull.
Scripps Inst. Oceanogr. Tech. Ser.
l(4):39-48.
1929 Surface catches of marine diatoms
and dinoflagellates made by U.S.S.
Pioneer in Alaskan waters in 1924.
Bull. Scripps Inst. Oceanogr. Tech.
Ser. 2:139-53.
Clasby, R., V. Alexander, and R. Homer
1976 Primary productivity of sea-ice algae.
In: Assessment of the Arctic marine
environment: Selected topics, D. W.
Hood and D. C. Burrell, eds., 289-
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Coachman, L.
1978 Water circulation and mixing in the
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C. P. McRoy, ed., 1-116. Univ. of
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Coachman, L., and R. Charnell
1977 Finestructure in outer Bristol Bay,
Alaska. Deep-Sea Res. 24:869-89.
1979 On lateral water mass interaction—
a case study, Bristol Bay, Alaska.
J. Phys. Oceanogr. 9:278-97.
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1963 A microplankton survey as a contribu-
tion to the hydrography of the North
Pacific and adjacent seas. 2. Dis-
tribution of the microplankton and
their relation to the character of
water masses in the Bering Sea and
northern North Pacific Ocean in
the summer of 1960. Oceanogr.
Mag. 14:87-99.
Parsons, T., and M. Takahashi
1973 Biological oceanographic processes.
Pergamon Press, Oxford.
Phifer, L. D.
1934
Raymont, J.
1963
The occurrence and distribution of
planktonic diatoms in the Bering
Sea and Bering Strait, July 26-August
24, 1934. Rep. Oceanogr. Cruise
U.S. Coast Guard Cutter Chelan,
1934. Part 11(A): 1-44.
Plankton and productivity in the
oceans. Pergamon Press, London.
Saito, K., and A. Taniguchi
1978 Phytoplankton communities in the
Bering Sea and adjacent seas. II.
Spring and summer communities in
seasonally ice-covered areas. Astarte,
11:27-35.
Steele, J. H.
1976 Patchiness. In: The ecology of the
seas, D. H. Gushing and J. J. Walsh,
eds. N. B. Saunders Co., Philadelphia.
946 Plankton ecology
Sverdrup, H.
1953
Taniguchi, A.
1976
On conditions for the vernal blooming
of phytoplankton. J. Cons. Explor.
Mer 18:287-95.
K. Saito, A. Koyama, and M. Fukuchi
Phytoplankton communities in the
Bering Sea and adjacent seas. I.
Communities in early warming season
in southern areas. J. Oceanogr. Soc.
Japan 32:99-106.
Whitledge, T. E., and W. S. Reeburg
1979 Nutrient dynamics and distribution
in the Southeast Bering Sea. PROBES
Prog. Rep. 1979. Inst. Mar. Sci.,
Univ. of Alaska, Fairbanks.
Zenkevitch, L. A.
1963 Biology of the seas of the U.S.S.R.
Interscience Pub., New York.
i
Bering Sea Zooplankton
and Micronekton Communities
with Emphasis on Annual Production
R. Ted Cooney
Institute of Marine Science
University of Alaska
Fairbanks
ABSTRACT
Zooplankton and micronekton distributions, abundance,
and production are reviewed for the Bering Sea. Regional
differences in community composition are related to water
mass characteristics and large-scale hydrographic patterns.
A listing of both holoplankton and micronekton includes
341 species.
The distribution of biomass varies with season and location.
A narrow band of large standing stocks of calanoid copepods
Calanus plumchrus, C. cristatus, and Eucalanus bungii bungii
occurs regularly during the late spring and early summer
along the shelf break of the southeast Bering Sea. Quanti-
ties approaching 200 g wet weight/m^ are reported.
New and published estimates of zooplankton production
are compared for the Bering Sea and several subunits of it.
Direct measures of community particle ingestion converted
to carbon production indicate that the oceanic region pro-
duces about 13 g C/m^ /yr, the shelf-break community 33
g C/m^ /yr, the mixed community 8 g C/m^ /yr, and the
middle-shelf and coastal community between 2 and 6 g C/m^ /
yr-
The trophic implications of partitioning the secondary
production in the water column in this manner are discussed
in terms of exchange with higher trophic levels.
INTRODUCTION
Motoda and Minoda (1974) have summarized
much of the Japanese and Soviet Uterature describ-
ing zooplankton and micronekton communities in
the Bering Sea. This review includes papers and
manuscripts by Anraku (1954), Vinogradov (1956),
Nishio (1961), Kawamura (1962), Koseki (1962),
Morioka (1963), Yamazaki (1963), Omori (1965),
Matsumura (1966), Minoda (1958, 1971), Nemoto
(1956, 1962, 1963), and Zenkevitch (1963). These
contributions have been used to illustrate large-
scale features of the distribution of the unobtrusive
pelagic fauna of this northern sea.
Three generally recognizable copepod groupings
have been suggested as characteristic of water masses
defining the upper 200 m of the Bering Sea: (1) an
oceanic assemblage dominated by the interzonal
seasonally migrating copepods Calanus cristatus,
C. plumchrus, and Eucalanus bungii bungii, often
accompanied by Metridia pacifica (= lucens); (2) an
inner eastern shelf community represented by Calanus
glacialis and Acartia longiremis in the south and
Eurytemora herdmani, Epilabidocera amphitrites,
and Tortanus discaudatus over the northern shelf;
and (3) a mixed community around the transition
between oceanic and shelf waters along the eastern
shelf break (Fig. 57-1). The distributions of several
common euphausiids and amphipods are also cited
as being correlated with the general structure of the
major water masses (Nemoto 1962, Fukuchi 1970,
Taniguchi 1972).
This description, particulcirly the distribution of
copepods, is similar to a pattern attributed to Vino-
gradov (in Zenkevitch 1963), who lists four major
faunal assemblages in the Bering Sea (Fig. 57-2).
This earlier account also explains the strong resem-
blance of zooplankton distributions over the northern
shelf to those in the oceanic region as resulting
from transport of deep-water plankters by the north-
ward flow of water across the shelf south and west
of St. Lawrence Island, through the Bering Strait,
and into the Chukchi Sea.
These generalized large-scale patterns, based on
several hundreds of observations, represent gross
near-surface zooplankton distributions during the
summer or ice-free months of each year. However,
in themselves, these patterns cannot be used to
evaluate the functional dynamics of zooplankton
communities except in the most general sense.
947
948 Plankton ecology
170°W
- 60° N
- 50° N
Figure 57-1. Large-scale distributions of copepod indicator species in tiie Bering Sea (from Motoda and Minoda 1974).
Geynrikh (1968) and Vinogradov and Arashkevich
(1969) describe the role of the large herbivorous
oceanic copepods in the northeast and northwest
Pacific Ocean. The reproductive strategy of these
species is cited as the principal mechanism promoting
close interaction between the grazing community
and the early spring plant stocks. Indeed, Parsons
(1965) notes that because of the efficiency of this
strategy (adults overwintering and reproducing in
late winter without first having to feed), grazers in
the form of young copepodids are present in great
numbers at the time conditions become stabilized
for the spring phytoplankton bloom, or before.
In the resulting closely coordinated system, the
bloom manifests itself at the level of primary con-
sumers rather than producers. It is assumed that a
similar relationship holds in the Bering Sea for the
oceanic community composed of these same species.
Even though the Bering Sea is the most productive
region in the North Pacific Ocean (Bakkala and
Smith 1978), there is little information on zoo-
plankton production here. Ikeda and Motoda (1978)
report respiratory, grazing, and growth requirements
for zooplankton in four large areas of the Bering Sea
and in waters south of the Aleutian chain, but only
for summer stocks.
The most recent U.S. studies of zooplankton and
micronekton have been undertaken either in areas
proposed for offshore petroleum development or
those presently under heavy fishery exploitation, or
both (Cooney 1976, 1977, 1978, 1979; Alexander
and Cooney 1979). The oil-related investigations
were funded by BLM/NOAA as simple baseline
characterizations, whereas Processes and Resources of
the Bering Sea Shelf (PROBES) studies were initiated
to describe the trophic efficiency of outer Bristol
Bay. Within the framework of PROBES, multidis-
ciplinary questions were asked about seasonal and
spatial variations in the composition of animal
plankton and micronekton communities, and rates
of secondary production were measured relative to
the physical structure of the water (fronts and
inter-frontal domains) and the timing of the annual
production cycle.
This chapter reviews previous studies and summa-
rizes the results of work conducted in the southeast-
em Bering Sea from May 1975 to June 1979 aboard
the NOAA vessels Discoverer, Miller Freeman, and
Zooplankton and micronekton communities 949
170°W
160°E
- 60°N
- 50° N
ZOOPLANKTON COMMUNITIES
South Bering Sea Group — Calanus cristatus, C. tonsus {= plumchrus), Eucalanus bungii bungii, Racovitzanus antarc-
ticus, Scolecithricella minor, Parathemisto japonica, and Oncaea borealis.
^ North Bering Sea Group —Calanus finmarchicus (probably C. glacialis), Parathemisto libellula.
West Neritic Group — Podon leuckarti, Centropages mamurrichi, Acartia clausi, and A. longiremis.
East Neritic Group — same as West Neritic Group.
Figure 57-2. Large-scale distributions of zooplankton communities in the Bering Sea (from Zenkevitch 1963).
Surveyor, and the University of Alaska research
vessels Acona and Thomas G. Thompson. Zooplank-
ton and micronekton were sampled with a variety of
nets, including 60-cm bongo, 1-m ring, and 2-m NIO
trawl. The 1-m net (0.333 or 0.202 mm Nitex) was
generally fished vertically between the seabed and
the surface or, at deeper locations, from 200 m to
the surface. The bongo-net (0.333 or 0.505 mm
Nitex) and NIO trawl (3.0 mm nylon) collected
organisms in open double oblique tows. The former
was always equipped with digital flowoneters to
measure volumes filtered and a time-depth recorder
to monitor the maximum depth of the sample;
although most samples were taken from the upper
100 m, the 2-m trawl was occasionally fished deeper
than 500 m. Several hundred samples were processed
to provide lists of species and determine the abun-
dance of plankton organisms at various times and
locations. The work sponsored by BLM/NOAA
addressed distributional properties in four subareas
of outer Bristol Bay defined bathymetrically (Fig.
57-3). These were identified as: (1) open ocean
(depths greater than 200 m); (2) outer shelf (depths
between 100 and 200 m); (3) central shelf (depths
between 50 and 100 m); and (4) northern coastal
(depths less than 50 m). A somewhat similar scheme
was adopted by PROBES, although the strata were
differentiated by frontal systems exhibiting con-
siderable consistency throughout the season (Iverson
etal. 1979a) (Fig. 57-4).
950 Plankton ecology
Figure 57-3. The area of sampling and its division into
bathiymetric domains.
The estimates of secondary production presented
here are taken from the literature and current un-
published experimental studies in the southeast
Bering Sea. (See Appendix 57-III for a discussion of
methods and limitations of the author's direct meas-
urements of particle ingestion and calculations of
carbon growth production.)
Of this total, 22 species and 3 generic composites
were found to be numerically common (Table 57-2;
Appendix 57-11). An even smaller number of taxa
are known to make up 90 percent or more of the
animal plankton biomass in this region (Vinogradov
1968, Zenkevitch 1963).
Three groups of zooplankton are found consis-
tently in hydrographically defined domains in the
southeast Bering Sea (Fig. 57-5). These are: (1) an
oceanic and outer-shelf community composed of the
interzonal copepods Calanus cristatus, C. plumchrus,
and Eucalanus bungii bungii, with Metridia pacifica
(= lucens); Oithona similis and Pseudocalanus spp.
are also present. The a.mphipod Parathemisto pacifica,
the chaetognaths Sagitta elegans and Eukrohnia
hamata, and the euphausiids Thysanoessa longipes
and T. inermis are the other common indicator
species in this regime; (2) a middle-shelf and coastal
community dominated by the small copepods Acartia
TABLE 57-1
Summary of zooplankton and micronekton species
diversity by major taxa for the Bering Sea
COMMUNITY COMPOSITION
In all, 251 species and 6 composite genera repre-
senting 20 major taxonomic categories were sorted
from samples taken in the eastern Bering Sea from
May 1975 through June 1977 (Appendix 57-1).
Meroplanktonic forms and holoplankton are com-
bined. This listing supplements the summary pub-
lished by Motoda and Minoda (1974) by 169 species;
most additions are to Amphipoda, Hydrozoa, Deca-
poda, and Teleostei (Table 57-1). The most diverse
group is the Copepoda.
BERING SEA
"',„ ?■'„ COASTAL DOMAIN
''"'"■•;„„ = '""orli'''--,, .0.=..,,..'
f
^
"■'"""'J^"' ^^1
^
">""«'«;t,'.'^" .ita^H
/"
**
"""'ft'Ofl'/ "'^"S"''K';,.yi{,u*'" o^'' ^kK^
C... L,0«.0.,CH ^^HDF
i
^gC-^^f^^
nilTFB F ^f^Sr *
'S'4'V DOMAIN '>«>«iiN«,. ^m^*^^
OCEANIC DOMAIN
'%. / ^tfW-':..Ef\
^^^-^-Sj. ............
**■-,.:•""
H^
Figure 57-4. Frontal and interfrontal regions defined by
the physical oceanography of the southeast Bering Sea
(from Iverson et al., 1979a).
1
dumber of species^
BLM/NOAA
Motoda and
1975-77
Taxon
Minoda (1974)
Additions
Total
Hydrozoa
1
20
21
Scyphozoa
10
0
10
Siphonophora
10
0
10
Ctenophora
1
0
1
Mollusca
2
6^
8
Polychaeta
1
le*^
17
Chaetognatha
6
0
6
Copepoda
110
1
111
Cladocera
2
2
Amphipoda
6
61
67
Cumacea
8
8
Ostracoda
7
7
Euphausiacea
7
0
7
Isopoda
2
2
Mysidacea
16
4
20
Nebaliacea
1
1
Decapoda
IS''
13
Appendicularia
2
0
2
(larvacea)
Cyclostomata
1
1
Teleostei
27''
27
TOTAL
172
169
341
^Generic composites not included.
''Includes meroplanktonic forms.
Zooplankton and micronekton communities 951
longiremis, Pseudocalanus spp., and Oithona similis,
supplemented by lesser numbers of Calanus glacialis
and C. marshallae. The amphipod Parathemisto
libellula, the chaetognath Sagitta elegans, and the
euphausiid Thysanoessa raschii are the other common
TABLE 57-2
Commonly occurring representatives of zooplankton
and micronekton communities in the southeast Bering Sea
Cnidaria
Hydrozoa
Aglantha digitate
Coryne principes
Scyphozoa
Chrysaora melanaster
Cyanea capillata
Annelida
Polychaeta
Typholoscolex mulleri
Mollusca
Gastropoda
Clione limacina
Limacina helicina
Chaetognatha
Eukrohnia hamata
Sagitta elegans
Arthropoda
Copepoda
Acartia longiremis
Calanus cristatus
C. glacialis
C. marshallae
C. plumchrus
Eucalanus bungii bungii
Metridia pacifica (= lucens)
Oithona similis
Pseudocalanus spp.
Cumacea
Diastylis bidentata
Amphipoda
Parathemisto libellula
P. pacifica
Decapoda
Chionoecetes spp.
Euphausiacea
Thysanoessa inermis
T. longipes
T. raschii
Chordata
Larvacea
Oikopleura spp.
species; and (3) a nearshore community associated
with the brackish coastal lagoons and estuaries.
The copepods Acartia clausi, Pseudocalanus spp.,
Centropages abdominalis, Eurytemora pacifica, E.
herdmani, and Tortanus discaudatus and the clado-
cera Podon and Evadne are characteristic fauna in
this shallow-water environment. Between the rela-
tively stable middle-shelf water and that of oceanic
origin, the zooplankton community becomes a
mixture of shelf and oceanic species.
This spatial partitioning of the zooplankton and
micronekton communities is maintained by the
presence of an oceanographic front which parallels
isobaths between 100 and 80 m (Iverson et al. 1979a).
The front acts as a barrier restricting the advective
exchange of oceanic and shelf waters, and as a result,
oceanic zooplankton are unable to penetrate the
middle shelf in any abundance. In the relatively
isolated middle-shelf domain from the 80-m front
landward to about 50 m, massive phytoplankton
blooms with high volumes of organic particulates
occur for several weeks each year. Although the
small copepods Acartia, Pseudocalanus, and Oithona
occur abundantly in this domain (10^ -10"* /m^ ), they
apparently do not control the growth of phyto-
plankton (Cooney and Coyle, in preparation). These
species overwinter in moderate abundance and must
first feed before reproducing. Since the middle-
shelf water mass is cold in the early spring (usually
< 1 C), the generation time for populations of these
copepods responding to increased food is 1-2 months,
and the lag period between the initiation of the
bloom and an abundance of grazers is longer than
normal. The early spring plant populations grow
rapidly under relaxed grazing stress. As the season
progresses, vertical mixing caused by storms, along
with tidal exchange, promotes nutrient recycling
so that the bloom is protracted. This is particularly
true at the 80-m front and along the shelf break,
where chlorophyll a is present from April through
September (Iverson et al. 1979b).
BIOMASS DISTRIBUTION AND
SEASONAL ABUNDANCE
Motoda and Minoda (1974) report summer bio-
mass values (wet wt. g/m^ ) for zooplankton sampled
on a five-degree grid in the Bering Sea over a 15-
year period. In the region east of 180°, the oceanic
community averages 35.5 g/m^ , over the southern
shelf (< 200 m) 52.2 g/m^ , and over the northern
shelf (north of 60° N) 21.8 g/m' (Fig. 57-6).
Cooney (1978) describes seasonality in the bio-
mass of zooplankton collected in the southeast
952 Plankton ecology
- 60° N
- 50° N
ZOOPLANKTON AND MICRONEKTON COMMUNITIES
Oceanic and Outer-Shelf Community
Calanus cristatus
C. plumchrus
Eucalanus bungii bungii
Metridia pacifica
Pseudocalanus spp.
Oithona similis
Parathemisto pacifica
Thysanoessa longipes
T. inermis
Eukrohnia hamata
Sagitta elegans
Middle-Shelf and Coastal Community
Pseudocalanus spp.
Acartia longiremis
Oithona similis
Calanus glacialis
C. marshallae
Parathemisto libellula
Thysanoessa raschii
Sagitta elegans
Nearshore Community
Acartia clausi
Podon sp.
Centropages abdominalis
Eurytemora pacifica
Evadne sp.
Pseudocalanus spp.
E. herdmani
Tortanus discaudatus
Figure 57-5. Large-scale distributions of zooplankton and micronekton communities representative of the eastern Bering
Sea.
Bering Sea in the spring, summer, fall, and late winter
months (Fig. 57-7). These values are used to com-
pute the seasonal variation in carbon (assumed to
be 45 percent of the dry weight: Ikeda and Motoda
1978) in the biologically defined regions on both
sides of the frontal system at 80 to 100 m (Fig.
57-8). The stock of oceanic species is greatest in
May and June and lowest in November. Conversely,
the shelf zooplankton stocks do not reach a maxi-
mum until late summer and are lowest in the spring.
These collections were made in 1975 and 1976, a
period of below-normal temperatures and extreme
sea-ice cover in winter. It is not known how the
presence of sea ice may have affected seasonality in
the animal plankton stocks.
This sequencing of oceanic and shelf stocks is in
general accord with published accounts of the known
life cycles of the dominant species in these two major
hydrographic domains (Vinogradov 1968). As men-
tioned previously, the bulk of the oceanic popula-
tion overwinters at depth. The large calsmoid cope-
pods Calanus cristatus and C. plumchrus reproduce
Zooplankton and micronekton communities 953
170°W
160 E
- 60° N
50° N
Figure 57-6.
1974).
Distribution of wet-weight biomass (g/m'^) of net zooplankton in the Bering Sea (from Motoda and Minoda
in late winter without first having to feed, and their
progeny swarm in the near-surface water before the
onset of the bloom. The immature stages are so
efficient at utilizing the developing plant stocks that
the bloom at some locations takes the form of a
biomass increase at the first-order consumer level
rather than at the primary-producer level (Parsons
1966). This kind of seasonally influenced distribu-
tional pattern as deep as the upper 200 m in the
water over the outer shelf is illustrated by variations
in the abundance of Calanus cristatus (see Appendix
57-11, Fig. 5). This species is common from spring
through late summer but absent in the upper 200 m
in the fall.
In contrast, the shelf species Pseudocalanus spp.,
Acartia longiremis, and Calanus marshallae are most
numerous in the late spring or fall. Both Pseudocal-
anus and Acartia produce several generations, and the
annual brood of C. marshallae appears later in the
summer (see Appendix 57-11, Figs. 4, 7 and 12).
Thus, the shelf community peaks after the oceanic
group at a time when the deep-water copepods
are migrating back to wintering depths.
A somewhat more detailed examination of the
biomass structure along the shelf break in late spring
and eairly summer reveals the presence of a band of
high biomass associated with stocks of Calanus
cristatus, C. plumchrus, Eucalanus bungii bungii,
and Metridia pacifica (Fig. 57-9). These popula-
tions occur in greatest abundance in the vicinity of
the shelf-break frontal system which is maintained
in the surface waters along the outer shelf (Iverson
et al. 1979b). Wet weights approaching 200 g/m^
^^
y^OBGy^'
y ■> ^« ^^
^
/^l 2 5 >V^
M
* /071 /^
/ A
%
/^ /3 92
/ M
^ y^ y^ y^
88 /^ y^
jtm
/'
y^^^y y^
Xy ■>'/
^mi'
y s' y^^^y ^y
X ^
jw
4
May
June\ /''^ >/o.98/^ V
V05X X76/
V^X ' / A
\">y w
Ma,eh-«o..l\/ ^y -
^
%.
:
1
1
Figure 57-7. Seasonal distribution of zooplankton dry
weight (g/m^ ) in the southeast Bering Sea; May 1975-
April 1976.
954 Plankton ecology
3.0
U
O)
2.0
1.0
Oceanic and outer-shelf
Middle-shelf and coastal
JFMAMJJASONDJ
MONTH
Figure 57-8. Seasonal variation in zooplankton carbon
for the soutiieast Bering Sea; May 1975-April 1976.
are frequently encountered in this region. The
presence in 1977, 1978, and 1979 of large copepod
populations at the shelf break demonstrates the con-
sistency of this phenomenon.
A more detailed view of the zooplankton biomass
distribution and seasonal variation can now be pro-
posed for the southeast Bering Sea, including Bristol
Bay and the oceanic waters between the Pribilof
Islands and Unimak Pass (Fig. 57-10). The most
obvious feature is the high-density copepod com-
munity at the shelf break. Although the observa-
tions are not available, oceanographic continuity
suggests that these populations probably also exist
further to the north in regions where the shelf-break
front produces adequate food for the oceanic grazers.
Cooney et al. (in press) note that larval walleye
pollock (Theragra chalcogramma) depend entirely
on pelagic foods (copepod eggs, nauplii, and cope-
podids), and that the rapidly growing juveniles
20-30 mm in length and longer regularly ingest the
largest oceanic copepods. This behavior of pollock,
together with the fact that the foreign fishery for
pollock in the slope and outer-shelf waters is one of
the largest single-species fisheries in the world, indi-
cates the trophic importance of the shelf-break cope-
pods in the eastern Bering Sea. Furthermore, Nasu
(1974) concludes that along the eastern shelf, waters
g xloVm^Q 1-20
MAY 1977
A
.^"^i^
g xlO^/m^ii 1-20
MAY 1978
Figure 57-9. Distribution of zooplankton dry weight
along the shelf break of the southeast Bering Sea; May
1977 and 1978.
between 100 and 200 m deep (the region of the
shelf-break copepods) support the highest stocks
of baleen whales in the Bering Sea.
SECONDARY PRODUCTIVITY
Ikeda and Motoda (1978) present the latest and
most comprehensive summary of information about
zooplankton production presently available for the
Bering Sea. Using pooled data from 15 years of
summer observations and relationships between
respiration and body size (Winberg 1956), they
estimate production in four subregions of the Bering
Sea and the waters south of the Aleutian chain.
Bristol Bay and the continental ridge north to about
60° N are said to support the highest rate of zoo-
plankton growth, averaging 121 mg c/m^ /d. Unfor-
tunately, this study integrates stock values across the
Zooplankton and micronekton communities 955
170°W
- 60°N
- 50° N
SEASONAL RANGE IN BIOMASS
(wet weight g/m^ )
Oceanic community
Shelf-break community
13-37
7-180
Mixed community 7 - 60
Middle-shelf and coastal community 7-12
Figure 57-10. Diagrammatic representation of seasonal and spatial variations in wet-weight biomass in the southeast Bering
Sea.
very different domains over the shelf so that cross-
shelf differences in productivity are not discernible.
Studies recently completed in the southeast Bering
Sea (Appendix 57-III) provide the first detailed
evaluation of the contribution of zooplankton to
secondary production in the oceanic /outer-shelf
and middle-shelf domains. This approach assumes
that the grazing stress is roughly proportional to the
mass of dominant species occurring across the shelf
at any time.
Cross-shelf distributions of the numerically domi-
nant herbivorous and omnivorous copepods were
found to be closely correlated with the shelf fronts
(Figs. 57-11, 57-12). The three oceanic species
Calanus plumchrus, Eucalanus bungii bungii, and
Metridia lucens dominated the mass field which is
more developed on the oceanic side of the 80-m
frontal system at about Station 11. At the same
time, particulates in excess of 2 ppm (1 ppm =
10^ livci^ /ml) occurred landward of the middle front,
whereas over the outer shelf and oceanic area, the
particulates were patchy and less concentrated.
Thirteen direct measurements of ingestion for the
oceanic /outer-shelf and middle-shelf communities
were made using shipboard incubations of unsorted
zooplankton collections and naturally occurring
plant stocks (Table 57-3). The resulting values were
multiplied by the combined cross-shelf dry weight of
the six dominant copepods and nauplii and expressed
as the cross-shelf grazing (Fig. 57-13).
The results of this analysis indicate that from the
middle front landward, the dominant small copepods
are able to ingest no more than about 200 mg C/m^ /d,
of which approximately 60 mg goes to grovrth or
secondary productivity. However, at the shelf break,
the high-density stock of large copepods ingests up
Acartia longiremis
(0
CM
E
0)
\
n
in
E
O
3
^"
z
X
CM
Calanus plumchrus
Eucalanus bungii bungii
2 3 4 5 6
Stations
7 8 9 10 11 12 13 14 1516 17 18 19
PROBES 1979
Particulates: 10-160 Mm diameter
(xlO^^mVmO
Figure 57-11. Cross-shelf distributions of numerically dominant copepods and volumes of particulates.
956
Acartia longiremis
Copepod nauplii and metanauplii
Pseudocalanus spp.
ca T
4^
E
£
\
0)
0)
0)
E
^
O
4^
CM
mmm^^^l^mmmm
Oithona similis
Metridia lucens
Ca/anus plumchrus
Eucalanus bungii bungii
Stations
10 1112 13 14151617 18 19
Figure 57-12.
particulates.
Cross-shelf distributions of the wet weights of the numerically dominant copepods and volumes of
957
i400r
CROSS-SHELF GRAZING
COPEPOD DRY WEIGHT
2 3 4 5 6
Stations
7 8 9 10 111213141516171819
Figure 57-13. Cross-shelf combined dry weight and grazing rates of copepods.
958
Zooplankton and micronekton communities 959
TABLE 57-3
Average grazing rates for zooplankton communities occurring
in tiie oceanic/outer-shelf and middle-shelf domains of the
southeast Bering Sea.
Domain gC/m^ /g of grazer^ Range
Leg III
Oceanic/outer
shelf
Middle shelf
1.272 X 10"^
3.182 X 10"^
0.388-3.332 X 10"^
2.421-3.429 X 10"^
^Grazer dry weight.
to 1,400 mg C/m^ /d, producing about 420 mg C/m^
as daily growth. These estimates show that the daily
ingestion of particulates by the numerically dominant
copepods varies greatly across the shelf. Also, since
the particulates in the water column are consistently
high (> 2 ppm; 8-160 equivalent spherical diameters)
during the production cycle at depths of less than
80-100 m, it would seem odd if alternate pathways
of matter ingestion did not occur in the water column.
Dagg (1979) finds appendiculeirians in great abun-
dance in waters over the middle shelf; these organ-
isms must remove some particulates. English (1979)
also estimates, using acoustic methods, that euphau-
siid stocks approaching 100/m^ are common over
the shelf. Thysanoessa inermis and T. raschii are
commonly found (Appendix 57-11, Figs. 18 and 20).
These euphausiids certainly remove some of the
particulates from the water column daily but prob-
ably not more than 10-15 percent of the amounts
removed by copepods (see Appendix 57-III).
The ingestion estimates, representing conditions
at the peak of the phytoplankton bloom in May and
June, were then used to compute annual rates of
secondary production for the same region (Table
57-4). For comparison with other published values,
a growth period of 150 days was used (see Appen-
dix 57-III for computational details and a discussion
of errors).
The cross-shelf differences are important because
of the functional characteristics of the different
zooplankton communities in the Bering Sea (Iverson
et al. 1979a). The strictly oceanic group outside the
influence of the shelf-break frontal system seems to
produce approximately 13 g C/m^ /yr. This agrees
closely with estimates for the open Gulf of Alaska
harboring the same group of taxa (McAllister 1969).
However, this rate underestimates the production
associated with high-density shelf break copepods, 33
g C/m^ /yr, and the upper range for this group, 64 g
C/m^ /yr, is the highest reported for the Bering Sea.
This observation may help to balance ecosystem
models of this region based on the forage require-
ments of fishes, birds, and mammals. In the past such
models have suggested that higher trophic levels
consume forage species in greater quantity than is
annually produced. What has been overlooked is the
seasonally persistent medium-scale patchiness; when
this phenomenon is taken into account, estimates
of secondary production will be higher in some
locations.
If these estimates reflect cross-shelf processes,
waters of the inner-shelf and coastal communities
must support a relatively impoverished pelagic food
web. Indeed, the notion prevails that landward of
the 80-m middle front the system's secondary pro-
duction is primarily benthic, since the synthesis of
organic matter in the water column appears to
exceed the needs of populations of small pelagic
consumers. This view is consistent with observations
of a rich benthos and food webs which support
commercial populations of demersal fishes and
shellfishes (Haflinger 1980). Moreover, Straty
(1974) reports that juvenile sockeye salmon moving
into Bristol Bay grow little or not at all for a period
of four to six weeks before they reach the outer
region of the bay. Low abundance of food during
the sockeye 's eairly residence is cited as a possible
cause for the lack of growth.
Iverson and Goering (1980) report the amount of
annual production of phytoplankton in the south-
east Bering Sea: the outer-shelf water associated
with the shelf-break front is presumed to produce
about 200 g C/m^ /yr, the middle-shelf domain,
including the middle front, is assigned a value of
400 g C/m^ /yr, and the coastal domain shoreward
of 50 m is thought to produce about 120 g C/m^ /yr.
Together with the estimate of Taniguchi (1972)
that the open Bering Sea produces nearly 90 g C/
m^ /yr, these values allow a crude first-order evalua-
tion of the relative efficiency of the consumers of
plant stocks in these regions. The estimate of
13 g C/m^ as annual oceanic secondary production
results in an efficiency of transfer to grazers of about
14 percent. At the shelf break the efficiency is
approximately the same, 16 percent, while over the
middle shelf (mixed community), it drops to only
2 percent, and in the coastal region it is also low,
about 3 percent.
The vastly different interaction between grazers
in the oceanic and outer shelf regions and those
over the middle and inner shelf domains is evident.
The apparent trophic efficiency of less than 5 percent
speaks to the inefficacy of the middle-domain pelagic
grazing community and assures that a considerable
960 Plankton ecology
TABLE 57-4
Estimates of annual zooplankton production for the Bering Sea, April-August
Region and source
gC/m^/yr^
Bering Sea oceanic community
Respiration relationship (Ikeda and Minoda 1978)
Summer biomass (Ikeda and Minoda 1978)
Primary production X 0.30 (Ikeda and Minoda 1978)
Population dynamics (Heinrich 1962)
Ingestion'^ (Cooney, this chapter)
Shelf-break community
Ingestion (Cooney, this chapter)
Mixed community
Ingestion (Cooney, this chapter)
Inner-shelf and coastal community
Ingestion (Cooney, this chapter)
Population dynamics (Heinrich 1962)
6.0-18.2(13.3)
1.0-4.3 (3.3)
27.0
7.8
16.1-23.3 (19.6)
17.3-64.1 (32.8)
7.1-10.2(7.9)
1.7-5.7(4.0)
0.7
^Assuming a 150-day production period; average value in parentheses.
•^Production = 0.3 ingestion (Winberg 1956).
proportion (perhaps as much as 90 percent) of the
organic matter produced in the water column land-
ward of the middle front is accessible to benthic
detrital feeders. Bakkala et al. (1979), in a review
of groundfish resources of the eastern Bering Sea
and Aleutian Islands, specify regions where Japanese
fishermen catch several important fin-fishes: walleye
pollock. Pacific cod. Pacific ocean perch, sablefish,
and Greenland turbot and arrowtooth flounder are
all caught over the outer shelf and slope. These
species rely heavily on a pelagically supported food
web.
Yellowfin sole and other flounders inhabit the
middle-shelf region, where benthic forage species
contribute heavily to the diet. Thus, the partitioning
of plankton species in the water column is reflected
at higher trophic levels.
ACKNOWLEDGMENTS
I am grateful for the assistance of M. Clarke,
K. Coyle, A. Adams, and P. Wagner, who partici-
pated in the field program at sea, and were primarily
responsible for the taxonomy and sorting of col-
lections in the laboratory.
This work. Contribution No. 427, Institute of
Marine Science, University of Alaska, was supported
by the National Oceanic and Atmospheric Adminis-
tration Outer Continental Shelf Environmental
Assessment Program, contract number 03-5-022-
56, and by the National Science Foundation Grant
DPP 76-23340-A02 (PROBES).
APPENDIX 57-1
Listing of zooplankton and micronekton species collected
in the southeast Bering Sea with 1-m ring nets and 2-m NIO
trawls, May 1975-June 1977.
CNIDARIA
Hydrozoa
Aegina rosea
Aequorea forskalea
Aglantha digitale
Botrynema brucei
BougainvilUa superciliaris
Calycopsis nematophora
Corymorpha flammea
Coryne princeps
C. tubulosa
Crossota brunnea
Eirene indicans
Halicreas minimum
Melicertum campanula
Obelia longissima
Pantachogon haeckeli
Perigonimus breviconis
P. multicirratus
P. yoldia arcticea
Ptychogena lactea
Rathkea jaschnowi
Tubularia prolifer
Scyphozoa
Atolla wyvillei
Aurelia limbata
Chrysaora helvola
C. melanaster
Cyanea capillata
Zooplankton and micronekton communities 961
Periphylla hyacinthina
Phacellophora camtschatica
Siphonophora
Dimophyes arctica
Ramosa vitiazi
Rosacea plicata
Vogtia serrata
CTENOPHORA
Beroe spp.
CHAETOGNATHA
Sagitta elegans
S. c. f. S. maxima
Eukrohnia bathypelagica
E. hamata
ANNELIDA
Antinoella sarsi
Capitella capitata
Chaetozone setosa
Eteone longa
Glycera capitata
Hesperone complanata
Krohnia excellata
Laonice cirrata
Lopadorrhynchus sp.
Lumbrinereis sp.
Maldane sarsi
Nereis pelagica
Pelagobia longicirrata
Scoloplos armiger
Terebellides stroemii
Tomopteris septentrionalis
Typhloscolex muelleri
MOLLUSCA
Berryteuthis magister
Chiroteuthis sp.
Clione limacina
Euclio sp.
Galiteuthis sp.
Gonatus sp.
Gonatopsis sp.
Limacina helicina
ARTHROPODA
Cladocera
Evadne sp.
Podon sp.
Ostracoda
Conchoecia alata minor
C. borealis var. antipoda
C. borealis var. maxima
C. curta
C. pseudoalata
C. pseudodiscophora
C. skogsbergi
Copepoda (Harpacticoida)
Brady a sp.
Ectinosoma sp.
Microsetella rosea
Tisbe sp.
Copepoda (Calanoida)
Acartia longiremis
A. tumida
Aetideus pacificus
Aetideus sp.
Bradyidius saanichi
Calanus cristatus
C. glacialis
C. marshallae
C. plume hrus
Candacia columbiae
Centropages abdominalis
Chiridius gracilis
Eucalanus bungii bungii
Euchaeta elongata
Eurytemora herdmani
E. pacifica
Gaetanus intermedius
Gaidius variabilis
Haloptilus pseudooxycephalus
Heterorhabdus compactus
Heterorhabdus sp.
Lucicutia ovaliformis
Lucicutia sp.
Metridia lucens
M. ochotensis
Microcalanus spp.
Pachyptilus pacificus
Pleuromamma scutullata
Pseudocalanus spp.
Racovitzanus antarcticus
Scolecithricella minor
S. ovata
Spinocalanus sp.
Xanthocalanus kurilensis
Xanthocalanus sp.
Copepoda (Cyclopoida)
Oithona similis
O. spinirostris
Onceae borealis
Nebaliacea
Nebalia sp.
Isopoda
Ilyarachna sp.
Synidotea bicuspida
Mysidacea
Acanthomysis dybowskii
A. nephrophthalma
A. pseudomacropsis
A. stelleri
Boreomysis californica
B. kincaidi
Eucopia sp.
Holmesiella anomala
Neomysis czemiawskii
N. ray a
Pseudomma truncatum
Cumacea
Diastylis alaskensis
D. bidentata
Eudorella pacifica
Eudorellopsis deformis
Lamprops quadriplicata
Leucon fulvus
L. nasica orien talis
Leucon sp.
Amphipoda (Gammaridea)
Ampelisca macrocephala
Anisogammarus macginitiei
Anonyx compactus
A. lilljeborgi
A. nugas pacifica
Argissa hamatipes
Atylus bruggeni
A. collingi
Bathymedon nanseni
B. obtusifrons
Byblis gaimardi
Corophium sp.
Cyclocaris guilelmi
Cyphocaris anonyx
C. challengeri
Dulichia arctica
D. unispina
Dulichia sp.
Eusirella multicalceola
Guernea sp.
Hippomedon kurilicus
Ischyrocerus anguipes
L commensalis
Ischyrocerus sp.
Lepidepecreum comatum
L. kasatka
Melita dentata
Melitoides makarovi
Melphidippa sp.
Metopa alderi
Monoculodes diamesus
M. packardi
M. zernovi
Monoculopsis longicomis
Orchomene lepidula
O. nugax
O. obtusa
Paramphithoe polyacantha polyacantha
Parandania boecki
Paraphoxus sp.
Photis sp.
Pleustes panoplus
Pleusymptes glaber
Pleusymptes sp.
Pontogenia ivanovi
Pontoporeia femorata
Priscillina armata
Protomedia sp.
Rhachotropis natator
R. oculata
Socarnes bidenticulatus
Westwoodilla caecula
962 Plankton ecology
Amphipoda (Hyperiidea)
Archaeoscina steenstrupi
Hyperia galba
H. medusarum
H. spinigera
Hyperoche medusarum
Paraphronima crassipes
Parathemisto japonica
P. libellula
P. pacifica
Phronima sedentaria
Primno macropa
Scina borealis
S. rattrayi
Euphausiacea
Euphausia pacifica
Tessarabrachion oculatus
Thysanoessa inermis
T. longipes
T. raschii
T. spinifera
Decapoda
Argis lar
Cancer sp.
Chionoecetes spp.
Crangon dalli
Erimacrus isenbeckii
Eualus macilenta
E. stonyei
Hymenodora frontalis
Hyas sp.
Pandalopsis spp.
Pandalus borealis
P. goniurus
P. montagui tridens
Paralithodes camtschatica
Pasiphaea pacifica
Sergestes similis
Telmessus cheiragonus
CHORDATA
Larvacea
Fritillaria borealis
Oikopleura spp.
Cyclostomata
Lampetra tridentatus
Teleostei
Agonus acipenserinus
Ammodytes hexapterus
Artediellus pacificus
Atheresthes stomias
Bathylagus alascanus
B. pacificus
Bathymaster signatus
Chaulidos macouni
Clupea harengus pallasi
Hemilepidotus sp.
Hippoglossoides elassodon
Hippoglossus stenolepis
Leuroglossus stilbius schmidti
Liparis dennyi
L. herschelinus
Liparis spp.
Lumpenus maculatus
L. medius
Ly codes palearis
Malacocottus zonurus
Mallotus villosus
Nectoliparis pelagicus
Ptilich thys goodei
Reinhardtius hippoglossoides
Sebastes sp.
Stenobrachius leucopsarus
S. nannochir
Theragra chalcogramma
Triglops pingeli
APPENDIX 57-11
Cross-shelf distributions of 21 zooplankton and micronek-
ton species were sampled in the southeast Bering Sea, May
1975-April 1976. Darkened circles indicate the open-ocean
domain (> 200 m), squares the outer-shelf domain (100-200
m), open circles the middle-shelf region (50-100 m), and
triangles the coastal domain (< 50 m). Confidence intervals
(P = 0.05) are depicted for each species based on an average
of nine observations per mean.
M
F M A
1976
M
A S
1975
Figure 1. Cross-shelf seasonal abundance of Aglantha
digitale in the southeast Bering Sea: May 1975-April 1976.
Figure 2. Cross-shelf seasonal abundance of Clione
limacina in the southeast Bering Sea: May 1975-April 1976.
10'
Figure 3. Cross-shelf seasonal abundance of Limacina
helicina in the southeast Bering Sea: May 1975-April 1976.
10^
0) 10"
E
10
-i_
-L.
J
M J
J A S
1975
O N
F M A M
1976
Figure 4. Cross-shelf seasonal abundance of Acartia
longiremis in the southeast Bering Sea: May 1975-April
1976.
►
MJJ ASONDJFMAM
1975 1976
Figure 5. Cross-shelf seasonal abundance of Calanus
cristatus in the southeast Bering Sea: May 1975-April
1976.
Figure 6. Cross-shelf seasonal abundance of Calanus
glacialis in the southeast Bering Sea: May 1975-April 1976.
963
ioV
10^-
^ 9
JQ
E
10 -
j-
J-
_L
J-
MJJASONDJFMAM
1975 1976
Figure 7. Cross-shelf seasonal abundance of Calanus
marshallae in the southeast Bering Sea: May 1975-April
1976.
Figure 8. Cross-shelf seasonal abundance of Calanus
plumchrus in the southeast Bering Sea: May 1975-April
1976.
Figure 9. Cross-shelf seasonal abundance of Eucalanus
bungii bungii in the southeast Bering Sea: May 1975-
April 1976.
Figure 10. Cross-shelf seasonal abundance of Metridia
pacifica (= lucens) in the southeast Bering Sea: May 1975-
April 1976.
964
10=
10
£t 10
E
10'
U L.
-L
. -I I I I I
MJJ ASONDJ FMAM
1975 1976
Figure 11. Cross-shelf seasonal abundance of Oithona
similis in the southeast Bering Sea: May 1975-April 1976.
Figure 12. Cross-shelf seasonal abundance of Pseudo-
calanus spp. in the southeast Bering Sea: May 1975-April
1976.
10
10'
n 10
3^
10
10'
3^
.o 10
E
J I 1 L
J L
J
MJJ ASONDJFMAM
1975 1976
Figure 13. Cross-shelf seasonal abundance of Eukrohnia Figure 14. Cross-shelf seasonal abundance of Sagitta
hamata in the southeast Bering Sea: May 1975-April 1976. elegans in the southeast Bering Sea: May 1975-April 1976.
965
10"
10'
n 10
E
3
Z
1 -
1975
Figure 15. Cross-shelf seasonal abundance of Parathemisto
libellula in the southeast Bering Sea: May 1975-April
1976.
Figure 16. Cross-shelf seasonal abundance of Parathemisto
pacifica in the southeast Bering Sea: May 1975-April 1976.
1976
Figure 17. Cross-shelf seasonal abundance of Chionoe-
cetes spp. in the southeast Bering Sea: May 1975-April
1976.
Figure 18. Cross-shelf seasonal abundance of Thysanoessa
inermis in the southeast Bering Sea: May 1975-April 1976.
966
Zooplankton and micronekton communities 967
Y
Figure 19. Cross-shelf seasonal abundance of Thysanoessa
longipes in the southeast Bering Sea: May 1975-April
1976.
Figure 20. Cross-shelf seasonal abundance of Thysanoessa
raschii in the southeast Bering Sea: May 1975-April 1976.
Figure 21. Cross-shelf seasonal abundance of Oikopleura
spp. in the southeast Bering Sea: May 1975-April 1976.
APPENDIX 57-III
Secondary production estimates
This discussion is appended in order to point out errors
associated with the direct measures of particle ingestion and
their incorporation into estimates of secondary productivity
and annual production.
The author's estimates of secondary productivity and
annual production are based on a small number of direct
community ingestion measurements conducted during the
spring of 1979 in the southeast Bering Sea.
The method involved shipboard incubations of naturally
occurring plant and animal stocks in large plastic bottles.
Twenty-liter cubitainers were filled with unfiltered seawater,
using the ship's non-toxic system (~ 3 m) or by pumping
water from the upper 30 m. Net caught zooplankton (un-
sorted) collected by vertical tows (0.202 mm Nitex) in the
upper 50 m of the water column were poured into these
containers and the bottles rotated slowly in a bath of running
surface water (3-6 C) to maintain a suspension of particles.
Controls without additions of zooplankton were also incu-
bated. At two- and six -hour intervals, samples were taken to
measure the rate at which suspended particles were removed
by grazers. Subsamples of 50 ml were counted and sized
electronically (Coulter Counter Model TAjj) over the size-
range 8-160 Mm equivalent spherical diameters (ESD). The
experiments were conducted for periods of 25-58 hours, after
which the grazing community was collected and preserved for
later identification, enumeration, and weighing.
Table 1 of this appendix lists the zooplankton which
figured in experiments conducted on Leg III (May/June) of
the PROBES 1979 cruise. Thirty-one taxonomic categories
TABLE 1
Taxonomic constituency of collections recovered from experimental grazing incubations,
May /June 1979, southeastern Bering Sea
Taxonomic category
Oceanic/Outer-Shelf
N0./2OI
Middle-shelf/Coastal
Cnidaria
Hydromedusa early stage
2
100
Obelia longissima
1
Annelida
Polychaeta
1
Mollusca
Gastropod larvae
7
1
Limacina helicina
1
Crustacea
Copepoda
Calanus cristatus
7
10
4
1
C. marshallae
58
75
100
16
22
C. plumchrus*
546
367
355
1
32
28
3
75
Calanus sp.
7
11
10
Eucalanus bungii bungii*
47
93
35
68
74
Microcalanus spp.
7
10
1
Pseudocalanus spp.*
193
153
63
20
88
97
7600
5425
5750
17100
4566
3975
968
Metridia lucens*
213
153
125
2
6
5
Metridia sp.
20
Acartia longiremis*
20
27
15
2
2
200
450
400
2700
967
800
193
A. tumida
27
13
20
1
50
25
Acartia sp.
7
10
1
100
50
100
33
20
Centropages abdominalis
1
25
7
Epilabidocera amphitrites
1
5
Copepod metanauplii*
10
41
46
50
25
25
13
Oithona similis*
20
10
3
69
74
300
250
950
1100
400
425
206
Crustacea
Onceae sp.
7
3
1
Euphausiacea
Thysanoessa inermis
2
11
Euphausiid furcilia
11
1
2
Euphausiid calytopis
1
3
Paguriidae zoea
Barnacle nauplii
1
Chaetognatha
Sagitta elegans
300
24
13
16
Echinodermata
Bipinnaria
7
Echinopluteus
6
6
Ophiopluteus
2
2
Chordata
Scorpaenidae
1
TOTALS
1104
835
665
39
337
341
8275
6450
7256
21400
6010
5265
1432
No. per liter
55
42
33
2
17
17
414
323
363
1070
301
263
72
%*
94
95
92
67
91
94
99
97
98
98
99
99
96
*numerically abundant in the water column
968
appeared in the samples, six numerically dominant copepods
and copepod nauplii were determined; these species comprised
67-99 percent of the animals in the containers. Numbers of
experimental organisms varied over roughly two orders of
magnitude, from 17 to 1,070/1.
The subsequent calculations of ingestion were based on
particle removal rates in the window 10-80 jum EDS. This
was done to avoid machine noise in Channel 1 (8 lum) and to
eliminate the considerable variability in counts when parti-
cles were larger than 80 /um. The range in particle size nearly
always encompassed the volume bloom in the water column
at this time (Appendix 57-III, Fig. 1). Measured differences
in particulate volumes with time were then converted to
carbon ingestion using 0.085 picogram C/)Um^ (an average
of values reported by Mullin et al. 1966), assuming all the
particulates to be phytoplankton (Table 2 of this appendix).
Cross-shelf grazing stress was calculated by applying the
average ingestion rates from the oceanic/outer-shelf and
middle-shelf/coastal regimes to the measured and combined
dry weights of the six numerically dominant copepods and
nauplii across the shelf; Station 13 was considered the first
middle-shelf station (Fig. 57-13).
This simplistic approach assumes proportionality between
the biomass of grazers counted in the water column at any
time and the rate at which suspended particulates are removed;
no attempt was made to differentiate the vertical component
in grazing shown by Longhurst (1976) to be a factor control-
ling the depth distribution of phytoplankton. Moreover, it
is known (Frost 1972) that ingestion rates vary directly with
the availability of plant cells, so that a given mass of grazers
will ingest particles in proportion to their abundance until
a satiation level is reached; the smaller copepods commonly
are sated at lower food densities. This means that simple
incubation experiments which do not account for vertical
stratification of grazers and their food do not closely mimic
the ingestion process in the water column. The present study
suffers from such an inadequacy; the direction and magnitude
of the bias are unknown.
Zooplankton and micronekton communities 969
Ingestion rates were probably underestimated by using
only count data in the window 10-80 /Jm ESD. Although
this range consistently covered the peak volume of partic-
ulates, uptake at the lower end of the spectrum by smaller
copepods would have increased the rate, particularly for the
middle-shelf community. There is continued controversy
in the literature concerning selective grazing by copepods in
the water column. Most recent studies indicate that copepods
are able to shift to particles of whatever size is abundant
(Gamble 1978, Poulet and Chanut 1975). Pseudocalanus
can ingest particles between 4 and 100 fim (Poulet 1974),
although it prefers cells in the 25-57 /im range.
The contribution of daily migrating deep-water zooplank-
ton and micronekton to the grazing was also not evaluated.
The consequent error was not expected to be appreciable
over the shelf where net tows integrated the entire water
column, except for euphausiids, which were probably not
counted accurately with the 1-m net. English (1979) esti-
mates from acoustic records that euphausiid densities
approaching 100/m^ are commonly observed in patches over
the slope and shelf. If these organisms (Thysanoessa inermis,
T. raschii) graze at rates comparable with those of the large
copepods (i.e., ~ 30 mg C/d/g of grazer), and average 10 mg
dry weight each (15-20 mm size-class), ingestion rates of 30
mg C/m /d result. This amounts to approximately 15 percent
of the average middle-shelf and about 6 percent of outer-
shelf/oceanic grazing. Except for local swarms, the contribu-
tion to grazing by euphausiids is small and most important
over the middle-shelf area.
The conversion of plant-cell volume to carbon used here,
0.085 picograms//im^ , is on the high end of a scale from
0.060 to 0.090 for the Bering Sea (Dagg 1979). This value
probably inflates the estimates, but not much.
Finally, crowding has been suspected of causing variation
in rates of ingestion in grazing experiments. Ingestion rates
from the incubations were plotted against both the numbers
and mass of experimental organisms to examine this possi-
bility (Fig. 2 of this appendix). Except for one of the oceanic
TABLE 2
Numbers of organisms, dry weights, changes in particle volume and calculated carbon, duration of experiment
and rates of ingestion for grazing experiments conducted in the oceanic/outer-shelf and middle-shelf domains
of the southeast Bering Sea, May /June 1979.
Community type
NO./201
Wt.,mg Aio6;xm^/ml' Amg C/201
hr
mg C/hr/g of
grazer
Leg III
Oceanic/outer-shelf
Middle-shelf /coastal
1104
414
4.317
7.338
25.0
0.709
835
266
1.518
2.580
25.0
0.380
665
265
1.621
2.756
25.0
0.416
39
102
1.443
2.453
25.0
0.962
337
45
2.800
4.761
58.0
1.824
341
37
4.206
7.150
58.0
3.332
8275
103
5.194
8.830
25.0
3.429
6450
106
5.300
9.010
25.0
3.400
7256
102
4.692
7.976
25.0
3.127
21400
133
3.902
6.633
20.6
2.421
6010
40
3.438
5.844
43.6
3.351
5265
34
2.952
5.018
43.6
3.385
1432
15
1.216
2.066
43.6
3.159
970 Plankton ecology
6.0
E
o
O
5.0
4.0
STA 19
STA 17
STA 4
STA 9
STA 11
STA 7
J \ l__L
I
J \ \ I
10 20 30 40 50 60 70 80 90 100 110
ESD(>im)
Figure 1. Distribution of particle sizes at 10 m for
selected stations along the PROBES transect on Leg III,
1979.
measurements, the observed rates of ingestion exhibited small
differences over wide ranges of grazer concentration and
tended to cluster by regime; rates associated with the middle-
shelf and coastal community were about three times those
measured for the outer-shelf/oceanic regime. The averages
for these two areas based on this small number of observa-
tions are different (P < 0.01).
The error structure of the basic estimates is unknown.
However, since most of the biases discussed are negative for
the method employed, the results reported here are probably
underestimates.
The extension of these averaged values to further estimates
of annual secondary production is based on the assumption
that the cross-shelf portion of grazing described for May/June
is representative of the broader production season. This
contention has not yet been tested in the field. However,
Cooney (1979) reports that the community trend in species
D
A^ A
/
3.0
: A
A
■
A
2.0
0
b
;o
■ O
;@
o
1
1 1 1 1 1 1
■ III
100 200 300 400 500 600 700 800 900 1000 1100
Experimental Animals (No. per liter)
: A
: ^
:A
A
B
■
A
: o
oo
r o
O
\
O
1
@
r
O
1
u
D>
E 10
100 200 300 400
mg dry weight (per 20 liter)
Figure 2. Relationships between ingestion rates and the
number (a) or mass (b) of organisms in experimental
containers (a indicates middle-shelf/coastal assemblage;
o indicates oceanic/outer-shelf group).
and biomass distributions is established early in April; observa-
tions are lacking for the summer and early fall seasons. Given
this constraint, secondary production values were computed
from the cross-shelf grazing structure with a carbon gross-
growth efficiency of 30 percent (Mullin and Brooks 1970)
and a production period of 150 days. Estimates for four
community types were obtained by partitioning the transect
grazing rates into: (1) oceanic (Stations 1-2); (2) shelf break
(Stations 3-6); (3) outer shelf (Stations 7-13); and (4) middle
and coastal (Stations 14-19) and applying the oceanic/outer-
shelf grazing rate to the first three areas and the middle-
shelf and coastal rates to the last six stations on the transect.
In summary, rates of ingestion and secondary production
included by the author must be considered first-order esti-
mates, at best, of unknown bias. They are presented for want
of more precise measures, and because they reflect a cross-
shelf pattern related to the biomass and community structure
of pelagic consumers in the southeast Bering Sea which is
borne out by a more comprehensive data base and supported
by the physical oceanography of the region.
Zooplankton and micronekton communities 971
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1961 Regional distribution of copepods
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1965 The distribution of zooplankton in
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1965 A general description of some factors
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974 Plankton ecology
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i Nutrient Distributions and Dynamics
in the Eastern Bering Sea
Akihiko Hattori
Ocean Research Institute
University of Tokyo
Japan
John J. Goering
Institute of Marine Science
University of Alaska
Fairbanks
b
ABSTRACT
According to the distribution of nutrients over extended
areas of the eastern Bering Sea four water masses can be
distinguished: the deep Bering Sea water, the outer-shelf
water, the mid-shelf water, and the coastal water. This zona-
tion of nutrient distributions is closely related to the presence
of three oceanic fronts defined by means of temperature-
salinity data, and is consistent with existing descriptions of the
physical oceanographic regime.
The surface and subsurface waters of the Bering Sea shelf
and slope are, in general, richer in phosphate than in nitrate
and silicic acid. However, in the bottom layer of the mid-
shelf domain, nitrate is significantly less abundant than would
be expected from N/P uptake by phytoplankton (~15:1),
and ammonium concentrations are very high. Apparently the
regeneration of phosphate and ammonium is occurring at
substantial rates in this water mass, but oxidation of ammo-
nium to nitrate appears to be minimal.
In surface waters of some areas of the Bering Sea shelf and
slope, silicic acid is low compared to phosphate. The extent
of depletion varies from place to place, and there is no general
geographical trend. Limited data suggest that areal differences
in species composition of phytoplankton are responsible for
the observed variations in surface silicic acid content.
NO3/POI" values in the bottom water of the mid-shelf
domain in summer and winter are not substantially different.
The ratios do, however, appear to increase slightly during the
winter. They also probably vary from year to year, since
yearly variation in salinity and temperature has been docu-
mented. The middle oceanic front which separates the mid-
shelf domain from the outer-shelf domain is probably present
the year round, providing the separation needed for the
formation of different water types in the two domains.
INTRODUCTION
Nutrient chemistry provides the fundamental
information for understanding the mode and charac-
teristics of biological productivity in the sea. Al-
though the growth of natural populations of marine
phytoplankton is not always regulated by the supply
of nutrients (Goldman et al. 1979), ambient concen-
trations of nutrients apparently affect the standing
stock of phytoplankton, the ultimate source of
nourishment for all animal life in the sea.
The nutrients in the euphotic layer are extracted
by phytoplankton and replenished by vertical advec-
tion of deep waters rich in nutrients. Nutrients are
also supplied to the euphotic layer through biological
recycling mechanisms (Caperon et al. 1979, Codispoti
and Friederich 1978, Harrison 1978, Hattori and
Wada 1974, Hattori et al. 1980, Ketchum and Corwin
1965, Nelson and Goering 1977, Watt and Hayes
1963). In shallow seas, tidal mixing may significantly
influence the distribution of nutrients (Coachman
and CharneU 1979).
The investigations by Coachman and Chamell
(1979) and Schumacher et al. (1979) disclosed three
distinct oceanographic fronts on the southeast Bering
Sea shelf. These fronts exist at least from spring
975
976 Plankton ecology
through fall. In the southwestern portion of Bristol
Bay, south of the Pribilof Islands, the outer front is
located over the 150-200-m isobath region near the
shelf break, and the middle front over the 100-m
isobath. These fronts extend northwestward along
the bathymetric contours and probably reach Cape
Navarin (Kinder and Coachman 1978). The third,
the inner front, occurs further east over the 40-50-m
isobath. Four oceanic regions, the deep Bering
Sea, the outer-shelf domain, the mid -shelf domain,
and the coastal domain, are distinguished by these
fronts (See Fig. 56-1, this volume), and the existence
of the front-interfront system is confirmed by the
distribution of chlorophyll a and by other parameters
(Iverson et al. 1979).
In this review, we summarize available data on the
distribution of phosphate-phosphorus, silicic acid,
nitrate-nitrogen, nitrite-nitrogen, and ammonium-
nitrogen in the eastern Bering Sea and attempt to
characterize water masses of the respective oceanic
domains according to nutrients. Since the outer-
shelf and mid-shelf domains appear biologically most
productive, these areas are emphasized.
DISTRIBUTION OF PHOSPHATE-PHOSPHORUS,
SILICIC ACID, AND NITRATE-NITROGEN
The data from the 1978 summer cruise of R/V
Hakuho Maru (Hattori 1979) indicate that outer-
shelf water is apparently segregated from both
deep Bering Sea water and mid-shelf water. Tempera-
ture-salinity diagrams as well as nutrient-salinity
diagrams confirm this segregation (Fig. 58-1). Ranges
and averages of salinity, temperature, phosphate,
nitrate, and silicic acid in water columns from 0 to
150 m (0 to the bottom where the bottom is less than
150 m) which are enclosed in separate T-S or nutri-
ent-S envelopes are summarized in Table 58-1. Steep
seasonal thermoclines between 30 and 50 m over
the deep Bering Sea, between 20 and 50 m over the
outer-shelf domain, and between 10 and 50 m over
the mid -shelf domain obstruct the vertical mixing
of water between the upper and lower layers. Near
the bottom of the seasonal thermocline or below it,
nutrient concentrations in the outer -shelf water are
invariably higher than those in the deep Bering Sea
water with the same salinities. Summer nutrient
distributions of 1975 show a trend similar to the
1978 distributions (Hattori 1977).
The surface water in the southeast Bering Sea flows
northwestward parallel to the bathymetric contours
of the continental slope near the shelf break, but its
movement is extremely slow (ca. 1 cm/sec) (Kinder
and Coachman 1978, Coachman and Charnell 1979).
Coachman and Charnell (1979) concluded that
advection of the deep Bering Sea water into the
mid-shelf is not significant, that the distribution of
dissolved materials on the shelf is primarily controlled
by lateral diffusion, and that tidal mixing coefficients
TABLE 58-1
Characteristics of water masses of tiie eastern Bering Sea in summer of 1978^
Deep Bering Sea
Outer-shelf
Mid-shelf
Coastal
Salinity (°/oo)
32.66-33.35
(33.04)
32.45-33.03
(32.68)
31.55-31.91
(31.69)
29.18-31.09
(30.60)
Temperature (°C)
2.85-8.50
(4.86)
2.88-8.60
(4.81)
-0.13-7.80
(3.55)
4.72-11.0
(6.48)
Phosphate (/jg at/1)
0.82-2.57
(1.97)
0.46-2.22
(1.68)
0.11-1.72
(0.94)
0.10-0.29
(0.20)
Nitrate (/ig at/1)
2.5-32.2
(22.9)
0.05-28.4
(18.8)
0.0-8.9
(3.1)
0.0-0.07
(0.02)
Silicic acid {ixg at/1)
11.0-83.7
(54.4)
5.2-69.0
(49.7)
5.6-36.2
(23.7)
3.2-24.4
(13.9)
^Ranges of salinity, temperature, phosphate, nitrate, and silicic acid in 0-150-m water columns (0 to the bottom where the
bottom is less than 150 m) are given. Numerical figures in parentheses refer to averages. Data from the 1978 summer cruise
of R/V Hakuho Maru (Hattori 1979) were used (cf. legend to Fig. 58-1).
Nutrient distributions and dynamics 977
.A
MID-SHE
COASTAL
<30m
O)
3 2
4)
£
O.
It)
o
■c 1
o.
31.0
31.5
B
MID-SHELF
COASTAL
--fOOm
32.0 32.5
Salinity %o
33.0
31.0
31.5
32.0 32.5
Salinity %o
33.0
30
J 20
0)
10 -
OUTE
COASTAL
MID-SHELF
- COASTAL
<30m
31.0
31.5
32.0
Salinity %o
32.5
33.0
31.0
31.5
32.0
Salinity%o
32.5
33.0
Figure 58-1. Temperature-salinity and nutrient-salinity envelopes in the eastern Bering Sea in July 1978 (Hakuho Maru
H-78-3 cruise, Hattori 1979). Individual envelopes enclose all station data in 0- to 150-m w^ater columns (0 to the bottom
where the bottom is less than 150 m) at indicated stations: deep Bering Sea, Stations 6, 8, 31, 33, 34; outer-shelf domain,
Stations 10, 11, 30; mid-shelf domain, 13, 28; coastal domain. Stations 14, 16. Dashed lines refer to T-S and nutrient-S
diagrams at Station 9 (1,650 m) seaward of Zhemchug canyon.
for horizontal eddy diffusivities are similar within
each oceanic front, but an order of magnitude greater
between fronts; the fronts evidently inhibit lateral
fluxes of water and dissolved materials. The nu-
trient zonation shown in Fig. 58-1 is consistent wdth
this physical regime.
In surface layers of the mid-shelf domain shallower
than 20 m, late spring and early summer concentra-
tions of nutrients are commonly low (0.1-0.8 jUg
at/1 of phosphate, 0-3.8 of nitrate, and 4-49 of
silicic acid), and increase sharply with depth, re-
flecting the nutrient consumption associated with
rapid phytoplankton growrth. The bottom layer of
the mid -shelf domain is cold and rich in nutrients,
and probably represents a remnant of the winter
ocean. Data from the mid -shelf domain in winter
(McRoy and Goering 1974) show almost uniform
vertical distributions of temperature, salinity, and
nutrients, not unlike those found in the bottom layer
in summer. In the coastal domain summer nutrient
concentrations are also low (0.06-0.3 iig at/1 of phos-
phate, 0-0.1 of nitrate, and 2-24 of silicic acid), but
do not show any significant vertical trend because
the water is mixed from the surface to the bottom
by wind and tides.
Distinguishing the outer-shelf water from the
deep Bering Sea water is at times difficult. One
example, data obtained at Station 9 (1,650 m deep)
of the 1978 summer cruise of R/V Hakuho Maru,
near the Zhemchug submarine canyon, is shown in
Fig. 58-1. The upper water exhibits the characteris-
tics of the outer-shelf water, the lower water those of
the deep Bering Sea water. A relatively strong
westbound current with a flow of 10 cm /sec has been
reported by Coachman and Charnell (1979) near
Pribilof submarine canyon south of the Pribilof
Islands. A direct current measurement carried out in
July-August 1978 (Kitano and Kawasaki 1979)
978 Plankton ecology
indicated that the water also moves westward or
west -northwestward in the Zhemchug Canyon region
with a flow speed of 5-13 cm /sec. This may explain
why the upper layer at Station 9 was strongly influ-
enced by the outer-shelf water.
Fig. 58-2 presents temperature-salinity and phos-
phate-salinity diagrams based on data obtained on
the 1969 cruise of R/V Oshoro Mam (Faculty of
Fisheries, Hokkaido University 1970) in the Zhem-
chug Canyon area. Salinities (32.36-33.08O/oo
O
o
^^
0)
3
w
0)
Q.
E
0
_
-. ' 's./
%
/%
'S.
'%
ro %, ,*
'°J
f -^
s»
"^ \ y \
/
\
\
\
1
"
> \ X \
/\
\oUTa
R-SHB
tA ■
2
^
\y —
Ss A '
0^
\
^50ni)J/ V 1
3
.\
K / V- — "x
\
/Vsorn \ "
\
\,
f\i
A Y \
4
-
^^OnW
\
\
\/\
X \
y/
^^A'
5
_
MID-SWELH
\
/ \ **
V y^
A \-
\ \
\
a/ \\
/\
B
\ \
i
r^Onj^
s/ \
\/ \
^
\ \
1
jK
Y
\ N
S /
\ //
r \ \
/\ DEEP
\
M
<3Um.
f ^BERING
7
ft
\
1
^
\
31.5
32.0
33.5
3 -
5
0) 2 -
(0
a
(0
o
1 -
31.5 32.0
33.0
33.5
Salinity %o
Figure 58-2. Temperature and salinity and phospiiate-
salinity envelopes in Zhemchug Canyon area of the Bering
Sea in July 1969 (Oshoro Maru cruise 32, Faculty of
Fisheries, Hokkaido University 1970). Individual envelopes
enclose all station data in 0- to 150-m water columns (0 to
the bottom where the bottom is less than 150 m) at indi-
cated stations: deep Bering Sea, Stations 23, 78, 84, 88,
94, 96, 106, 114; outer-shelf domain, Stations 87, 91, 92,
108, 109, 110; mid-shelf domain. Stations 30, 36.
over the outer-shelf domain and 32.70-33.32^/00
over the deep Bering Sea) fall in almost the same
range as those observed during the summer of 1978,
and the two water masses are clearly distinct with
respect to the distribution of phosphate. We there-
fore conclude that the zonation of nutrients is a
general feature of the eastern Bering Sea in summer.
Unfortunately, nitrate and silicic acid data were not
collected in 1969. At several stations between the
outer-shelf domain and the deep Bering Sea some
mixed structures, similar to those observed at Station
9 of the 1978 summer cruise of R/V Hakuho Maru
were also found (Fig. 58-3). Temperature and
salinity cross sections (not reproduced here) clearly
show the intrusion of the shelf water into the deep
Bering Sea or the intrusion of the deep Bering Sea
water into the outer-shelf domain in this transition
area.
The relationship between atoms of nitrate-N and
phosphate-P is approximated by a straight line with
a slope of about 15:1 over extended areas of the
eastern Bering Sea in summer (Fig. 58-4). This
relationship is similar to the global average in other
marine water (Broecker 1974). The line intercepts
the X-axis, indicating that phosphate is in excess of
nitrate by 0.45-0.60 /ig at /I. Below the seasonal
thermocline, nitrate-N /phosphate-P corrected for
176°
59 -
58° -
173
57°N
Figure 58-3. Zonation of the outer-shelf water and deep
Bering Sea water in Zhemchug Canyon area of the Bering
Sea based on phosphate-saUnity and temperature-salinity
data (cf. Fig. 59-2). •: stations where characteristic outer-
shelf water was found; o: stations where characteristic
deep Bering Sea water was found; x: stations where water
mass exhibited transition character between the two
respective water masses.
Nutrient distributions and dynamics 979
40
30
3- 20
o
cd
10 -
JULY 1975
• Deep Bering Sea
A Outer-Shelf Domain
■ Mid-Shelf Domain
40
30 -
ctf
O)
4
(0
20
10
1 2
Phosphate (^g at/I)
0
1 1
JULY 1978
•
/
- •
Deep Bering Sea
••/
/
A
Outer-Shelf Domain
y
■
Mid-Shelf Domain
A Z
/
-
a/«
/A
/ A
/ A
/a
/■■
a/ #■
> / 1 1
-
1 2
3
Phosphate (jig at/I)
Figure 58-4. Relationship between piiosphate and nitrate in 0- to 150-m water columns of the eastern Bering Sea in sum-
mer. •: deep Bering Sea; A: outer-shelf domain; ■: mid-shelf domain. Left: July 1975 (Hakuho Maru KH-75-4 cruise,
Hattori 1977); right: July 1978 (Hakuho Maru KH-78-3 cruise, Hattori 1979).
excess phosphate ranged from 12.2 to 17.3 (average
15.0 ± 1.3) in July 1975 and from 13.9 to 17.0
(average 15.6 ± 0.8) in July 1978 (Table 58-2).
Marked deviations occur in nitrate-N/phosphate-P
of mid-shelf domain bottom water. The ratio cor-
rected for excess phosphate averaged 9.3 ± 3.4
during the summer of 1975 and 5.3 ± 1.3 during the
summer of 1978 (Table 58-2). These low values
may result from differences in regeneration rates of
phosphate and nitrate. Detrital organic matter and
living phytoplankton are transported from the
euphotic layer to the bottom layer by settling.
Inorganic phosphate is regenerated simply through
hydrolysis of organic phosphates. However, the
decomposition of organic nitrogenous compounds
yields ammonium, which must be further oxidized by
nitrifying bacteria to nitrite and then to nitrate. The
latter process is relatively slow, especially at cold
temperatures. Therefore, since the ammonium which
results from the decomposition of organic matter is
oxidized only at a slow rate, it accumulates in these
waters. In fact, unusually high concentrations of
ammonium (5.2 to 6.3 ng at/1) were observed in the
bottom water of the mid-shelf domain during the
summer of 1978 (cf. Fig. 58-5).
The 1978 summer data indicate that values of
nitrate-N/phosphate-P in the euphotic layer of the
outer-shelf and deep Bering Sea domains are some-
what lower than those below the thermocline,
although standard deviations are rather large (Table
58-2). Nitrate and phosphate are normally taken up
by phytoplankton in a ratio of 15:1 when growth is
mainly supported by nitrate. However, ammonium
serves equally well as a nitrogen source for grow^th of
natural phytoplankton populations in the Bering Sea
(McRoy et al. 1972, Saino and Hattori 1977). There-
fore, the true phosphate-to-nitrogen uptake ratio
will be much greater. The low values for corrected
nitrate-N/phosphate-P thus suggest that phosphate is
much more actively regenerated in the euphotic layer
than nitrate.
Winter values for nitrate-N/phosphate-P in the shelf
waters are not substantially different from the sum-
mer ratios in water below the thermocline (Table
58-2). This suggests that even in winter the exchange
of water between the mid-shelf and outer-shelf
980 Plankton ecology
TABLE 58-2
Nitrate-N/phosphate-P in seawater of the eastern Bering Sea^
Areas
Hattori (1979)
17-29 July 1978
b c
Hattori (1977)
9-13 July 1975
b c
C.P. McRoy
(unpub.) C.P.McRoy
31 Jan-12 Feb (unpub.)
1970 5-21 April 1972
Mid-shelf
summer, above thermocline
below thermocline
winter, whole water column
1.26±0.59
3.9 ±0.9
5.3±1.3
0.27±0.20
5.2 ±2.2
9.3±3.4
5.1±1.3
6.4±1.9
Outer-shelf
summer, above thermocline
3.7±3.3
9.4±8.2
4.1±3.1
below thermocline
12.3±0.4
15.7±0.5
10.2±1.5
14.6±1.4
winter, whole water column
Deep Bering Sea
summer, above thermocline
6.8±2.3
12.1±2.8
7.1±0.2
15.1±1.0
below thermocline
12.3±0.7
15.5±0.8
11.2±1.2
15.5±1.0
11.3±1.1
10.1±0.8
^0-150 m water columns (0 to the bottom where the bottom is less than 150 m) were considered.
^Nitrate-N/phosphate-P values by atoms.
*^ Nitrate-N/phosphate-P corrected for excess phosphate by subtracting x-intercept (see Fig. 58-4) values from observed phosphate
values.
domains is substantially restricted. An increasing
trend in nitrate-N/phosphate-P in the mid-shelf
domain is seen in late winter. Hov^ever, the winter
and summer mid-shelf domain data presented in
Table 58-2 were obtained in different years. A
detailed study of the seasonal variation in nutrient
content of the southeast Bering Sea shelf waters
should supply information critical to understanding
the seasonal circulation and mixing of water on this
shelf.
Fig. 58-6 depicts the relationship between phos-
phate and silicic acid in the eastern Bering Sea in
summer. In subsurface waters below the seasonal
thermocline, the relationship between atoms of silicic
acid-Si and phosphate-P is approximated by a straight
line with a slope of 33:1. Phosphate-P exceeds silicic
acid-Si by 0.2-0.5 /.(g at /I, a range similar to the excess
of phosphate-P over nitrate-N. At certain stations, the
linear relationship holds true in shallow layers; at
others, substantial deviations aire noted for water
above the thermocline. The extent of these devia-
tions varies from station to station; a geographical
trend is not evident.
The observed difference in the distribution of
phosphate and silicic acid in the euphotic layer may
arise from differences in species composition of
phytoplankton. Silicic acid is strictly required for
growth of diatoms but not for growth of other
phytoplankton or dinoflagellates. Diatoms, mainly
Chaetoceros spp. and Denticula seminae, accounted
for 60-90 percent of the phytoplankton cells found in
surface water (0-20 m) at summer 1978 R/V Hakuho
Maru stations (11, 32, and 33) where deviations from
the 33:1 ratio of silicic acid-Si to Phosphate-P were
small (Furuya et al. 1979). At stations where signif-
icantly higher ratios were encountered, the number of
dinoflagellates was substantial. At Stations 8, 9, 10,
and 13, dinoflagellates, mainly Gymnodinium spp.
and unidentified unarmored species, accounted for
more than 50 percent of the cell number.
Silicic acid-Si/phosphate-P values lower than 33:1
are found in the bottom water of the mid-shelf
domain (Fig. 58-6). This implies that regeneration of
silicic acid proceeds at slower rates than that of
phosphate in these mid-shelf bottom waters.
DISTRIBUTION OF AMMONIUM AND NITRITE
The early summer distribution of ammonium along
a cross-shelf transect approximately perpendicular
to the shelf break near Zhemchug Canyon is pre-
sented in Fig. 58-5. In the outer-shelf domain and
the deep Bering Sea, there are high concentrations
of ammonium at ~30 m, where the density gradient
is greatest. The depth of the maximum concentration
Nutrient distributions and dynamics 981
Station q
0
— V.
50
E
>-•
I
h-
CL
m
Q
100
150 —
b
200
8 9 10 11
J I I L
13
T
14
_l_
AMMONIUM
(;ig at N/l)
100km
-J
Figure 58-5. Ammonium (/ig at N/l) cross section in the eastern Bering Sea along a transect extending from 56° 59 N-
177°0l'W to 61°00'N-169°00 W (Hakuho Maru KH-78-3 cruise, Hattori 1979).
of ammonium roughly coincides with the depth of
0.5 percent light penetration, and also with the depth
at which concentrations of dissolved oxygen shift
from oversaturation to undersaturation (Fig. 58-7).
The maximum concentration of ammonium thus
occurs near the boundary between the euphotic and
disphotic layers and near the "compensation point"
with respect to primary production. The fact that
ammonium concentrations below the pycnocline are
relatively low suggests that this maximum comes
from pelagic rather than benthic sources. Cross-shelf
ammonium distributions are similar southeast of the
Pribilof Islands (Fig. 58-8). A pelagic food web,
therefore, appeeirs to dominate wide expanses of the
southeast Bering outer-shelf domain. Excretion of
ammonium by zooplankton and other animals is
the most likely source of the ammonium in the outer-
shelf subsurface maximum.
Nutrient data collected by the PROBES program
(Figs. 58-9 and 58-10) suggest that in the outer-
shelf domain southeast of the Pribilof Islands ammo-
nium concentrations are inversely correlated with
nitrate concentrations. Ammonium concentrations
are relatively low in the southern area (Fig. 58-9),
where nitrate concentrations are high. Conversely,
very high concentrations of ammonium are found in
the northern regions, where the largest vertical
gradients in nitrate decline were observed (Fig.
58-10). This inverse relationship is found over ex-
tensive areas of the Bering Sea and the northern
North Pacific in midsummer (Fig. 58-11).
When nitrate concentrations in the surface layer
of the southeast Bering Sea outer-shelf domain are
high, ammonium concentrations in the subsurface
layers are generally low (Fig. 58-11). Nitrate is
probably the basic source of nitrogen for phyto-
plankton growth and also the source of ammonium
through regeneration. Low nitrate concentrations
in the surface waters result from the active utilization
of nitrate by phytoplankton during the spring and
early summer. Phytoplankton and their debris sink,
but they probably remain for an extended period in
the pycnocline, where ammonium is produced as zoo-
plankton graze and bacteria decompose. The oxida-
tion of ammonium to nitrate in the pycnocline is
probably slow. Values of nitrate-N/phosphate-P,
80
70 -
60 -
rf 50[-
I
."2 40
o
<
o
I 30
20 -
10 -
1 1
JULY 1975 "^ ^o
^7
0
Deep Bering Sea ^Zn
Outer-Shelf Domain ^o
A
D
Mid-Shelf Domain /
/• °
mm.
7 ^ □ /
_
D
i* • /
—
/
—
%
• / •
• / •
A / gr
/ •
/
' 1 1
ou
70
-
o
JULY
Deep
1
1978
Berin
i
g Sea
AA /
/
60
-
A
D
Outer-Shelf Domain
Mid-Shelf Domain
y
O
-
<^
A
A
50
_
J
o
_
3
A J
/a
o
<
40
-
D
•
n /o A
-
o
o
30
—
A
•
°i
_
CO
D
/
/
20
-
/
a
-
10
-
D
[ft
/
1
D
a
1
-
1 2
Phosphate (jig at/I)
1 2
Phosphate ()ig at/I)
Figure 58-6. Relationship between phospiiate and silicic acid in 0- to 150-m water columns of the eastern Bering Sea
in summer, o: deep Bering Sea; A: outer-shelf domain; a: mid-shelf domain. Open symbols refer to water masses at or below
the seasonal thermocline, and closed symbols water masses above the seasonal thermocline. Left: July 1975 (Hakuho Mam
KH-75-4 cruise, Hattori 1977); right: July 1978 (Hakuho Mam KH-78-3 cruise, Hattori 1979).
0 I-
50
a
O
100
150
80 90 10
Nitrate (xO.1)
0 110 120%
— I — Tr-
J l_l
L
J
J.
J.
J.
±
J I
Figure 58-7. Vertical profiles of ammonium, nitrate, nitrite, and oxygen in the Bering Sea basin at Station 8 oi Hakuho
Mam KH-78-3 cruise (after Saino et al. 1979).
982
Nutrient distributions and dynamics 983
Station
I
50
£ 100
a.
Q)
Q
\
150 -
200
40 41 42 43 44 45 46 47 48 49 51 52 53 54 55 60 65
AMMONIUM (mq at N/l)
/
\
0
50 km
_i
Figure 58-8. Ammonium (yug at N/l) cross section in outer Bristol Bay south of the Pribilof Islands (PROBES Thomas G.
Thompson cruise 138 leg 3, 29-31 May 1979).
discussed earlier, confirm the slow regeneration of
nitrate in Bering Sea subsurface waters. The steep
pycnocline hinders the vertical diffusion of water and
dissolved materials and slows the sinking of particu-
late matter (Fig. 58-12). The high concentrations of
ammonium in the subsurface layer thus probably
result from a combination of biological and hydro-
graphic processes. In actuality, the ratios of nitrate
plus ammonium to the corrected phosphate in the
ammonium layer are near the expected 15:1. Ratios
obtained on the 1978 R/V Hakuho Maru cruise
ranged from 12.1:1 to 15.5:1 (average 14.5 ± 0.9:1).
The presence of ammonium maxima in subsurface
layers appears to be a common feature of highly
productive boreal seas dominated by pelagic food
webs.
In the mid-shelf domain, no such maximum con-
centration of ammonium is found in the subsurface
layer. Instead, very high concentrations of ammo-
nium exist near the bottom (Fig. 58-5 and 58-8), sug-
gesting a benthic source of ammonium. There
appears to be no relation between this near-bottom
maximum and the subsurface maximum in the outer-
shelf domain. The mid-shelf front between the
mid-shelf and outer-shelf domains extends to the
bottom and effectively prevents the dispersion of
mid-shelf ammonium offshore.
The different patterns of ammonium distributions
in the mid- and outer -shelf domains of the southeast
Bering Sea appear to result from zonal differences in
food webs. A complex combination of biological
and environmental factors influences the occurrence
and productivity of organisms at all trophic levels
of a food web. On the shelf of the southeastern
Bering Sea, the distribution and abundance of herbi-
vores are dramatically influenced by water circulation
and mixing (Iverson et al. 1979). The patterns of
phytoplankton productivity, level of standing crop,
and nutrient regeneration reflect their distribution
and strikingly illustrate the importance of physical
processes in structuring the food webs of this shelf.
The physical system of the southeastern Bering
Sea shelf contains three fronts and two interfront
regions. This system regulates the biological proc-
esses which lead to separate cycles of nutrient regen-
eration for the outer-shelf domain and the mid-shelf
domain: the source of nutrients for the outer-shelf
domain is the deep oceanic water and for the mid-
shelf domain the shelf-bottom water. High nutrient
concentrations occur in surface waters across the
984 Plankton ecology
Station
18 19
40 80 120 160
Distance (km)
Station
18 19
20
21
22
46
40
£ 80
a
03
o
120 -
•
•
•
•
• •
J:
' G
•
•
• •
• G
•
•
•
•
AMMONIUM (;^g at
1 1
N/l)
40 80 120
Distance (km)
160
Figure 58-9. Distribution of nitrate and ammonium
(/ig atoms N/l) in outer Bristol Bay south of the Pribilof
Islands along a southern transect extending from
55° 06.5'N-167°22.8' to 55°52.4'N-165°17.5'W (Acona
cruise 242, 13-26 May 1977).
shelf during winter. With the onset of spring surface
heating, the water column stabilizes, the spring bloom
commences, and nutrients are consumed. The more
intense spring and summer storms influence total
seasonal productivity by mixing the water column
to sufficient depths so that new nutrients are supplied
to the euphotic zone (Fig. 58-13). By the end of
summer, however, nutrient depletion is a common
feature of the euphotic zone in all shelf domains.
The role of the oceanic fronts in transporting nutri-
ents from deep water to the Bering shelf euphotic
zone is not clear. However, various studies of fronts
on other shelves have demonstrated that they are
important sites of vertical transport of nutrients into
the euphotic zone (Pingree et al. 1977, Fournier et al.
1977), and this is probably also true of the Bering Sea
shelf fronts.
There appear to be two distinct copepod communi-
ties on the southeastern Bering Sea shelf (Cooney
1978, Iverson et al. 1979). A shelf group consisting
of a small standing stock of small animals such as
Pseudocalanus spp. and Acartia spp. is confined to
the region shoreward of the middle front. An oceanic
group consisting of a large standing stock of euphau-
siids and large calanoid copepods is confined to the
outer-shelf domain because of hydrographic condi-
tions which do not allow extensive exchange of
outer-shelf water with mid-shelf water. These two
communities produce an across-shelf differential
grazing stress which significantly influences the
degree of interaction between phytoplankton and
herbivores. The oceanic grazers which are confined
to the outer-shelf domain effectively graze the
diatoms which normally dominate the shelf phyto-
plankton. Their grazing activity results in smaU
standing stocks of phytoplankton (Fig. 58-14),
supplies regenerated nutrients, and slows the onset of
nutrient limitation in the outer-shelf domain. As we
said before, the subsurface maximum concentration
of ammonium in the outer-shelf domain probably
results from this grazing activity. In the mid-shelf
domain the smaller zooplankton are unable to effec-
tively graze large diatoms, which thus flourish and
produce large standing stocks with large nutrient
demands. Much of the phytoplankton biomass in
the mid-shelf domain is not consumed in the water
column but sinks to the sea bed, where it supports a
rich benthic food web and a benthic nutrient regen-
eration cycle. The presence of large concentrations
of near-bottom chlorophyll a and ammonium in the
mid-shelf domain supports this hypothesis (Figs.
58-5, 58-8, and 58-14).
The cross-shelf distribution of nitrite is similar to
that of ammonium (Figs. 58-15 and 58-16), except
Nutrient distributions and dynamics 985
Station
59 16 60 61
Station
59 16 60
40 80
Distance (km)
40 80
Distance (km)
120
Figure 58-10. Distribution of nitrate and ammonium (idg atoms N/1) in outer Bristol Bay south of the Pribilof Islands
along a northern transect extending from 55°26.0'N-168°10.1'W to 56°15.4'N-167°13.0'W (Acona cruise 242, 13-28 May
1977).
8
1
1
1
1
1
7
_
Open symbol:
Shelf Stat
on
.
(
6
h
•
Closed symbol:
+ July
Deep Stat
1971
on
-
4<
i
D
•
• •
O July
D July
1975
1978
-
3(
2l
5
1
1
1
J
■
■
•
•
1
•
+ •
■
1
•
■
1
•
1
10
NO,-
15
20
25
(ng at N/l)
Figure 58-11. Relationship between nitrate concentrations
in the surface layer and ammonium concentrations in the
sub-surface layer in the Bering Sea and the northern North
Pacific (after Saino et al. 1979). Data sources: Hattori
1973, 1977, 1979. +: July 1971; o: July 1975; d: July
1978. Open symbols refer to shelf stations and closed
symbols deep stations.
that the nitrite maximum, like ammonium in the
outer-shelf domain and the deep Bering Sea, is
near the bottom rather than near the top of the
seasonal thermocline (Fig. 58-12). Ubiquitous
occurrences in the open ocean of the subsurface
nitrite maximum and its close association with
chlorophyll maxima are known. However, concen-
trations of nitrite in its maximum layer in the Bering
Sea are several times higher than those observed in
the tropical and subtropical North Pacific (Hattori
1973, 1975; Kiefer et al. 1976).
Two sources of subsurface nitrite have been con-
sidered: production of nitrite during nitrate reduc-
tion by phyto plankton, and production during
ammonium oxidation by nitrifying bacteria (Carlucci
et al. 1970, Miyazaki et al. 1973, Kiefer et al. 1976).
Experiments conducted using '^N-labeled nitrate
and ammonium in the northwestern North Pacific
suggest that the former is mainly responsible for
nitrite production in boreal seas (Miyazaki et al.
1975). Unfortunately, the experimental evidence
986 Plankton ecology
needed to assess which is more important in the
eastern Bering Sea is still lacking.
In the mid-shelf domain, a nitrite maximum is
not evident in the sub-surface layer. Instead, rela-
tively high concentrations of nitrite are found near
the bottom, coinciding with the maximum concen-
tration of ammonium. This nitrite probably is a
product of nitrifying bacteria. However, there are
living plants near the sea bed in the mid-shelf domain
(Fig. 58-14), and these may possibly reduce nitrate
to nitrite. The large concentrations of oxygen in
these waters probably inhibit the reduction of nitrate
to nitrite by bacteria.
In the coastal domain both ammonium and nitrite
concentrations are uniformly low throughout the
water column. In this area the water is shallow
enough for wind and tidal mixing to overlap, and the
result is a thoroughly mixed water column.
HORIZONTAL DISTRIBUTION OF NITRATE
AND AMMONIUM IN SURFACE WATERS OF
THE UNIMAK PASS REGION
Alaskan Stream water enters into the Bering Sea
through Unimak and other Aleutian passes and
bathes the continental slope of the southeastern
corner of the Bering Sea basin (Coachman and
Charnell 1979). Detailed information about nutrient
distributions in the Unimak Pass region can be of
use in identifying the role played by Alaskan Stream
water in the fertility of the southeast Bering Sea.
In Fig. 58-17 the simultaneous measurements
of temperature, salinity, nitrate, ammonium, and
chlorophyll a are presented for a R/V Hakuho Maru
cruise tract (Fig. 58-18) extending about 125 km
southwest of Unimak Pass (Koike et al. 1979).
During the transect the ship moved southeastward
approximately parallel to the bathymetry at a con-
stant speed of ca. 11 kn. Therefore, the tidal current
(~1 kn) effects can be disregarded.
Near the Aleutian Islands, nitrate concentrations
were high (>10 iig atoms N/1) and chlorophyll a
concentrations were relatively low. A decrease in
nitrate westward of Unimak Pass was accompanied by
an increase in chlorophyll a. Highest concentrations
of chlorophyll a were observed at Location B, 17 km
north -north west of Akun Island (Fig. 58-18), where
nitrate concentrations were minimal. These observa-
tions probably reflect the growth of phytoplankton
during the flow of Alaskan Stream water into the
Bering Sea.
Although ammonium concentrations exhibited a
complex pattern, they also tended to decrease west-
ward of Unimak Pass. A small increase in ammonium
accompanied the high concentrations of chlorophyll
a at Location B.
According to Coachman and Charnell (1979),
flow speeds in the Unimak region of the Bering Sea
are 5-10 cm/sec. If a conservative value of 5 cm/sec
is assumed, the Alaskan Stream source water wiU
travel the 40 km from Unimak Pass (Location C)
to Location B, off Akun Island, in about 230 hours.
Salinity and temperature between these two locations
are essentially unaltered, but nitrate concentrations
decrease from 15 ^g atoms N/1 to about 1 /ig atoms
N/1 (Fig. 58-17). Nitrate regeneration in the surface
water during its passage from Location C to Location
B is probably negligible, and nitrate uptake by sur-
,r
E
"- 30
— 1
ug at/I
_33.5%o
_10°C
Temperature
Nitrate (xO.1)
2 ^g ATP/I
^J 6
ppm &
-] pg chl a/I
T
Particle volume (xlO)
Figure 58-12. Vertical profiles of temperature, ammonium, nitrate, nitrite, phosphate, chlorophyll a, ATP, and total particu-
late volume (<64 jum) at Station 8 oi Hakuho Maru KH-78-3 cruise (after Saino et al. 1979).
Nutrient distributions and dynamics 987
0 2
r7
10
50 -
a
(D
O
0 4
NITRATE (>ig at/I)
4 6 8 10 12 14
"I 1 1 1 1 r
Before storm
J I I I 1^^ I
SILICATE (mo at/I)
8 12 16 20 24 28
-i 1 1 1 r
Before storm _
J I I I I ii_:_±
PHOSPHATE (;ig at/I)
0.3 0.6 0.9 1.2 1.5
0
/
' \ '
1 1
10
—
<
/
—
20
—
♦
^~~S^
Before storm _
30
-
x^^ —
After storm
<. .
40
-
A
n
^
50
W
W ^066
— • 2075
1 1 1
1 1
Figure 58-13. Vertical profiles of nitrate, silicic acid and
phosphate before (o) and after (•) a storm for 13-16 May
1979 (PROBES Thomas G. Thompson cruise 138, 79 leg
2).
face phyto plankton is, therefore, estimated to be
~60 ng atoms N/l/h. This value falls in the range
of reported nitrate uptake rates by natural popula-
tions of phytoplankton in outer Bristol Bay (J. J.
Goering, unpublished).
SUMMARY: FUTURE RESEARCH
The distribution of nutrients over extended areas
of the eastern Bering Sea distinguishes four water
masses: the deep Bering Sea water, the outer-shelf
water, the mid-shelf water, and the coastal water.
This zonation of nutrient distributions is closely
related to the presence of three oceanic fronts de-
fined by temperature-salinity data and is consistent
with existing descriptions of the physical oceano-
graphic regime.
Current PROBES investigations are concentrated
in outer Bristol Bay south of the Pribilof Islands,
because this area is biologicadly productive and is
the site of extensive commercial fishing and proposed
oil exploration. Data presented in this chapter and
data from the PROBES program provide a general
description of nutrient cycling in the four different
water types found in the southeast Bering shelf.
Different patterns of nutrient cycling in the various
shelf domains appear to result from zonal differences
in food webs. Nutrient data summarized in this
chapter also suggest that the productive region of
the southeast Bering Sea shelf extends northwestward
along the bathymetry at least to Zhemchug Canyon.
An extensive survey of the hydrography, nutrient
distributions, and productivity of the Bering shelf
northwest of the PROBES study area should provide
important additional information relative to the
seasonal biological productivity of the southeast
Bering Sea and the processes that regulate it.
The surface and subsurface waters of the Bering
Sea shelf and slope are, in general, richer in phosphate
than in nitrate and silicic acid. However, in the
bottom layer of the mid-shelf domain, nitrate is
significantly less abundant than expected from N/P
uptake by phytoplankton (~15:1), and ammonium
concentrations are very high. Apparently the regen-
eration of phosphate and ammonium is occurring at
substantial rates in this water mass, but oxidation of
ammonium to nitrate appears to be minimal. Similar
but less extreme anomalies in the distribution of
nitrate, as exhibited by departure from expected
values of nitrate-N/phosphate-P, are found in the
surface water of the outer-shelf domain and the deep
Bering Sea. These anomalies also probably result from
depressed rates of ammonium oxidation. However,
there is no direct experimental evidence of low rates
988 Plankton ecology
Station
50
100
Q.
<a
Q
150
200
Chlorophyll a (mg/m )
0
L
50 km
_l
Figure 58-14. Chlorophyll a (mg/m^) cross section in outer Bristol Bay south of the Pribilof Islands (PROBES Thomas
G. Thompson cruise 138 leg 3, 29-31 May 1979).
of ammonium oxidation in these waters. The simul-
taneous use of *^N and ^^P to measure ammonium
production, ammonium oxidation, and phosphate
release rates should provide the information need-
14
150
200
; Nitrite (^g at N/l)
0 100km
1 I
Figure 58-15. Nitrite (/ig atoms N/l) cross section in the
eastern Bering Sea along a transect extending from 56°
59'N-177°01'W to 61°00'N-169°00'W (Hakuho Maru
KH-78-3 cruise, Hattori 1979).
ed to test the depressed ammonium oxidation
hypothesis.
In surface waters of some areas of the Bering Sea
shelf and slope, concentrations of silicic acid are low
compared to phosphate. The extent of depletion
varies from place to place, and there is no general
geographical trend. Limited data suggest that local
differences in species composition of phytoplankton
are responsible for the observed variations in surface
silicic acid content. Additional work toward deter-
mining phytoplankton and zooplankton species
composition and the distribution of nutrients in the
southeast Bering Sea should provide the information
needed to test this hypothesis.
Values of nitrate-N/phosphate-P in the bottom
water of the mid-shelf domain in summer are not
substantially different from those in winter. The
ratios do, however, appear to increase slightly during
the winter. They also probably vary from year to year
since yearly variation in salinity and temperature has
been documented. The middle oceanic front which
separates the mid- and outer-shelf domains is prob-
ably present the year round, providing the separation
needed for the formation of different water types in
Nutrient distributions and dynamics 989
180
200
NITRITE
(jLig at N/l)
100
200
Kilometers
300
400
Figure 58-16. Nitrite (jUg atoms N/l) cross section in outer Bristol Bay south of the Pribilof Islands (Thomas G. Thompson
cruise 138, 29-31 May 1979).
the two domains. Continued efforts to collect de-
tailed information concerning the annual variation of
southeast Bering Sea shelf physical, chemical, and
biological variables should be encouraged. Monthly
observations spanning at least one year at selected
representative sites on the shelf of the southeastern
Bering Sea undoubtedly will be needed if annual
variations in these variables are to be identified.
ACKNOWLEDGMENT
Much of the nutrient research described in this
chapter (Contribution No. 428, Institute of Marine
Science, University of Alaska, Fairbanks) was conduc-
ted by personnel of the PROBES program, which
is funded by the National Science Foundation,
Division of Polar Programs, under grant DPP
7623340 to the University of Alaska.
990 Plankton ecology
Figure 58-17. Horizontal variations of nitrate, ammonium, ciiloropliyll a, temperature, and salinity in thie surface waters of
Unimak Pass area on 30 July 1978 (after Koii<e et al. 1979). For locations, see Figure 58-18.
166
164 W
Figure 58-18. Map of Unimak Pass area where data repro-
duced in Fig. 58-17 were obtained.
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Caperon, J., D. Shell, J. Hirota, and E. Laws
1979 Ammonium excretion rates in
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Carlucci, A. F., E. O. Hartwig, and P. M. Bowes
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1978 Local and mesoscale influences on
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1978
Environmental assessment of the
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Nutrient distributions and dynamics 991
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1978 Experimental measurements of nitro-
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1974 Assimilation and oxidation-reduction
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1979 Ecological significance of fronts in the
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1965 The cycle of phosphorus in a plank-
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1976 Another look at the nitrite and
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1978 The front overlying the continental
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1975 The Bering slope current system.
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1979 Current system on the continental
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1978 summer. Proc. 1979 Spring
Meeting Oceanogr. Soc. Japan, 36-7.
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D. Boisseau
1980 Uptake and regeneration of nitrogen
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the effects of copper on these proc-
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Koike, I., K. Furuya, and A. Hattori
1979 Continuous measurements of nitro-
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992 Plankton ecology
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1974 The influence of ice on the primary
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1977 Near-surface silica dissolution in the
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1977 Survival of dinoflagellate blooms in
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1972
J. J. Goering, and W. E. Shiels
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Miyazaki, T., E. Wada, and A. Hattori
1973 Capacities of shallow waters of
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Saino, T., and A. Hattori
1977 Estimate of the growth rate of phyto-
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1979 Ammonium maximum in the Bering
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Schumacher, J. D., T. H. Kinder, D. J. Pashinski,
and R. L. Chamell
1979 A structural front over the conti-
nental shelf of the eastern Bering sea.
J. Phys. Oceanogr. 9:79-87.
1975 Nitrite production from ammonia and
nitrate in the euphotic layer of the
western North Pacific Ocean. Mar.
Sci. Comm. 1:381-94.
Watt, W. D., and F. R. Hayes
1963 Tracer study of the phosphorus
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8:276-85.
Distribution of Walleye Pollock Kggs
in the Uppermost Layer
of the Southeastern Bering Sea
Tsuneo Nishiyama and Tsutomu Haryu'
Institute of Marine Science
University of Alaska
Fairbanks
'Now at Faculty of Fisheries, Hokkaido University
ABSTRACT
Distribution patterns of walleye pollock, Theragra chalco-
gramma, eggs in the uppermost surface layer (0.25 cm) in the
southeast Bering Sea were studied. These studies were based
on data obtained during the 10-29 April 1978 cruise of the
R/V Thomas G. Thompson. One hundred and forty-five
neuston net hauls were carried out over the continental shelf
and slope at depths between 60 and 2,000 m. Water tempera-
tures of the shelf and slope regions were 1.7-4.5 C in the
surface layer and 1.3-4.3 C in the bottom or 200-m layers.
The eggs were widely distributed and were most abundant over
the 60-1 00-m shelf. Very few were found southwest of the
shelf and slope near Unimak Pass. Stage-II eggs (estimated
age: 1-3 days at 3 C) showed the widest distribution, followed
by Stage-Ill eggs (4-7 days old). Stage-VI eggs (19-20 days
old) showed the narrowest distribution. The abundant area of
egg distribution coincided with the 2.5-3 C bottom isotherm
near a sharp temperature gradient along the 100-m isobath. It
has been concluded that this season's spawning took place in
the northern area over the shallow shelf due to the warm
condition of the water. The highest abundance of eggs was
436/10 m^ . The combined mean relative abundance of eggs
of the six developmental stages was 26/10 m^ . Eggs in
stages II and III comprised 85 percent, in stages I and IV 4-6
percent, and in stages V and VI less than 2 percent of the total
abundance. Egg diameters ranged from 1.325 to 1.925 mm.
The mean egg diameter varied from 1.693 to 1.764 mm,
depending upon developmental stage, season, and geographic
location. No difference was found in the mean egg diameter
among the six developmental stages except in stage-Ill eggs in
mid-April. A considerable difference was observed between
eggs in stages I and II and those in stages IV, V, and VI in late
April. Egg diameters were smaller in the young eggs of the
southeast area than in the old eggs of the northern area.
INTRODUCTION
Walleye pollock, Theragra chalcogramma, is the
most significant representative of the family Gadidae
in the southeast Bering Sea. From early spring
through early summer, the eggs and larvae of this fish
constitute a major component of the ichthyoplank-
ton community in this area. Waldron and Vinter
(1978) showed that the ichthyoplanktonic forms of
walleye pollock accounted for 97 percent of the total
fish eggs and 96 percent of the total fish larvae.
Walleye pollock is important not only as a target
species for commercial fisheries but also as a key
organism in the energy transfer of the southeast
Bering Sea ecosystem, for this fish sustains many
marine mammals, sea birds, and demersal fish at
higher trophic levels. The extent of pollock distribu-
tion and its fluctuation greatly influence the spatial
relationships of higher trophic animals as well as the
location of fishing grounds. Therefore, it is essential
to investigate peculiarities of temporal and spatial
distribution of eggs, since the egg distribution pattern
is believed to determine the distribution pattern of
subsequent larval and adult forms.
Surveys of egg distribution in the spawning
grounds have been made in various areas of the
northern North Pacific (Gorbunova 1954, Ito et al.
1955, Ogata 1956, Takeuchi 1972, Dunn and Naplin
1974, Mattson and Wing 1978, Bezludny 1979).
Serobaba (1968, 1975), Maeda and Hirakawa (1977),
and Waldron and Vinter (1978) have discussed
egg distribution, the spawning season, and the spawn-
ing ground in the southeast Bering Sea.
Vertical distribution of eggs has been reported by
Kamba (1977) and Kanamaru et al. (1979).
Gorbunova (1954) and Yusa (1954a) have made
intensive studies of the development and morpho-
logical characteristics of the eggs. Hamai et al. (1971)
examined the effect of water temperature on the
incubation period and mortality of eggs. Fukuchi
(1976) analyzed chemical compositions and oxygen
consumption rates of eggs. This chapter delineates
993
994 Plankton ecology
the distribution pattern of walleye pollock eggs and
describes seasonal and geographical differences in egg
size in the southeast Bering Sea.
MATERIALS AND METHODS
Study area and season
Walleye pollock eggs were collected from 10 to
29 April 1978 during the southeast Bering Sea cruise
of the RV Thomas G. Thompson. The study area was
approximately 370 X 370 km between the latitudes
of 54°30'N and 57°20'N and between the longitudes
of 169°30'W and 163°40'W over depths of 60-2,000
m (Fig. 59-1).
Figure 59.1. Location of neuston and oceanographic
sampling stations occupied in the soutiieast Bering Sea,
April 10-29, 1978. The upper figure shows the stations in
Phase 1, April 10-20, and the lower in Phase 2, April 21-29.
A total of 145 neuston net hauls were carried out
at 157 hydrographic stations. Stations were selected
over almost the entire area of the continental shelf
and slope and partly over the deep sea along transects
across the area from southwest to northeast. Spacing
of two consecutive stations was approximately 6-28
km. The shelf deeper than 100 m is designated as
outer shelf, and the shelf shallower than 100 m as
inner shelf.
Duplicate occupations of the same, or nearly the
same, positions were made after 5-10 days to record
the changes in hydrographic conditions and distribu-
tional patterns and abundance of the eggs. Thus, the
sampling season was divided into two phases: the
first was 10-20 April and the second 21-29 April. A
total of 64 stations were occupied in Phase 1, and
93 stations in Phase 2.
Water temperature and salinity were measured at
hydrographic stations. For geographic comparison of
hydrographic conditions, the study area was tenta-
tively subdivided into four areas: north, northwest,
southeast, and southwest. The extent of each area
varied in the two phases. For each area, mean tem-
perature and salinity values were computed for the
surface, 30-m, and bottom layers. At stations where
the depth was more than 200 m, the value at a
depth of 200 m was used as the bottom layer.
Sampling gear
Egg collection was made with a neuston net called
"Hopping Boy" (Komaki and Morioka 1975). The
structure of this net resembled that of a single-unit
net invented by Zaitsev (1964): it consisted of a
wooden frame with two stabilizing bars and a net.
The frame was rectangular, 0.6 m wide and 0.3 m
high at the mouth. The side stabilizing bars were
0.95 m long. The filtering part of the net was 2 m
long with a 0.35-mm mesh aperture. A hne was
attached to the frame and played out so that the net
was stably submerged at a depth of 0.25 m. The net
was towed at the starboard side of the ship, usually
at a speed of 2 kn for 5-10 minutes. A flowmeter was
not used to determine the volume of water filtered.
Since it was impossible to avoid the effect of bow
waves from the ship, these effects were not taken into
consideration in this study.
The sampling was cancelled in rough sea conditions
when wind force exceeded Beaufort Scale 8. Thirty-
two percent of the stations were occupied at Beaufort
Scale 0-2, 38 percent at 3 and 4, 27 percent at 5 and
6, and 3 percent at 7.
Egg processing and staging
Walleye pollock eggs were preserved in 5-percent
buffered sea water formaldehyde solution, and then
Distribution of walleye pollock eggs 995
k
counted. Developmental stages of the eggs were
determined, and the diameters of thirty eggs for each
station were measured.
The developmental stage of each egg was identified
by referring to Yusa's definition (1954a). Although
Yusa identified 25 developmental stages from ferti-
lized to hatched, we classified the eggs into six
stages in this study, and each egg stage was assigned a
number from I to VI for reference. The notable
morphological characteristics of each egg stage and
the age (the time necessary to reach each stage) at
different temperatures can be summarized as follows:
Stage-I eggs included the newly fertilized eggs,
2-cell, 4-cell, 8-cell, 16-cell, 32-cell, and
morula stage. The eggs of this stage were
less than 13 hours old at 6.6 C (Yusa 1954a)
and one day old at 3 C (Fukuchi 1976).
Stage-II denoted the eggs of blastula, first gastrula,
and early embryo appearance. The embry-
onic shield was differentiated. This stage
was accomplished after one or two days at
6.6 C (Yusa 1954a) and three days at 3 C
(Fukuchi 1976).
Stage-Ill eggs exhibited closure of blastopore and
formation of lenses. The auditory capsules
contained two otoliths. Kupffer's vesicle was
observed. The embryo had 9-16 somites. The
eggs of this stage were four to five days old at
6.6 C (Yusa 1954a) and seven days old
at 3 C (Fukuchi 1976).
Stage-IV eggs were marked by embryos accounting
for almost two-thirds of the outer appearance.
Black pigments were spsirsely distributed over
the dorso-lateral and ventral surface of the
embryo. These eggs were 8 days and 12 hours
old at 6.6 C (Yusa 1954a) and 17 days old at
2C (Hamaietal. 1971).
Stage-V eggs included those in which the embryo
encircled almost three-fourths of the egg
surface. The Kupffer's vesicle disappeared.
The black pigments were distributed over the
embryo. The embryo had almost 40 somites.
The eggs of this stage were 19 days and
12 hours old at 6.6 C (Yusa 1954a) or 18
days at 3 C (Nishiyama in preparation).
Stage-VI eggs had fully encircled embryo and were
ready to hatch. The black pigments appeared
in the eyes and the embryo exhibited a
mouth. The eggs of this stage were about
12 days old at 6.6 C (Yusa 1954a) and
20 days old at 3 C (Fukuchi 1976).
Each egg diameter was precisely measured to
0.001 mm under a binocular microscope. The mean
egg diameter was computed for each developmental
stage and compared between the two phases and
among the four geographic areas. For statistical
treatment, normal curve statistics (Z-value) were used
to compare differences between all pairs of means.
Standardization of abundance
Egg abundance was standardized by dividing the
number of eggs caught by the area sampled (length
of tow X width of neuston net); values are given
in number of individuals per 10 m^ of sea surface.
The abundance was represented in the five ranges of
logarithmic order. Maps of the quantitative distribu-
tion of eggs for each developmental stage were thus
compiled. The mean relative abundance of eggs was
calculated for the two phases. The numerical values
were obtained by dividing the total number of eggs of
respective developmental stages by the entire towing
area.
RESULTS
Hydrographic conditions of study area
Before dealing with temperature regimes and
temperature and salinity characteristics, we summa-
rized the outline of the water system of the study
area. The water system of the Bering Sea and adja-
cent areas has been reviewed by Dodimead et al.
(1963), Takenouti and Ohtani (1974), and Favorite
et al. (1976). Intensive studies have detailed water
masses, fronts, flow patterns, tidal currents, and other
hydrographic characteristics of the southeast Bering
Sea (Koto and Maeda 1965, Ohtani 1969, Kinder et
al. 1975, Coachman and Charnell 1977, Kinder and
Coachman 1978, Coachman and Charnell 1979, Schu-
macher et al. 1979). According to these studies, the
area includes several water masses and fronts.
Oceanic water is characterized by high salinity and
high temperature over the shelf break along the
continental slope; water lower in salinity and temper-
ature overlies the shallow shelf. The southeast
area of the Bering Sea near Unimak Pass and the
Alaska Peninsula is under the influence of coastal
water. The oceanic front is formed along the 150-
200-m isobath, extending from the southeastern
corner of the Bering Sea basin near Unimak Pass to
the south of St. George Island. The middle-shelf
front is found along the 100-m isobath from north of
Unimak Island to the east of St. George Island. The
area encompassed by these two fronts is termed the
outer-shelf zone, and the shelf shallower than 100 m
belongs to the middle-shelf zone. The coastal front
parallels the 50-m isobath along the Alaska Peninsula.
A sluggish flow over the outer shelf and shelf break
extends from southeast to northwest along the
996 Plankton ecology
bottom contour with an average net flow of 1 cm /sec;
the effect of flow upon the transport or dispersion of
eggs in the study area can hence be ignored. On the
other hand, tidal current is known to play an impor-
tant role in energy exchange between oceanic water
and shelf water on a scale of 5 cm /sec; the effect of
this flow on egg distribution, however, has not been
assessed. A discussion of the physical oceanography
of the eastern shelf region is given in Section I,
Volume 1 of this book.
The bottom and surface temperature regimes are
considered to be most important for walleye pollock,
since the former plays a role in determining the
extent of distribution of the spawning population and
the latter regulates directly the developmental proc-
esses of the eggs laid. The distributions of surface
and bottom isotherms in the study area indicated an
increase of temperature from northeast to southwest
or from the shallow shelf to the slope, parallel with
the bathymetric contours (Fig 59-2). In the surface
layer, the 2.5- and 3.5-C isotherms coincided with
the 100- and 200-m isobaths in Phase 1, and the 3-C
and 4-C isotherms with the 100- and 200-m isobaths
in Phase 2. This relation, however, was obscure north
of Unimak Island and the middle of the outer shelf,
where the isotherms seem to extrude northward.
This extrusion may be attributed to the northeasterly
flow (West Alaskan Current: Favorite et al. 1976)
from Unimak Pass and the central Bering Sea along
the Alaska Peninsula, although it has been claimed
that there is no evidence of inflow toward inner
Bristol Bay along the Alaska Peninsula (Coachman
and Charnell 1979). In the bottom layer, the parallel-
ism of the 2.5- and 3-C isotherms with the 100-m
SURFACE
MID-APRIL,1978
r croRGE 1
■^o-
'-'
-^
:^v°-
--\
>. >
r "'
X
^"^^"^
"N
\
4.5'"
\
SURFACE
, LATE APRIL, 1978
-~"j<3.5
/
l-Kfr.
Figure 59-2. Isothermal distributions in the surface and bottom layers In the southeast Bering Sea, April 10-29, 1978.
Distribution of walleye pollock eggs 997
isobath was distinct, whereas isothermal distribution
seemed not to be related to the 200-isobath. The
northward extrusion of isotherms was not evidenced
in the bottom layer.
It is remarkable that the temperature gradient was
steeper over the inner shelf than over the outer shelf.
Isothermal distributions in the bottom layer depicted
a sharp gradient near the 100-m isobath. The dif-
ference of 2 C in the area between 160°W and 168° W
appeared to mark the steepest part of the gradient.
The temperature gradient along the 100-m isobath
was considered to correspond with the middle-shelf
front.
During the two phases, the surface layer with
temperatures of 2-3 C lay over a bottom layer with a
cold temperature of 1.5-2.5 C over the shallow shelf.
The 2.5-3.5 C temperature prevailed in the surface
waters of the outer shelf. Furthermore, the 4-C
isotherm extended to the bottom at the middle of
the outer shelf. Therefore, the temperature at the
bottom was higher over the outer shelf than the
surface temperature of 3-4 C; this condition produced
an inverted temperature structure. The temperature
difference between the two phases was about 0.5 C at
the surface, but neghgible at the bottom.
Relationships between temperature and salinity in
water masses at three depths for the four areas are
presented in Fig. 59-3. These are believed to exhibit
k
31,50
WATER TEMPERATURE "C
2.5 3.5
32.00
33.00
North Area
30 S s 30
Southeast
Area
3o<f>—n •
S: Surface
30; 30 m Layer
B: Bottom or 200 m Layer
O: Phase 1
• : Phase 2
Figure 59-3. Temperature-salinity relationship of the
three layers for the four areas.
representative values of temperatures and salinity
for this season. Each area showed a peculiar tempera-
ture and salinity range as well as vertical structure of
these properties. The north area over the inner shelf
was characterized by the lowest temperature (1.7-
2.3 C) and lowest salinity (31.9-32.0O/oo). The
uniformity in temperature and salinity from the
surface to the bottom layers implied that the water
mass of this area was vertically homogeneous and can
be identified as typical middle-shelf water (Ohtani
1969, Favorite et al. 1976, Coachman and Chamell
1977). In contrast to this area, the highest values
both in temperature (3.4-3.8 C) and salinity (32.4-
33.1°/oo) were evident in the southwest area over
the outer shelf and slope region. No remarkable
temperature changes were seen between the surface,
30-m, and bottom layers in the two phases. Salinity
was distinguishable between the surface and 30-m
layers and the bottom layer. Obviously, the bottom
layer bears the typical characteristics of oceanic
water, whereas the surface layer bears those of Alaskan
Stream water (Ohtani 1969). The water mass of the
southeast area north of Unimak Island was charac-
terized by high temperature (2.9-3.5 C) and the
lowest salinity (31.6-31.90/oo). Although the
salinity range of the bottom layer fell almost within
the same range as the north area, the temperature was
higher. While the lowest salinity values (31.6^/oo) in
the surface and 30-m layers are characteristic of
coastal water (Ohtani 1969), the bottom salinity
(31.9°/oo) was identical to that of the middle-shelf
water of the north area and the surface layer of the
northwest area. This is identified as West Alaska
Coastal water (Favorite et al. 1976). The northwest
area east of St. George Island exhibited a complicated
feature: the salinity range in the surface and 30-m
layers (31. 8-31. 9*^ /oo) was similar to that of the
north area and that of the bottom layer in the south-
west area, but the underlying bottom salinity (32.5-
32.7 o/oo) fell in the same range as the surface layer
of the southwest area. Essentially, the surface layer
was middle-shelf water and the bottom layer was
oceanic water.
Egg distribution pattern
A total of 86,859 eggs were obtained from 117
samples at 145 stations, compared to 45 walleye
pollock larvae from 11 samples, indicating that eggs
prevailed in the uppermost surface layer. The maxi-
mum abundance was 436 eggs/10 m* .
Fig. 59-4 presents the spatial distribution of eggs
by developmental stage in Phase 1. The egg distribu-
tion was not equal but continued through the stages.
The distribution patterns appeared basically to be
fl/V re THOMPSON CRUISE 131
PHASE I
APRIL 10 20, 1978
Figure 59-4. Distribution of walleye pollock eggs in the surface layer by developmental stage in Phase 1, April 10-20, 1978.
998
Dislhbulion of walleye pollock eggs 999
similar among eggs of Stages I-III and among eggs of
Stages IV-VI.
Stage-I eggs were mostly found in the north area
between 56°30'N and 57°N, and between 164°W and
168°W over the shallow shelf. There was an area of
great abundance with a maximum of 11 eggs/10 m^
at 57°N 166°W (Station 52, Fig. 59-1), where the
surface temperature was 2 C and bottom tempera-
ture was 1.6 C. Even eggs of Stages II and III were
later observed to be abundant at this station. Aside
from this major area, a discrete low abundance was
observed in the southeast area north of Unimak
Island, where the temperature was 3-3.5 C. There
were no eggs along the continental slope or in the
offshore region.
Stage-II eggs showed the widest distribution and
the highest abundance among the six developmental
stages. The eggs were distributed over most of
the shallow shelf and a considerable part of the
200-m shelf. The highest abundance, >100 eggs/
10 m^ , took place in two areas, 57°N and 166°W in
the north and 55°30'N and 164°W in the southeast
area. The maximum abundance of this stage reached
182 eggs/10 m' at Station 60 (Fig 59-1). The most
eggs were found in the area with surface tempera-
tures of 2-3 C and bottom temperatures of 1.5-
2.5 C. Unlike Stage-I eggs, a few eggs of Stage II (>1
egg/ 10 m^ ) were found in the southwest area south of
St. George Island, where the temperature was 3.5 C.
Most Stage-Ill eggs were taken from the shallow
shelf east of 168°W. Two abundant areas which
corresponded to those of Stage-II eggs were found
in the north and southeast. The abundance of this
stage reached a maximum of 159 eggs/10 m^ at
Station 60 (Fig. 59-1). In addition to this major
distribution, there were three separate egg distribu-
tions west of 167°W, all of which fell in the range of
the lowest abundance, 0.01-0.09 eggs/10 m\ The
temperature of the area of most abundant eggs was
2-3 C at the surface and 1.5-3.5 C at the bottom,
a somewhat warmer temperature range than that of
eggs of Stages I and II.
The distribution patterns of eggs of Stages IV-VI
resembled each other, but differed from those of
Stages I-III. The abundance decreased considerably
when compared with that of young eggs. The dis-
tribution of Stages IV-VI was confined to the shallow
shelf, and roughly delineated by the 2.5-C bottom
isotherm. A very abundant area (almost the same
as that of Stages II and III) was located only in the
southeast. The maximum abundance of these stages
did not exceed 12-17 eggs/10 m\ The tempera-
ture of the egg distribution area was 2-3 C in the
surface layer and 1.5-3 C in the bottom layer.
The distribution pattern in Phase 2 did not differ
greatly from that of Phase 1 (Fig. 59-5). Most eggs
were collected from the shallow shelf. In relation to
that in Phase 1 , the center of distribution shifted
slightly northwestward. One of the striking changes
in this phase was that the highest abundance of Stages
I-III disappeared from the north area near 57° N and
166°W. A relatively abundant area appeared in the
northwest near St. George Island; samples were
not taken in this area in Phase 1.
Stage-I eggs occurred in several isolated places over
the outer and inner shelves. An area of high abun-
dance was seen north of Unimak Island, but it was
narrow. The maximum abundance of this stage was
29 eggs/10 m' at Station 133 (Fig. 59-1). As in
Phase 1 , no eggs were observed along the continental
slope or in the offshore region. The surface temper-
ature seemed warmer, between 2 and 3.5 C, while
bottom temperatures remained the same, between 1.5
and 3 C.
Stage-II eggs were most widely distributed over
almost half the study area. As for Stage-I eggs, the
most abundant area was in the southeast. The
maximum abundance was 305 eggs/10 m^ at Station
133 (Fig. 59-1). An area of high abundance extended
north and west along the 100-m isobath. Another
area of relative abundance appeared east of St.
George Island. There were some eggs along the slope
south of St. George Island. The temperature range of
the egg distribution area was wider— between 2 and
4 C in the surface layer and 1.5 and 3.5 C in the
bottom layer, but most eggs were collected from
the 3-3.5 C range of surface temperatures. The 3.5-C
bottom isotherm coincided with the southern limit of
egg distribution.
Stage-Ill eggs were also distributed widely over the
area extending from Unimak Island northwest along
the 100-m isobath. The egg distribution ceased
at 168°W, and two isolated occurrences appeared in
the northwest and southwest areas adjacent to
St. George Island. Distribution was wider in this
phase than in Phase 1 . The two abundant areas found
north of Unimak Island and east of St. George Island
conformed to those of Stage-II eggs. The maximum
abundance was 102 eggs/10 m^ at Station 133 (Fig.
59-1). The temperature of the egg distribution area
was 2-3.5 C at the surface and 3-3.5 C at the bottom.
The distribution pattern of Stage-IV eggs resem-
bled that of Stages II and III, but the extent was
reduced to the shallow shelf. Unlike Stages I-III,
Stage-IV eggs were not found west of 168°W. Com-
pared with that in Phase 1, the distribution was
extended west. An area of high abundance remained
north of Unimak Island. The maximum abundance
R/vrC THOMPSOA/ CRUISE 131
PHASE 2
APRIL 21 29.1978
Figure 59-5. Distribution of walleye pollock eggs in the surface layer by developmental stage in Phase 2, April 21-29, 1978.
1000
Distribution of walleye pollock eggs 1 001
of 18 eggs/10 m^ occurred at Station 135 (Fig. 59-1).
There were no eggs along the slope. Most of the eggs
were taken from the temperature range of 2-3.5 C in
the surface layer and 1.5-3.5 C in the bottom layer.
The southern limit of distribution coincided with the
3-C bottom isotherm.
Eggs of Stages V and VI exhibited the narrowest
distribution and the lowest abundance of the six
developmental stages. The eggs were limited to
the shallow shelf between 164°W and 167°W; they
were not present over the shelf west of 167°W nor
along the continental slope. The maximum abun-
dance of these stages was 5 eggs/10 m^ at Station 134
(Fig. 59-1). The temperature range of the egg dis-
tribution area was 2-3.5 C in the surface layer and
1.5-3 C in the bottom layer. The southern limit of
distribution followed the 3-C bottom isotherm.
A high abundance of eggs over the shallow shelf
and the sparseness of eggs in the central and slope
regions led us to conclude that the spawming of
walleye pollock during the period from mid- to late
April of this year occurred primarily over the shallow
shelf. It can also be presumed that major spawning
populations did not exist along the continental slope
nor in the southwestern part of Unimak Pass. The
persistence of the distribution pattern and abundance
found throughout the two phases suggests that the
extent of spawning did not change greatly over a
relatively short period of time. It is apparent, how-
ever, that the distribution pattern of eggs differed
according to developmental stages, although the
extent overlapped considerably. Such difference in
distribution between the two phases indicates that
the spawning population shifted slightly from north
of Unimak Island to the northwest.
Eggs were encountered near the middle-shelf front
and coastal water zone, whereas few eggs were found
in oceanic water. The temperature regimes of the
main egg distribution area were 2-3.5 C in the surface
and 1.5-3.5 C in the bottom layers. No eggs were
found in warm bottom temperatures of 3.5-4 C.
The majority of eggs were found in salinity ranges
between 31.6 and 31.9°/oo. Only a few eggs were
observed between 32.4 and 32.5°/oo.
Mean relative abundance
Table 59-1 presents the mean relative abundance of
the eggs over the study area. Among the six devel-
opmental stages, Stage-II eggs were the most pre-
dominant with 14-15 eggs/10 m' , followed by
Stage III with 6-9 eggs. The combination of these
two stages reached as much as 83 to 88 percent of the
total. In contrast, eggs of Stages V and VI formed
the smallest fraction, 1 to 1.7 percent, or less than
TABLE 59-1
Mean relative abundance of walleye pollock in the number
of eggs/10 m^ over the study area by developmental stage
of the egg and by phase.
Phase 1
Phase 2
Mean
Stage
No.
%
No.
%
No.
%
I
1.58
5.6
1.04
4.4
1.31
5.0
II
14.24
50.2
15.09
63.6
14.67
56.3
III
9.28
32.7
5.71
24.1
7.50
28.8
IV
1.32
4.6
1.13
4.8
1.23
4.7
V
1.04
3.7
0.34
1.4
0.69
2.7
VI
0.90
3.2
0.41
1.7
0.66
2.5
TOTAL
28.36
100.0
23.72
100.0
26.06
100.0
one egg/10 m^ . Stage-I eggs showed only 1-1.6
eggs/10 m^ or 4-6 percent of the total. Likewise, the
abundance of Stage-IV eggs did not exceed 2 eggs/
10 m^ , or 5 percent. Thus, the mean relative abun-
dance amounted to 28 eggs/10 m^ in Phase 1 and 24
eggs in Phase 2, or a decrease of 14 percent during the
period between the two phases. Similarity in oc-
currence between the two phases suggests that the
eggs of respective developmental stages had similar
buoyancy.
Some of the developmental stages showed a
noticeable difference in percentage between Phase 1
and Phase 2. The proportion of Stage-II eggs in-
creased by about 14 percent in Phase 2 in spite of the
same abundance, whereas that of Stage-Ill eggs
decreased by 9 percent. The proportion of eggs of
Stages V and VI decreased to about half of Phase 1.
These results reflected an increased proportion of
eggs of the early stage in Phase 2.
The eggs of particular developmental stages were
not the same between the two phases, as the devel-
opmental stage advanced during the interval between
Phase 1 and Phase 2. Using the relationship between
water temperature and age of an egg we can deduce
the interrelationship of developmental stages between
the two phases (Table 59-2). Most eggs of Stages I
and II in Phase 1 would advance to Stage III in
Phase 2. Stage- V eggs in Phase 2 are assumed to
have been mostly Stage-Ill eggs in Phase 1. A few
Stage-Ill eggs in Phase 1 would advance to Stages IV,
V, and VI in Phase 2. Further, Stage-IV eggs in Phase
2 might have partly originated from Stage II in Phase 1 .
Stages IV-VI in Phase 1 would not have been col-
lected in Phase 2, because these would have hatched
before Phase 2. On the other hand, eggs of Stages I
and II in Phase 2 have been laid in this phase. Thus
Stages IV-VI in Phase 1 and Stages I and II in Phase 2
are assumed to have originated from different spawn-
ing populations.
1002 Plankton ecology
TABLE 59-2
Assumed relation of egg developmental stage between
the two phases.
Phase I
Phase 2
Stage I
Stage V ) Hatched out~
in Phase 1
Stage VI *
Stage I
Stage II
Stage III
Stage IV
Stage V
Stage VI
Newly laid
in Phase 2
N X SD
Phase! 101 1.778 0.070
I I Phase 2 372 1.743 0.083
Taking into account the advancement of egg
development between the two phases, we can com-
pare the abundance of some particular developmental
stages during the two phases. While eggs of Stages I
and II in Phase 1 remained 37 percent as Stage-Ill
eggs in Phase 2, Stage III eggs in Phase 1 dropped to
as low as 14 percent when they advanced to Stages
IV- VI in Phase 2, even though it required almost the
same length of time for these two groups to advance
to consecutive stages (6-7 days at 3 C). Furthermore,
the magnitude of reduction during the advancement
from Stage III to Stage IV was 3.3 times greater than
that during the advancement from Stage II to Stage
III. Thus, the change in abundance of the eggs is
considered to be related to the difference of mor-
tality and buoyancy of the developmental stages.
Egg diameter
Fig. 59-6 shows the frequency distributions of
egg diameters observed in the present study. The
range of egg diameters extended from 1.325 to
STAGE IV
^_^ N X SD
1 1 1 1 1 1 1 Phase 1 36 1.738 0.096
cu
Phase 2 129 1.750 0.080
1375 1.475 1575 1.675 1.775 1.875
STAGE V
N X SD
lllllll Phase 1 30 1 .753 0.084
1 I Phase 2 42 1.749 0.097
_1_
1375 1475 1.575 1.675 1775 1875
STAGE VI
rr-rrrr, N X SD
lllllll Phase 1 32 1.733 0.078
I I Phase 2 67 1.756 0.066
DIAMETER OF E G G (mm) DIAMETER OF E G G (mm)
Figure 59-6. Frequency distribution of egg diameter of walleye pollock by developmental stage and by phase.
Distribution of walleye pollock eggs 1003
1.925 mm. From the figure, it can be assumed that
the egg diameter is normally distributed. Chi-square
tests for goodness-of-fit indicate that in most cases
the normal distribution is accepted at the 95-percent
probability level (P > 0.05), but for Stage-II eggs (P
< 0.01) and Stage-III eggs {P < 0.05) in Phase 1.
In Phase 1, the mean egg diameter was 1.733 mm
for Stage-VI eggs and 1.778 mm for Stage-III eggs.
Although there was a slight difference in the mean
among the six developmental stages, no particular
tendency was observed between the means and stages.
Application of normal curve statistics (Z-value) to all
pairs of means showed no statistical significance
among the stages except for the Stage-III eggs (Table
59-3). The variance ratio (F) of each pair was not
statistically significant at the 1 -percent level (P =
0.01). The mean diameter of Stage-III eggs was
statistically different from those of Stages I, II, IV,
and VI at the 5-percent level (P = 0.05), but not from
that of Stage V. The reason Stage-III eggs are largest
is not clear. An asymmetric distribution suggests that
this effect might be derived partly from a compli-
cated egg-size composition with different spawning
populations and partly from the sampling bias.
In Phase 2, the mean egg diameter tended to be
larger in older eggs: the mean was smallest in Stage I
and largest in Stage VI (Fig. 59-6). The variance ratio
of each pair was not significant at the 5-percent level
(P = 0.05), but it was significant for the pairs between
Stage-VI eggs and the eggs of other stages. The values
of Z indicated that the difference of the means was
significant between Stage-I eggs and the other stages
(Table 59-3). Furthermore, the mean of Stage-II eggs
was also statistically different from those of the
remaining stages except for Stage V. On the other
TABLE 59-3
Comparison of differences between all pairs of mean egg
diameters in Phase 1 and Phase 2. A value of Z is given
when a statistically significant difference occurs in a
comparison at the 5 percent (*), 1 percent (**), and 0.1
percent (***) levels; NS denotes no significant difference
indicated in a comparison.
II
Developmental stage of egg
III IV V
VI
I -
2.24* 3.65*** 3.85*** 2.82** 4.81**
II
NS
3.70*** 3.48***
III 4.04*** 3.74***
IV NS
V NS
VI NS
I—
NS
NS
NS
2.30*
NS
2.90**
NS
NS
NS
NS
3.78**
NS
NS
NS
NS
—
NS
NS
hand. Stages IV-VI did not show statistically signifi-
cant differences.
Comparison of the mean egg diameter of the same
stage between the two phases indicated that eggs of
Stages I-III in Phase 1 were larger than those in
Phase 2. The difference of the means was statistically
significant (Table 59-4). No difference was found in
eggs of Stages IV-VI. The variance ratio between
pairs was not significant at the 1-percent level (P =
0.01).
TABLE 59-4
Comparison of difference of mean egg diameter between the
two phases by egg developmental stage. A value of Z is
given when a statistically significant difference occurs
in a comparison at the 5-percent (*), 1-percent (**), and
0.1-percent (***) levels; NS denotes no significant difference
indicated in a comparison.
II
Developmental stage of egg
III IV
VI
2.71*
4.83***
427***
NS
NS
NS
Phase 1
Fig. 59-7 illustrates the frequency distributions of
egg diameters for the three areas; the data for all the
stages were combined. Data were unavailable for the
northwest area in Phase 1 and the southwest area in
both phases because of small sample size. The
histograms assume normal distributions except for
the southeast area in Phase 1, in which a chi-square
test for normal distribution did not show the best fit
at the 95-percent level (P < 0.001). The means of the
southeast and north areas in Phase 1 seem to fall
within a similar range. This was ascertained by the
test of difference of the means, as indicated in Table
59-5, in which no statistically significant difference
was found between these two areas. However, in
Phase 2, the mean egg diameter found in the north
area was larger than in the southeast and northwest
areas. The difference of the means was significant
(Table 59-5). No statistically significant difference
was observed between the southeast and northeast
areas in Phase 2. It is apparent that the mean egg
diameter of both southeast and north areas became
smaller in Phase 2. The difference of the means was
statistically significant (Table 59-6).
To confirm the difference in egg size of the same
developmental stage between the two phases, the
mean diameter of Stage-II eggs was compared for
each area. From Table 59-7 it is obvious that the
mean egg diameter tended to decrease during the
period from Phase 1 to Phase 2. The test of the
difference indicated that the difference of the means
1004 Plankton ecology
- SOUTHEAST AREA
rrrrrm N x SD
llllllll Phase 1 86 1.760 0.075
r~i
Phase 2 222 1.710 0.098
1.375 1.475 1.675 1.676 1.775 1.876
NORTH AREA
N X SD
llllllll Phase 1 215 1.764 0.085
{,_J Phase 2 47 1.739 0.067
lllllin I 'Illlll
1.575
1 775
DIAMETER OF EGG (mm)
Figure 59-7. Frequency distribution of egg diameter of
walleye pollock by area and by phase.
was statistically significant between the two phases
except in the southwest area (Table 59-8).
Comparison of the mean egg diameter of a pair of
developmental stages assumed to be laid by the same
spawning population was attempted over the two
phases. As seen in Table 59-9, there was no statis-
tically significant difference in the means in most
TABLE 59-5
Comparison of the difference of mean egg diameter between
all pairs of mean egg diameters in Phase 1 and Phase 2.
A value of Z is given when a statistically significant
difference occurs in a comparison at the 5-percent (*), 1-
percent (**), and 0.1-percent (***) levels; NS denotes
no significant difference indicated in a comparison.
Areas
Phase 1
Phase 2
Southeast-North
Southeast-Northwest
North-Northwest
NS
2.46*
NS
1.98*
cases. Exceptions were the pairs between Stage-Ill
eggs in Phase 1 and eggs of Stages IV and VI in
Phase 2. However, since most Stage-Ill eggs were
considered to have advanced to Stage V in Phase 2, it
will be safe to conclude that there was no significant
difference in egg size when Stage III eggs in Phase 1
advanced to Stage V in Phase 2. Table 59-10 presents
the results of comparing the means of the two de-
velopmental stages which are assumed to have orig-
inated from different spawning populations. It is
apparent that each combination of a pair shows a
TABLE 59-6
Comparison of the difference of mean egg diameters of the
two areas between Phase 1 and Phase 2. A value of Z is
given when a statistically significant difference occurs
in a comparison at the 5-percent (*), 1-percent (**),
and 0.1-percent (***) levels; NS denotes no significant
difference indicated in a comparison.
Area
Southeast
North
4.80***
2.20*
TABLE 59-7
Mean egg diameter of Stage-II eggs by phase and by area.
Area
X
+
SD
Phase 1
(n)
Range
X
+
SD
Phase 2
(n)
Range
Southeast
1.756
+
0.077
(81)
1.575-1.875
1.707
±
0.092
(211)
1.375-1.925
Southeast
1.719
+
0.078
(18)
1.575-1.875
1.716
+
0.063
(22)
1.625-1.875
North
1.765
+
0.086
(127)
1.425-1.875
1.728
+
0.085
(74)
1.475-1.875
Northwest
1.747
+
0.068
(58)
1.625-1.875
1.721
+
0.083
(109)
1.525-1.875
Distribution of walleye pollock eggs 1005
TABLE 59-8
Comparison of difference of mean egg diameter of Stage-II
eggs between Piiase 1 and Phase 2. A value of Z (or t) is
given wiien a statistically significant difference occurs
in a comparison at the 5-percent (*), 1-percent (**), and
0.1-percent (***) levels; NS denotes no significant difference
indicated in a comparison.
Area
Southeast
Southwest
North
Northwest
4.60***
NS
2.97**
2.19*
statistically significant difference, except Stage-IV
eggs in Phase 1 and Stage-II eggs in Phase 2.
The results can be summarized as follows: there
was no difference in egg size among the develop-
mental stages in the early season, except Stage-Ill
eggs which showed the largest egg size; but a consid-
erable difference arose in the late season. Egg size
tended to decrease in young eggs and in the late
season. Geographically, egg diameter was smaller in
the southeast area than in the north area. The egg
size did not change when the developmental stage
advanced during the period from Phase 1 to Phase 2.
The egg size was larger in old eggs in the early season
and smaller in young eggs in the late season.
TABLE 59-9
Comparison of the difference of mean egg diameters of a
pair of developmental stages between two phases in which
the eggs are assumed to be laid by the same spawning
population. A value of Z is given when a statistically
significant difference occurs in a comparison at the 5-percent
(*), 1-percent (**), and 0.1-percent (***) levels; NS denotes
no significant difference indicated in a comparison.
Phase 1
Phase 2
Stage I
Stage II
Stage II
Stage III
Stage III
Stage III
Stage III
Stage III
Stage IV
Stage IV
Stage V
Stage VI
NS
NS
NS
2.83**
NS
2.06*
TABLE 59-10
Comparison of the difference of mean egg diameters of a pair
of developmental stages between Phase 1 and Pha.se 2 in which
the eggs are 'assumed to originate from different spawning
populations. A value of Z is given when a statistically sig-
nificant difference occurs in a comparison at the 5-percent
(*), 1-percent (**), and 0.1-percent (***) levels; NS denotes
no significant difference indicated in a comparison.
Phase 1
Phase 2
Stage IV
Stage IV
Stage V
Stage V
Stage VI
Stage Vi
Stage I
Stage II
Stage I
Stage II
Stage I
Stage II
2.18*
NS
3.48***
2.98**
2.11*
3.79***
DISCUSSION
Distribution pattern
Laboratory observations have shown that walleye
pollock eggs float wdth high buoyancy in the surface
layer of sea water after fertilization until hatching
takes place in the normal salinity range (Gorbunova
1954, Kanoh 1954, Yusa 1954a). In nature, how-
ever, most of the eggs have been collected from
the subsurface (Gorbunova, 1954, Ito et al. 1955,
Ogata 1956, Serobaba 1975, Maeda and Hirakawa
1977, Mattson and Wing 1978). Eggs have even been
collected from the depths of 2,700 m in East
Kamchatka (Gorbunova 1954) and 1,000 m in the
eastern Bering Sea (Serobaba 1975). On the shelf and
in the embay ment, the eggs appeared to occur in the
near-surface layer; egg concentrations have been
observed in the upper 1-m layer (Ito et al. 1955,
Takeuchi 1972, Kamba 1977). In the eastern Bering
Sea, Serobaba (1975) reported that the eggs were
distributed from the surface to the 100-m layer with
a peak between the surface and 20-m layers;
Musienko (1963) stated that the eggs develop in the
upper 1-10 m. From these findings, it is obvious that
walleye pollock eggs are pelagic and drift in all water
layers between the surface and a considerable depth.
In this respect, the walleye pollock is unlike the two
other members of the family Gadidae in the southeast
Bering Sea^ Pacific cod {Gadus macrocephalus) and
saffron cod {Eleginus gracilis), which lay demersal
eggs.
1 006 Plankton ecology
Waldron and Vinter (1978) estimated that less than
1 percent of the total walleye pollock eggs found
below the water column (<0.25 m) occur as neuston.
Similarly, it has been reported that the eggs of plaice,
Pleuronectes platessa, in the uppermost layer formed
less than 1 percent of the plaice eggs found in the
entire water column (Pommeranz 1973). These
estimates show that only a small fraction of pelagic
eggs occur as neuston. Therefore, walleye pollock
eggs appear as neuston in the uppermost surface layer
under particular conditions. The abundance and
structure of vertical distribution of pelagic eggs varies
depending upon biotic and abiotic factors. Works of
Simpson (1956), Zaitsev (1964, 1971), Nellen and
Hempel (1970), Hempel and Weikert (1972), and
Pommeranz (1973) have shown that wind force and
wave action are the most influential factors determin-
ing the abundance and vertical stratification of
fish eggs. Furthermore, the buoyancy of eggs and
their resistance to wave disturbance appear to be
species-specific and to depend upon the develop-
mental stage of the eggs (Zaitsev 1971). At present
we lack knowledge about the relation of wind force
and turbulence of sea water to the buoyancy of
walleye pollock eggs in nature. Instability in the
buoyancy of eggs may modify the distribution
pattern and abundance of eggs observed in the
present study. However, in view of the persistence of
characteristics of distribution patterns and abun-
dance, it is clear that fundamental features of distri-
bution are not significantly influenced.
Although use of neuston surveys limits quantitative
comparison, it is an easy and appropriate way of
studying the spawning ground of fish (Smith and
Richardson 1977). Previous studies have indicated
that the spawning of walleye pollock takes place over
the outer shelf, along the continental slope, and even
in the offshore region, from late February through
mid-June. Serobaba (1968) reported that the eggs
were aggregated over the outer shelf near Unimak
Pass. Maeda and Hirakawa (1977) stated that a high
concentration of eggs occurred near Unimak Pass.
These works have shown a simple pattern of egg
distribution: the eggs seemed to be laid in a single
high concentration near Unimak Pass, and then
dispersed centrifugally from the deeper region to a
shallow region. Compared with these previous
results, the egg distribution observed in our data has
revealed more complicated features, even though
the discrepancy in distribution pattern may be partly
attributed to the differences in sampling methods and
temporal and spatial scale of sampling. We conclude
that a major spawning took place mainly over the
inner shelf in mid- and late April of the study year.
The concurrence of spawning over the wide area
along the slope and over the outer shelf seems to be
unlikely. The fundamental pattern of egg distribu-
tion took the form of a wide belt over the inner shelf
along the bottom contour, although spawning ap-
peared to occur in several isolated locations over
the shelf.
Close spacing and duplicate samplings with a
neuston net, as employed here, seem to be appro-
priate to clarify spav^ming and characteristics of the
egg distribution pattern. Particularly, the analyses of
neustonic occurrence of eggs by developmental stages
will allow us to conjecture the spawning location,
dispersion, assessment of environmental regime, and
the area of hatching larvae.
Although it is very hkely that in 1978 the
major spawning occurred over the inner shelf in mid-
and late April, it is possible that the spawning took
place along the slope and offshore in the early season.
In mid-February through mid -March, Waldron (1978)
found that the eggs occurred sporadically, occa-
sionally in great abundance along the slope, whereas
they were very scarce over the shelf. In April, a
relatively high abundance of larvae accompsinying
only a few eggs was found in the deep region along
the slope and partly over the outer shelf (Cooney et
al. 1979). Despite a high abundance of eggs, larvae
were not caught over the shallow shelf during this
season. This evidence confirms the existence of a
dense spawning population along the slope in the
earlier season, but not over the shallow shelf. Conse-
quently, questions arise as to whether the spawning
population in the offshore area in the early season is
the same as that over the shallow shelf in the late
season. To examine this problem, it is necessary to
take into account the duration of the spawning
period and the movement of walleye pollock. On the
basis of histological examination of oogenesis in
walleye pollock, Yoon (1977) concluded that a single
female lays eggs at least twice or more in a month.
Later, Yoon (1979) confirmed that walleye pollock
females in captivity spawned two to five times at
intervals of 2-7 days in an 18-day spawning period.
The number of eggs released at one time varied from
6,000 to 28,400, with a slight decrease at the later
spawning. These findings indicate that the spawning
period of walleye pollock lasts a relatively long time.
Waldron (1978) has assumed that the spawning
population remains in the deep region for about
20 days in February and March. If this is true,
presumably the spawning population does not mi-
grate to a great extent and spawns more than once in
the same location, and hence a relatively high abun-
dance of eggs might be expected to occur along
Distribution of walleye pollock eggs 1007
the slope and in the offshore region in mid-April.
However, only a few eggs were obtained along the
slope in the present study. Thus, this possibility
seems to be doubtful, although we lack data on egg
distribution during the period from mid-March
through early April. This leads us to consider another
possibility: that the spawning population migrates
from one spawning area to another. Tag-release and
recovery experiments on the feeding population,
conducted for a relatively short period of time,
indicate speeds of 13-17 km/d in the Japan Sea
(Ogata 1956) and 5-7 km/d in the eastern Bering Sea
(Yamaguchi 1972). Taking into consideration the
speed of migration and the distance between the
slope and the shallow shelf, and assuming that these
speeds of migration are applicable to the spawning
population in the study area, we can conclude that
the same spawning population spawns early along the
slope and in the offshore region and then migrates to
the inner shelf for later spawning. The validity of
these assumptions, however, awaits further analyses
of data concerning spawning behavior, migration, and
population structure, as well as a comparison of the
characteristics of eggs and larvae between the early
and late spawning populations.
The annual fluctuation of egg distribution of
walleye pollock and hydrographic conditions has
been reported in Uchiura Bay, Hokkaido (Ito et al.
1955) and Peter the Great Bay (Bezludny 1979).
Despite many reports on the long-range fluctuations
of oceanographic and climatic conditions (Maeda et
al. 1967, 1978; Maeda 1972; McLain and Favorite
1976), little is known about annual fluctuations of
temperature during the spawning period of walleye
pollock in the southeast Bering Sea. Serobaba (1975)
reported that the predominant surface temperature
was 2 C over the outer shelf in 1965. Maeda and
Hirakawa (1977) showed that the prevailing bottom
temperature was 1-3 C in 1972 and 2-3.5 C in 1973.
Both surface and bottom temperatures were higher in
the present study than in these previous years. Such
temperature differences may cause a difference in the
extent of the spawning area, and hence in the egg
distribution pattern.
The coincidence of egg distribution and iso-
thermal patterns suggests that the bottom isotherm
plays a role in determining the extent and duration of
spawning. Particularly, the 3-C bottom isotherms
appeared to be most significantly related to the
delineation of egg distribution. Serobaba (1968)
found the spawning aggregation of walleye pollock
near waters at temperatures of 2.5-3 C. Maeda and
Hirakawa (1977) showed that a high concentration of
eggs was associated with the bottom temperatures of
2.5-3 C. Since the 3-C isotherm areas corresponded to
the middle-shelf front, it is possible that the hydro-
graphic conditions of the outer-shelf zone and middle-
shelf front have limited the extent of distribution
of the spawning population, and hence the extent of
egg distribution. At this time, the temperature
gradient near the front may play a role in guiding the
spavining population, rather than actual particular
temperature ranges. Lack of temperature data for the
early season along the slope prevents an extended
discussion of the relationship between the early
spawning population and the hydrographic regime of
this region.
Mean relative abundance
Consistency of proportion of the six develop-
mental egg stages, the widest distribution, and the
highest abundance of Stage-H eggs during the two
phases deserve consideration. The neutral buoyancy
of fertilized eggs of walleye pollock has been reported
to be equivalent to sea- water density (sigma-t) of
21.3-25.1 (Kanoh 1954, Yusa 1954b, Ogata 1956).
Since the sea-water density of the study area was
25.0-25.8, the eggs can be expected to float in the
surface layer. If the buoyancy and mortality rate of
eggs are the same among the six developmental stages,
the proportion of occurrence is expected to be
greatest in Stage I. It is also anticipated that the
number of eggs in each stage will gradually decrease
from the youngest stage to the oldest stage. And yet,
Stage-I eggs were only 5 percent of the total. Fur-
thermore, Stage-I eggs in Phase 1 increased by four
times when they advanced to Stage III in Phase
2. Such an increase seems contradictory. Therefore,
it is possible that the proportion of occurrence may
be derived from the changes in buoyancy and mortal-
ity during the development of eggs. We assume that
buoyancy is higher in eggs of Stages II and III than in
the other stages. It is conceivable that Stage-I eggs
are characterized by weak buoyancy and slow rising
speed after fertilization. It is not known how fast the
fertilized eggs of walleye pollock rise to the surface
layer from the layer where the eggs are laid on the
shelf. We can refer to the data about other members
of the family Gadidae. Steward and Brook (1885)
have observed that eggs of the Atlantic cod, Gadus
morrhua, rose slowly through the water at the rate of
48 cm/hr. Jensen (1972) noted that eggs of the
haddock, Melanogrammus aeglefinus, rose at the rate
of 109 cm/hr. If this rising speed of eggs is apphcable
to walleye pollock eggs, it seems impossible for
Stage-I eggs to arrive at the surface within a short
period of time. We therefore suppose that most of the
Stage-I eggs with the upward-directed buoyancy
1008 Plankton ecology
remained in the subsurface layer. This would result
in a small fraction of neustonic occurrence of Stage-I
eggs, and may also partly explain why Stage-I eggs
were not found along the slope despite the apparent
occurrence of eggs of Stages II and III.
Little is known of the relationship between specific
gravity of eggs and the developmental stages of
walleye pollock, even though Gorbunova (1954)
has stated that walleye pollock eggs sink to a greater
depth in the course of development. However, it is
probable that the decreased abundance of eggs of
Stages IV-VI resulted from the reduced buoyancy of
old eggs. Of Atlantic cod, Sundness et al. (1964)
observed that the specific gravity of eggs steadily
increased during development until hatching. They
also found that the buoyancy of these eggs was
independent of water pressure and temperature, but
markedly influenced by salinity.
High mortality is known to occur at particular
developmental stages of fish eggs. Russel (1976)
stated that the closure of the blastopore marks the
end of a critical period in development. Yusa
(1954a) observed that the highest mortality in
walleye pollock eggs occurred in the first gastrulation
stage. On the southeast coast of Hokkaido, Kyushin
(personal communication) found that most of the
dead eggs of walleye pollock taken from the surface
layer belonged to the morula /first -gastrulation stages.
These findings suggest that there was high mortality
during the progress of eggs of Stages II and III in
this study. This may be a reason for the low abun-
dance of eggs of Stages IV-VI.
It is reasonable to consider that the combined
effects of the changes in buoyancy and mortality, due
to vulnerability and susceptibility by developmental
stage, are involved in the varying proportions of
occurrence of different developmental stages. The
assumption of high buoyancy in Stages II and III,
reflecting the strong neustonic nature of these stages,
must be tested by examining the vertical distribution
and abundance of eggs in the water column. The
instability of egg buoyancy due to mechanical turbu-
lence of wind and wave action also needs to be
clarified.
Egg diameter
Egg diameter of walleye pollock varies between 1 .2
and 2.4 mm in various geographic areas (Kamiya
1925, Yamamoto and Hamashima 1947, Gorbunova
1954, Yusa 1954a, Takeuchi 1972). Serobaba (1968)
reported egg diameters from the eastern Bering Sea to
be from 1.46 to 1.64 mm. The range of egg diam-
eters observed in this study extended from 1.325 to
1.925 mm, a wider range than that given by
Serobaba.
It is also known that the size of walleye pollock
eggs does not change in the course of development
(Gorbunova 1954, Yusa 1954a, Fukuchi 1976).
However, egg size appears to be related to the size of
the female. Ogata (1956) described the egg size in
walleye pollock as larger in old females than in
young females. Serobaba (1968) demonstrated that
egg size in the eastern Bering Sea varied from March
through July, tending to decrease. Serobaba attrib-
uted the cause of decrease in egg size to a reduction
in the size of spawning females as the season pro-
gressed. In compiling published data, Bagenal (1971)
concluded that the size of fish eggs fluctuates in a
single species with the season, with a general ten-
dency toward seasonal decline. If this generalization
is accepted, we can assume that the larger eggs in
Phase 1 were laid by larger females and that the
larger eggs in the north area were laid by females
larger than those in the southeast area. From exten-
sive trawl-survey data, Yamaguchi (1979) indicated
that in June walleye pollock 50-60 cm in length
were caught over the inner shelf 50-80 m deep,
whereas those of 40-50 cm were caught over the shelf
100-200 m deep. These data indirectly support the
existence of a spawning population of larger size over
the inner shelf.
The difference in egg diameters reflects the volume
and weight of the eggs. Using Fukuchi's data (1976),
Nishiyama (in preparation) presented empirical
equations demonstrating the relationship of egg
size to the volume and wet and dry weights of wall-
eye pollock. According to the equations, the differ-
ence in egg diameter between the smallest egg (1.325
mm) and the largest egg (1,925 mm) in this study
results in differences in volume of 3.1 times, 2.2
times in wet weight, and 2.5 times in dry weight. The
data on egg diameter and larval size (Kamiya 1925,
Yamamoto and Hamashima 1947, Gorbunova 1954,
Yusa 1954a, Hamai et al. 1971, Fukuchi 1976)
suggest an increasing tendency of the larger larvae to
hatch from the larger eggs. These differences are
significant both physiologically and ecologically for
survival and growth of hatching larvae. Ware (1975,
1977) discussed the difference of fish-egg size relative
to the size of larvae and size of food organisms taken
by the hatching larvae. It is assumed that the larger
eggs in Phase 1 and eggs of Stages IV-V in Phase 2 will
produce larger larvae than smaller eggs of Phase 1 and
of Stages I-III in Phase 2. The north area and south-
east area will also produce larger larvae than the other
areas. Seasonal and geographical differences in egg
size must be investigated in relation to the egg incu-
bation period, yolk-absorbing period, and food
availability for hatching larvae.
Distribution of walleye pollock eggs 1009
ACKNOWLEDGMENT
This study, Contribution No. 418, Institute of
Marine Science, University of Alaska, is one of a
series of interdisciplinary research projects on Proc-
esses and Resources of the Bering Sea (PROBES),
funded by the Division of Polar Program of the
National Science Foundation under Grant No.
DPP762340 to the University of Alaska. The authors
wish to express their gratitude for the opportunity
for study and for encouragement received from
Drs. D. Hood, P. McRoy, and J. Goering. The writers
gratefully acknowledge helpful suggestions from
Drs. M. Fukuchi, K. Kyushin, and T. Cooney during
this work. Our thanks also to the captain and crew of
the R/V Thomas G. Thompson for their cooperation
on board in collecting the present material. Thanks
are also due to Mrs. Helen Stockholm for correcting
the manuscript.
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Section XI
I Fisheries Biology
Murray Hayes, editor
Commercial Use and Management
of Demersal Fish
R. Bakkala, K. King, and W. Hirschberger
National Oceanic and Atmospheric Administration
National Marine Fisheries Service
Northwest and Alaska Fisheries Center
Seattle, Washington
ABSTRACT
Commercial exploitation of demersal fish in the eastern
Bering Sea began almost 100 years ago, when U.S. fishermen
began harvesting Pacific cod (Gadus macrocephalus). The next
fishery to develop in the region (in 1928) was the U.S. and
Canadian fishery for Pacific halibut (Hippoglossus stenolepis).
In the twenty years that followed, halibut operations were
sporadic, and the North American cod fishery declined both in
number of vessels and catch. Between 1950 and the late
1970 's domestic fishing for groundfish in the eastern Bering
Sea was almost entirely limited to a setline fishery for Pacific
halibut. The Japanese initiated a trawl fishery in the mid-
1930 's for pollock and flounders off Bristol Bay, but these
efforts were interrupted by the Second World War. The
Japanese resumed trawling operations in the eastern Bering Sea
in 1954, targeting on yellowfin sole (Limanda aspera) off
Bristol Bay. The U.S.S.R. joined in this fishery in 1958.
Japanese and Soviet fisheries expanded throughout the eastern
Bering Sea in subsequent years, utilizing a wide variety of
demersal species. The Republic of Korea in 1967 and Taiwan
in 1974 also sent trawlers to the eastern Bering Sea. Beginning
in the mid-1960's, walleye pollock (Theragra chalcogramma)
became the major target species of foreign fisheries, and total
catches of demersal fish rose sharply as exploitation of this
large resource intensified. At their peak, landings by foreign
fisheries in the eastern Bering Sea were among the world's
largest, supplying more than 2 million mt of groundfish
annually.
As evidence accumulated in the 1970's of a decline in
abundance of some of the eastern Bering Sea resources, catch
restrictions were placed on foreign fisheries, first through
bilateral agreements between the U.S. and user nations, and
later through the U.S. Fishery Conservation and Management
Act (FCMA) of 1976. Foreign catches in 1977 and 1978
ranged from 1.0 to 1.3 million mt.
With implementation of the FCMA in March 1977, all
fishery resources within 200 miles of the Alaskan coast came
under the direct jurisdiction of the United States. The specific
objectives of the management plan developed for the eastern
Bering Sea and Aleutian Islands region are to: (1) continue
rebuilding the Pacific halibut resource; (2) rebuild depleted
groundfish stocks and maintain healthy stocks at levels that
will produce maximum sustainable yields; (3) promote the
participation of U.S. fisheries in the use of the resources; and
(4) allow continued foreign use of the resources consistent
with the first three objectives.
INTRODUCTION
The resource of demersal fish in the eastern Bering
Sea is large; at the peak of foreign fishing (1971-74),
annual catches ranged from 2.0 to 2.2 million metric
tons (mt). Geographic, climatic, and oceanographic
conditions (discussed in other chapters) combine to
create an environment favorable for supporting the
large populations of demersal fish (in addition to
some of the world's largest bird and marine mammal
populations) found in the Bering Sea. Although the
processes are not fully understood, these large popu-
lations are probably sustained by the upwelling of
nutrient-rich water along the south side of the Aleutian
Islands and subsequent mixing of Pacific Ocean and
Bering Sea water, the seasonal extremes in climate
in the Bering Sea with a build-up of nutrients during
the winter months, and the extensive habitat created
by the large continental shelf in the eastern Bering
Sea (Gershanovich et al. 1974, Sharma 1974).
Most of the commercially important demersal
fish of the eastern Bering Sea inhabit the continental
shelf and slope from the Alaska Peninsula and eastern
Aleutian Islands to the latitude of St. Matthew Island
(Fig. 60-1). Most of this region lies within the U.S.
200-mile fishery conservation zone, and since 1977
the resources have been managed through the U.S.
Fishery Conservation and Management Act (FCMA)
of 1976. Mainly foreign fisheries have exploited the
resources commercially. This chapter will review the
history of the foreign and North American fisheries in
this region, the apparent effect of the fisheries on the
resources, and current management policies.
1015
1016 Fisheries biology
Figure 60-1. Geographical locations in the Bering Sea.
COMMERCIAL SPECIES
NORTH AMERICAN FISHERIES
The Bering Sea supports about 300 species of
fish, most of which live on or near the bottom
(Wilimovsky 1974). About 24 species from the
demersal or semidemersal group are presently used
as food fish. Only six species, because of their
abundance or high market value, are consistently
targeted by foreign and domestic fisheries; five more
species are occasionally targeted (Table 60-1). The
13 remaining species are relatively sparse, and they
form only an incidental part of catches. Incidental
catches of nonfood fish, such as sculpins (family
Cottidae), may be reduced to fish meal along with
wastes from filleting operations and undersized food
fish.
A summary of the biological characteristics of the
most important commercial species is given in Table
60-2.
Although the use of Bering Sea bottomfish re-
sources by U.S. and Canadian fishermen has been
relatively minor, fishing activities date back more
than a hundred years. Pacific cod was the first
species taken, initially in the course of an exploratory
effort involving a single schooner in 1864, and then
annually starting in 1882. Vessels operated from
ports in Washington and California and from shore
stations in the eastern Aleutian Islands (Cobb 1927).
Canadian vessels also participated in the fishery to a
limited extent. Throughout its history, the Bering
Sea cod fishery was conducted largely by sailing
schooners, and fishing was by handlines from one-
man dories. Fishing areas extended along the north
side of Unimak Island and the Alaska Peninsula to
Bristol Bay from depths of about 25-100 m (Cobb
1927).
Demersal Fish 1017
TABLE 60-1
Demersal species in the eastern Bering Sea
used as food fish by foreign and domestic fisheries.
Common name
Scientific name
Species consistently targeted
Pollock
Pacific ocean perch
Sable fish
Yellowfin sole
Greenland turbot
Pacific halibut
Species occasionally targeted
Pacific cod
Rock sole
Flathead sole
Arrowtooth flounder
Rattails
Species incidentally caught^
Atka mackerel
Rougheye rockfish
Dusky rockfish
Northern rockfish
Shortspine thomyhead
Shortraker rockfish
Alaska plaice
Rex sole
Butter sole
Longhead dab
Dover sole
Starry flounder
Skates
Theragra chalcogramma
Sebastes alutus
Anoplopoma fimbria
Limanda aspera
Reinhardtius hippoglossoides
Hippoglossus stenolepis
Gadus macrocephalus
Lepidopsetta bilineata
Hippoglossoides elassodon
Atheresthes stomias
Coryphaenoides spp.
Pleurogrammus monopterygius
Sebastes aleutianus
S. ciliatus
S. polyspinis
Sebastolobus alascanus
Sebastes borealis
Pleuronectes quadrituberculatus
Glyptocephalus zachirus
Isopsetta isolepis
Limanda proboscidea
Microstomas pacificus
Platichthys stellatus
Raja spp.
^Includes species that may be marketable as food fish but
are not targeted because of their low abundance. Because
of problems in identifying rockfish, the species listed may
be incomplete or contain species not actually occurring
in the eastern Bering Sea.
The North American cod fishery reached its peak
during World War I, when estimated annual catches
ranged from 12,000 to 14,000 mt (Table 60-3).
In contrast, the large foreign fishery has annually
taken about 50,000 mt of Pacific cod from the
eastern Bering Sea in recent years. After 1920,
numbers of North American vessels and their catches
gradually declined until the fishery ended in 1950.
Although cod fishermen reported the presence of
Pacific halibut in the Bering Sea as early as the
1800's, this species was not harvested commercially
until 1928 (Thompson and Freeman 1930). Com-
mercial fishing for Pacific halibut in the eastern Bering
Sea was sporadic in the 1930's and 1940's. The
fishery began on an annual basis in 1952, but catches
remained low through 1957, ranging from only 24 to
158 mt per year (Table 60-4). Effort increased
substantially in subsequent years with catches peak-
ing at 4,400 mt in 1962 and 4,900 mt in 1963. After
that year, catches declined steadily to 173 mt in
1973, and since then have amounted to less than 500
mt per year. Reduced catches resulted from a decline
in abundance of Pacific halibut and restrictions
placed on the fishery because of this decline. Factors
that may have contributed to the decline in abun-
dance (Hoag 1976) included (1) overfishing by the
North American and Japanese setline fisheries in the
early 1960's, (2) high incidental catches of juveniles
in foreign trawl fisheries, and (3) adverse environ-
mental conditions.
FOREIGN FISHERIES
Five foreign countries (besides Canada) have
participated in the groundfish fisheries of the eastern
Bering Sea and Aleutian Islands. Japan, with the
longest history of fishing in the region, has mounted
the greatest effort over the years. The first docu-
mented fishery for demersal species by the Japanese
in the eastern Bering Sea was an exploratory effort
in 1930. This was followed by a relatively small
fishery in 1933-37 and 1940-41 and, starting in 1954,
by the larger modern-day fishery. Except for Canada,
the U.S.S.R. was the second foreign nation to send
demersal fishing fleets to the eastern Bering Sea
(in 1958); this fishery is the second largest for ground-
fish in the region. The Japanese and Soviet fleets
were followed by those of the Republic of Korea
(R.O.K.) in 1967. The number of vessels and magni-
tude of the R.O.K. catches have remained much
smaller than those of Japan and the U.S.S.R. The
Taiwanese have also had a fishery in the eastern
Bering Sea since late 1974 but it involves only one or
two trawlers. Polish vessels fished briefly in the
eastern Bering Sea in 1973 (Law Enforcement Divi-
sion 1975). After 1973, Poland agreed to abstain
from further fishing in the eastern Bering Sea but was
allowed to fish in certain waters of the Aleutian
Islands. Poland did not pursue this fishery, however.'
Japanese fishery
After the initial exploratory effort by two trawlers
in 1930, the Japanese returned to the eastern Bering
Sea with a mothership/catcher boat operation in
' In 1980, Poland resumed and West Germany initiated fishing
operations for groundfish in the eastern Bering Sea under the
U.S. Fishery Conservation and Management Act (renamed
the Magnuson Fishery Conservation and Management Act).
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Demersal fish 1019
TABLE 60-3
Estimated catches of Pacific cod in the eastern Bering Sea,
1864, 1882-1950 (Pereyra et al. 1976^).
Year
1864
1882
1883
1884
1885
1886
1887
1888
1889
1890
1891
1892
1893
1894
1895
1896
1897
1898
1899
1900
1901
1902
1903
1904
1905
1906
1907
1908
1909
1910
1911
1912
1913
1914
Number
of
vessels
7
12
10
11
16
11
9
11
12
9
10
9
9
13
Estimated
catch
(mt)
Year
Number
of
vessels
23
673
1,944
1,867
1,510
1,219
944
1,500
0
245
2,102
3,316
1,658
2,699
2,638
3,633
4,337
1,745
3,995
4,168
4,015
6,270
6,116
6,400
8,654
7,758
6,216
7,643
8,511
6,589
7,867
5,485
6,180
9,817
1915
1916
1917
1918
1919
1920
1921
1922
1923
1924
1925
1926
1927
1928
1929
1930
1931
1932
1933
1934
1935
1936
1937
1938
1939
1940
1941
1942
1943
1944
1945
1946
1947
1948
1949
1950
13
13
16
17
17
24
6
10
17
15
14
7
7
8
9
4
5
5
7
5
5
4
3
3
4
3
1
0
1
1
2
2
1
1
1
Estimated''
catch
(mt)
12,016
13,947
13,946
12,719
12,140
8,576
3,102
5,923
8,951
9,889
10,489
9,924
6,887
7,083
7,851
7,674
4,314
4,692
5,779
6,361
5,713
5,008
4,885
3,963
3,960
4,129
2,940
814
0
656
639
997
1,041
1,006
850
668
^Original catch data in numbers of fish for 1864, 1882-1925
from Cobb (1927) and weight of cured products for 1926-50
from Bower (1927-53) are converted to round weight in
metric tons from conversion factors provided by Cobb (1927).
^Catches for 1916-25 also include offshore catches from the
North Pacific Ocean.
1933 (Forrester et al. 1978). This fishery was directed
toward walleye pollock and flounders off Bristol
Bay, which were processed into fish meal. It ceased
in 1937 because of a decline in the price of fish meal.
Annual catches of pollock and other species during
this five-year period ranged from 3,300 to 43,400
mt.
In 1940-41, the Japanese returned to the east-
em Bering Sea with another mothership opera-
tion, this time for yellowfin sole. The catches of
TABLE 60-4
Catch of Pacific halibut by Canadian and U.S. vessels in the
eastern Bering Sea (North Pacific Fishery Management
Council 1979).
Year
1930
1931
1933
1945
1952
1953
1954
1955
1956
1957
1958
1959
1960
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975
1976
1977^
Canada
0
0
0
0
0
0
0
0
51
0
731
1,442
2,016
1,163
2,113
2,886
758
356
385
668
402
404
536
440
149
58
101
102
37
84
Catch (mt)
U.S.
62
62
11
3
152
137
24
27
107
24
582
1,065
1,392
1,231
2,304
2,022
647
449
336
776
395
340
148
83
293
115
162
215
278
366
Total
62
62
11
3
152
137
24
27
158
24
1,313
2,507
3,408
2,394
4,417
4,908
1,605
805
721
1,444
797
744
684
523
442
173
263
317
315
450
'Preliminary
1020 Fisheries biology
about 10,000 mt each year were frozen for human
consumption.
With the signing of the peace treaty between the
U.S. and Japan in 1952, restrictions on Japanese
distant- water fisheries were removed, and fishing
in the eastern Bering Sea was resumed in 1954. The
Japanese postwar fishery for groundfish in the
Bering Sea developed into four principal components:
the mothership fishery, the North Pacific trawl
fishery, the North Pacific longline-gillnet fishery,
and the landbased trawl fishery. These fisheries
contributed 64, 31, 0.3, and 5 percent, respectively,
to the total Japanese catch in the Bering Sea in the
period 1971-76 (Sasaki 1977).
The mothership fishery has been further catego-
rized into freezing fleets, meal and minced-fish fleets,
and longline-gillnet fleets (Forrester et al. 1978). The
freezing fleets at first exploited yellowfin sole, but
beginning in the early 1960 's expanded to other
species such as Pacific halibut, sablefish, herring, and
Pacific ocean perch. The meal and minced-fish fleets
first produced meal from yellowfin sole and Green-
land turbot, but since the mid-1 960 's have been
producing minced fish (surimi) from pollock.
Catcher vessels used to supply these large (5,000-
14,000 tons) motherships of the freezing and meal
and minced-fish fleets have been stern trawlers, pair
trawlers, side trawlers, and Danish seiners. The
longline-gillnet fleets composed of small 200-2,500-
ton motherships, accompanied by gillnetters and
longliners, have taken halibut, cod, sablefish, and
herring for freezing. The mothership fleets, which
may remain at sea as long as six months, are supplied
by transport vessels which also carry products from
the motherships back to Japan.
The North Pacific trawl fishery is conducted by
large independent trawlers that both fish and process
their catch. In the beginning, catches were frozen,
but since 1968 the number of large trawlers (> 3,000
tons) with processing plants for producing meal and
minced fish has increased (Forrester et al. 1978).
Pollock has been the main target species since the
late 1960's. Transport vessels also supply this fishery
and carry products back to Japan.
The North Pacific longline-gillnet fishery consists
of longline-gillnetters that operate independently of
motherships and process their own catch. These
vessels are not supported by transport vessels and
return to Japan when their holds are full. Sable-
fish and Pacific herring have been primary target
species of this fishery.
Vessels of the landbased trawl fishery also operate
independently; since they are prohibited by Japanese
regulation from transshipping their catch to transport
vessels, they must return to home ports when they
are filled. Danish seiners and stern trawlers of 100-
350 tons have operated in the landbased fishery, but
Danish seiners have been phased out. Catches are
chiefly flounders. Pacific ocean perch, and sablefish.
This fishery is restricted by Japanese regulation to
waters west of 170°W and north of 48°N.
The postwar history of the Japanese fishery can
be divided into three time periods (1954-57, 1958-63,
and from 1964 to the present) on the basis of target
species, methods of processing catches, and expan-
sion of fishing grounds (after Forrester et al. 1978).
In the first period (1954-57) the fishery was rela-
tively small, involving two to four mothership fleets
and one to three independent trawlers of the North
Pacific trawl fishery. Fishing was off Bristol Bay for
flounders, primarily yellowfin sole, for freezing.
In the second period (1958-63), the Japanese
fisheries expanded throughout the Bering Sea with a
variety of fishing and processing methods and target
species (Forrester et al. 1978). The mothership
fleets and independent trawlers extended their
operations to include (for freezing) sablefish. Pacific
ocean perch, and other species and expanded the area
fished to include Aleutian Island waters and the outer
continental shelf and slope in the central and north-
ern Bering Sea. The landbased trawl fishery also
began operations in this period.
The major fishery during the 1958-63 period
continued to be for yellowfin sole on the eastern
Bering Sea continental shelf (Fig. 60-2). Although
the Japanese continued to take yellowfin sole and
other flounders for freezing, they began to use these
species for fish meal in 1958. Catches by the Japan-
ese freezing and fish-meal fleets and by Soviet trawl-
ers (which also began targeting on yellowfin sole in
Figure 60-2. Catch of yellowfin sole being unloaded on
the deck of a Japanese mothership.
Demersal fish 1021
I
►
1958) rose rapidly in this period and reached their
peak in 1960-62, ranging between 421,000 and
554,000 mt annually.
The third period of the Japanese fishery (1964 to
the present) is primarily characterized by the develop-
ment of the pollock fishery (Fig. 60-3). With a
decline in abundance of yellowfin sole (apparently
due to overfishing in the early 1960 's) and the
development in 1964 of techniques for processing
minced fish (surimi) on motherships and large inde-
pendent trawlers, the main Japanese effort shifted to
pollock. Meal and frozen fish became by-products of
the surimi operations. Pollock has dominated Japan-
ese catches since 1963, and from 1970 to 1978
formed over 80 percent of the total Japanese catches
of demersal species in the eastern Bering Sea.
The effort of the Japanese fisheries in the eastern
Bering Sea has generally increased since 1964 and has
remained at a high level through 1978 (Table 60-5).
Although some types of gear have been phased out
of the fisheries (side trawls in 1973 and gillnets in
1978), and the effort by pair trawls and Danish seines
has declined in the 1970's, increases in effort by
stern trawlers in the mothership. North Pacific and
landbased trawl fisheries, and longline vessels have
probably compensated for these declines. Effort by
landbased trawlers in the eastern Bering Sea increased
sharply in 1977 (Table 60-5). This increase stemmed
from restrictions placed on Japanese trawlers in the
Soviet 200-mile fishery zone. Effort by stern trawl-
ers in the mothership and North Pacific trawl fisheries
and by longliners in the North Pacific longline-gillnet
fishery reached a peak in 1978.
Although most of the effort by Japan in the
eastern Bering Sea is for pollock, target fisheries
have continued for such species as yellowfin sole.
Figure 60-3. Large catch of pollock taken by a Japanese
independent stern trawler.
Greenland turbot, and sablefish, and occasionally
for Pacific cod and Pacific ocean perch.
Soviet fishery
Like the Japanese groundfish operations, the
Soviet distant-water fishery also employs both
catcher boats that deliver their catches to factory
ships or to processing and freezing transport vessels
and larger trawlers that process their own catches.
The U.S.S.R. has perhaps utilized the fleet concept of
fishing operations to a greater extent than any other
nation (Pruter 1976). To enable the fishing vessels
to operate at sea for long periods, they are closely
supported by numerous other vessels, including base
ships that carry fleet administrators and staff and
provide logistic support; factory ships for processing
catches; refrigerator transports to replenish stores
and to receive, freeze, and transport catches to home
ports; oil tankers, passenger ships, tugs, patrol vessels,
and, occasionally, even hospital ships. Refrigerated
transports are the mainstay of the support operations.
The basic features of the Soviet fishing vessels are
summarized in Table 60-6.
The first commercial operation by the U.S.S.R.
off Alaska, after exploratory work in 1957-58, was a
fishery for flounders in the eastern Bering Sea begun
in 1958. Like the Japanese, the Soviets have expanded
their fisheries in effort, target species, and fishing
areas. They have carried out three major groundfish
fisheries in the eastern Bering Sea and Aleutian
Islands: a flounder fishery in the southeastern
Bering Sea, a rockfish fishery primarily in the Aleut-
ian Islands, and a pollock fishery along the outer
continental shelf and slope from immediately north
of the eastern Aleutian Islands to northwest of the
Pribilof Islands (Chitwood 1969; Forrester et al.
1978; Haskell 1964; Office of Enforcement and
Surveillance 1965, 1967-70; Enforcement and Sur-
veillance Division 1971, 1973; Law Enforcement
Division 1974, 1975, 1977).
The Soviet flounder fishery was a winter operation
throughout most of its history, extending usually
from November to April with effort peaking in
February or March. The primary target species was
yellowfin sole for freezing in the round or for meal.
Catches of yellowfin sole reached a peak in the
early years of the fishery, increasing from an esti-
mated 5,000 mt in 1958 to about 154,000 mt in
1961 and 140,000 mt in 1962. Although the effort
of the Soviet flounder fishery increased later to a
maximum (involving 70-100 trawlers during peak
months) in the period 1966-68, catches never re-
gained the levels of 1961 and 1962. The Soviet
effort for flounders generally declined after 1968,
TABLE 60-5
Effort by gear type in the eastern Bering Sea (east of 180°) by Japanese fisheries, 1964-78.
Mothership, North Pacific trawl, and North Pacific
Landbased dragnet
longline
-gillnet fisheries
fishery
Stern
Pair
Side
Stern
trawl
trawl
Danish
trawl
trawl
(hrs
(hrs
seine
Longline
Gillnet
(hrs
(hrs
Year
trawled)
trawled)
(no. sets)
(no. hachi)*
(no. tans)^
trawled)
trawled)
1964
402
11,799
59,715
19,317
0
34,501
0
1965
1,275
6,960
47,422
1,989
0
9,568
8,562
1966
4,062
11,800
43,739
6,154
0
26,698
10,906
1967
19,185
20,626
66,798
7,792
12
30,413
16,100
1968
58,682
15,242
66,558
1,580
3,174
9,260
32,564
1969
66,427
13,889
69,834
2,908
5,109
10,046
36,740
1970
72,226
31,262
79,795
5,337
8,383
4,796
48,665
1971
103,164
42,868
61,835
10,005
13,436
2,418
60,347
1972
98,578
46,244
51,382
8,246
12,217
1,333
63,095
1973
95,695
46,810
47,311
8,483
13,092
0
36,482
1974
106,928
46,783
32,131
5,945
9,594
0
62,399
1975
114,999
42,337
22,897
11,768
4,576
0
69,486
1976
109,705
39,651
20,110
15,138
12,819
0
79,985
1977
104,399
35,727
16,055
18,818
5,333
0
143,017
1978
127,370
32,254
17,421
36,031
0
0
133,618
^Hachi is the Japanese unit of longline gear; hachi may range from 58 to 100 m in length.
•^Tan is the Japanese unit of gillnet 50 m long and 5 m deep.
TABLE 60-6
Basic types of fishing vessels employed by the U.S.S.R. in groundfish fisheries off Alaska (Pruter 1976)
Vessel
type
Gross
tons
Length
(m)
Number in
crew
Description
SRT
SRTR
265-335
505-630
38
52
22-26
26-28
Small side trawler of older type
Medium side trawlei^usually transships
catch to factory ship but may operate
independently and process and freeze
own catch
SRTM
700
54
30
Large side trawler— frequently operates
independently of factory ships and proc-
esses and freezes own catch
SRTK
BMRT
775
3,170
85
90
New class of trawler equipped with stern
ramp for more efficient trawling
Factory trawler which normally proc-
esses and freezes own catch
RTM
2,657
82
Newer type of factory trawler with in-
creased deck area aft for more efficient
handling of gear and catch
1022
Demersal fish 1023
presumably because of reduced abundance of yellow-
fin sole. The Soviet flounder fishery, discontinued in
1973, was not resumed until 1978, after the resource
recovered (Bakkala et al. 1979).
The Soviet fishery for Pacific ocean perch and
other rockfish began in 1960, when 25-30 trawlers
fished along the edge of the continental shelf in the
eastern and central Bering Sea. Beginning in 1963,
effort for Pacific ocean perch became centered in
Aleutian Island waters and the Gulf of Alaska;
since then catches in the eastern Bering Sea have rep-
resented only a by-catch of the pollock fishery.
Soviet trawlers caught a maximum of 34,000 mt of
Pacific ocean perch and other rockfish in the eastern
Bering Sea in 1961. Rockfish have been processed by
freezing in the round, headed and gutted, or as fillets.
The fishery that eventually developed into the
pollock fishery began in 1967, targeting at first on
sablefish and large flounders (arrowtooth flounder
and Greenland turbot) on the outer continental
shelf and slope of the southeastern Bering Sea. This
fishery gradually expanded northward along the
edge of the continental shelf and by 1969 had be-
come a year-round operation, taking on the general
appearance that has characterized it to the present
time. Two principal fishing areas were used, one
immediately north of the eastern Aleutian Islands and
the other northwest of the Pribilof Islands. Effort
normally peaked in late winter, when fishing vessels
from the Pacific herring and flounder fisheries joined
the pollock fleet.
The emphasis of this fishery shifted to walleye
pollock in the early 1970's, with catches rising from
about 36,000 mt in 1970 to 234,000 mt in 1971.
Pollock has remained the predominant target species
of the Soviet fishery. The peak catch of pollock
occurred in 1974, when almost 310,000 mt was
taken. Products from pollock have been fish frozen
whole or headed and gutted, fillets, and fish meal.
Republic of Korea and Taiwanese fisheries
Fisheries by the Republic of Korea (R.O.K.) in
the eastern Bering Sea have been on a much smaller
scale than those of Japan and the U.S.S.R. (Office
of Enforcement and Surveillance 1968, 1969, and
1970; Enforcement and Surveillance Division 1971
and 1973; Law Enforcement Division 1974, 1975,
and 1977). After exploratory fishing in 1966, the
R.O.K. began a relatively small-scale commercial
operation in the eastern Bering Sea in 1977. The
fleet was enlarged in subsequent years to include
factory ships, accompanied by independent stern
trawlers, some of which exceeded 5,000 tons, pair
trawlers, and eventually longliners and Danish seiners.
The principal target species has been pollock. Until
1972, fishing was limited to spring and summer
months, but by 1973 the fishery was a year-round
operation. Estimates by U.S. surveillance of the
R.O.K. fishery indicated that pollock catches ranged
between 1,200 and 26,000 mt annually from 1968
to 1975. The annual pollock catch reported by the
Koreans for 1976-78 has ranged from about 40,000
mt to 85,000 mt.
The Taiwanese fishery, which began in December
1974, has employed only one or two independent
stern trawlers. The trawlers have fished in winter
and spring months along the continental shelf edge
west and southwest of the Pribilof Islands, targeting
on pollock and flounders. The total catch in 1977
was 1,500 mt, of which 90 percent was pollock.
Magnitude of catches
Total foreign catches of demersal species from the
eastern Bering Sea during the history of the modern
fishery (1954-78) are illustrated in Fig. 60-4; catch
statistics by species and nation are given in Table
60-7. Catches have reached two peaks since 1954;
the first and smaller peak occurred in 1960-62,
1500 -
1000 -
1978
1958
1978
Years
Figure 60-4. Foreign catches in metric tons (mt) of
groundfish in the eastern Bering Sea (east of long. 180°)
by nation (upper panel) and by species group (lower panel),
1954-78.
TABLE 60-7
Foreign catches of groundfish in the eastern Bering Sea (east of 180°) 1954-78.
(0 indicates no fishing, — indicates fishing, but no reported catch.)
Species
Nation
1954
1955
L956
1957
1958
1959
1960
1961
1962
1963
1964
1965
Pollock
Japan
_
_
_
_
6
924
32
793
26,097
24,216
58,765
103,353
171,957
229,275
USSR
0
0
0
0
-
-
-
-
-
-
-
-
ROK^'
0
0
0
0
0
0
0
0
0
0
0
0
Others-
0
0
0
0
0
0
0
0
0
0
0
0
Total
-
-
-
-
6
924
32
793
26,097
24,216
58,765
103, 353
171,957
229,275
Pacific cod
Japan
-
-
-
-
171
2
864
5,679
2,448
6,054
3,879
13,408
14,722
USSR
0
0
0
0
-
-
-
-
-
-
-
-
ROK
0
0
0
0
0
0
0
0
0
0
0
0
Others
0
0
0
0
0
0
0
0
0
0
0
0
Total
-
-
-
-
171
2
864
5,679
2,448
6,054
3,879
13,408
14,722
Pacific ocean
Japan
-
-
-
-
-
-
1,100
13,000
12,900
17,500
13, 588
8,723
perch and
USSR
0
0
0
0
-
-
5,000
34,000
7,000
7,000
7,000
9,000
other rockfish
ROK
0
0
0
0
0
0
0
0
0
0
0
0
Others
0
0
0
0
0
0
0
0
0
0
0
0
Total
-
-
-
-
-
-
6,100
47,000
19,900
24,500
20,588
17,723
Sablefish
Japan
-
-
-
-
32
393
1,861
26,183
28,521
18,404
6,165
5,001
USSR
0
0
0
0
-
-
-
-
-
-
-
-
ROK
0
0
0
0
0
0
0
0
0
0
0
0
Others
0
0
0
0
0
0
0
0
0
0
0
0
Total
-
-
-
-
32
393
1,861
26,183
28,521
18,404
6,165
5,001
Yellowfin sole
Japan
12,562
14
,690
24
697
24
145
39
153
123
121
360,103
399,542
281,103
20,504
48,880
26,039
USSR
0
0
0
0
5
000
62
200
96,000
154,200
139,600
65,306
62,297
27,771
ROK
0
0
0
0
0
0
0
0
0
0
0
0
Others
0
0
0
0
0
0
0
0
0
0
0
0
Total
12,562
14
690
24
697
24
145
44
153
185
321
456,103
553,742
420,703
85,810
111,177
53,810
Rock sole
Japan
-
-
-
-
-
-
_
-
-
1,196
1,432
1,780
USSR
0
0
0
0
-
-
-
-
-
3,806
1,806
1,898
ROK
0
0
0
0
0
0
0
0
0
0
0
0
Others
0
0
0
0
0
0
0
0
0
0
0
0
Total
-
-
-
-
-
-
-
-
-
5,002
3,238
3,678
Flathead sole
Japan
-
-
-
-
-
-
_
_
_
7,079
11,121
3,287
USSR
0
0
0
0
-
-
-
-
-
22,546
14,167
3,426
ROK
0
0
0
0
0
0
0
0
0
0
0
0
Others
0
0
0
0
0
0
0
0
0
0
0
0
Total
-
-
-
-
-
-
-
-
-
29,625
25,288
6,713
Alaska plaice
Japan
_
_
-
-
-
-
_
_
_
233
808
474
USSR
0
0
0
0
-
-
-
-
-
742
1,030
505
ROK
0
0
0
0
0
0
0
0
0
0
0
0
Others
0
0
0
0
0
0
0
0
0
0
0
0
Total
-
-
-
-
-
-
-
-
-
975
1,838
979
Pacific halibut
Japan
_
-
-
-
196
674
6,931
3,480
7,865
7,452
1,271
1,369
USSR
0
0
0
0
-
-
-
-
-
-
-
-
ROK
0
0
0
0
0
0
0
0
0
0
0
0
Others
0
0
0
0
0
0
0
0
0
0
0
0
Total
-
-
-
-
196
674
6,931
3,480
7,865
7,452
1,271
1,369
Arrowtooth
Japan
flounder
USSR
ROK
Catche
5 of
arrowtooth
flounder
and Greenland turbot
Others
c
Dmbin
ed until 1970.
Total
Greenland
Japan
_
_
_
-
_
_
36,843
57,348
58,226
31,565
33,729
7,947
turbot
USSR
0
0
0
0
-
-
-
-
-
-
-
1,800
ROK
0
0
0
0
0
0
0
0
0
0
0
0
Others
0
0
0
0
0
0
0
0
0
0
0
0
Total
-
-
-
-
-
-
36,843
57,348
58,226
31,565
33,729
9,747
Other groundfish
Japan
-
-
-
-
147
380
10,260
554
5,931
1,102
736
2,218
USSR
0
0
0
0
-
-
-
-
-
-
-
-
ROK
0
0
0
0
0
0
0
0
0
0
0
0
Others
0
0
0
0
0
0
0
0
0
0
0
0
Total
-
-
-
-
147
380
10,260
554
5,931
1,102
736
2,218
All groundfish
Japan
12,562
14
690
24
697
24
145
46
623
160
225
448,874
526,771
459, 365
212,267
303,095
300,835
total
USSR
0
0
0
0
5
000
62
200
101,000
188,200
146,600
99,400
86,300
44,400
ROK
0
0
0
0
0
0
0
0
0
0
0
0
Others
0
0
0
0
0
0
0
0
0
0
0
0
All-nation total
12,562
14
,690
24
697
24
145
51
623
222
425
549,874
714,971
605,965
311,667
389,395
345,235
^Catch statistics up to 1963 from Forrester et al. 1974, and for 1964-78 from data on file, Northwest and Alaska Fisheries
Center, Seattle, with the following exceptions: Pacific ocean perch and other rockfish— Japanese catches 1960-63 and USSR
catches 1960-66 from Chikuni 1975; blackcod— Japanese catches 1958-63 from Sasaki 1976; and all flounders except halibut-
all nation catches, 1954-76 from Wakabayashi and Bakkala 1978.
^ROK - Republic of Korea.
1024
Demersal fish 1025
I
TABLE 60-7, cont.
I
Nation
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975
1976
1977
1978
Japan
261,694
550,152
701,124
830,525
1,231,347
1,514,030
1,616,532
1,471,189
1,250,654
1,065,078
986,696
774,450
783,048
USSR
-
-
-
33,571
35,590
233,511
213,895
280,005
309,613
216,567
175,539
63,382
91,647
ROK
0
0
1,200
5,000
5,000
10,000
9,200
3,100
26,000
3,438
84,987
39,895
59,570
Others
0
0
0
0
0
0
0
0
-
-
-
1,334
3,057
Total
261,694
550,152
702, 324
869,096
1,271,937
1,757, 541
1,839,627
1,754,294
1,586,267
1,285,083 1
,247,222
879,061
967,322
Japan
18,200
31,982
57,915
50,487
70,078
40,555
35,877
40,817
45,915
33,322
32,009
33,141
41,234
USSR
-
-
-
-
-
2,486
7,028
12,569
16,547
18,229
17,756
177
419
ROK
0
0
-
-
-
-
-
-
-
-
716
-
859
Others
0
0
0
0
0
0
0
0
-
-
-
2
62
Total
18,200
31,982
57,915
50,487
70,078
43,041
42,905
53,386
62,462
51,551
50,481
33, 320
42,574
Japan
16,786
20, 598
26,214
16,150
10, 392
10,369
5,837
3,147
6,811
3,716
3,300
7,771
4,291
USSR
9,000
-
3,087
-
-
-
150
475
31,877
16,465
12,124
90
5
ROK
0
0
-
-
-
-
-
-
-
-
578
478
560
Others
0
0
0
0
0
0
0
0
-
-
-
0
3
Total
25,786
20,598
29,301
16,150
10, 392
10, 369
5,987
3,622
38,688
20,181
16,002
8, 339
4,859
Japan
9,502
10,330
10,143
14,454
8,897
12,304
10,643
4,769
4,189
2,776
2,815
2,801
909
USSR
-
1,237
4,256
1,579
2,874
2,830
2,137
1,192
77
38
29
0
0
ROK
0
0
-
-
-
-
-
-
-
-
115
9
173
Others
0
0
0
0
0
0
0
0
-
-
-
53
5
Total
9,502
11,567
14,399
16,033
11,771
15,134
12,780
5,961
4,266
2,814
2,959
2,863
1,087
Japan
45,423
60,429
40,834
81,449
59,851
82,179
34,846
75,724
37,947
59,715
52,673
58,190
62,736
USSR
56,930
101,799
43,355
85,685
73,228
78,220
13,010
2,516
4,288
6,060
2,908
283
76,300
ROK
0
0
-
-
-
-
-
-
-
-
655
-
69
Others
0
0
0
0
0
0
0
0
-
-
-
-
1
Total
102,353
162,228
84,189
167,134
133,079
160,399
47,856
78, 240
42,235
65,775
56,236
58,473
139,106
Japan
4,037
1,890
2,633
4,285
9,616
20,159
43,055
22,840
17,311
9,682
8,598
5,025
6,671
USSR
5,067
2,872
2,617
4,955
10,507
20,260
17,769
995
2,664
1,463
1,328
265
354
ROK
0
0
-
-
-
-
-
-
-
-
107
-
13
Others
0
0
0
0
0
0
0
0
-
-
-
-
0
Total
9,104
4,762
5,250
9,240
20,123
40,419
60,824
23,835
19,975
11,145
10,033
5,290
7,038
Japan
4,996
10,621
11,851
9,168
20,088
25,538
9,850
17,190
12,889
4,873
7,379
7,057
13,446
USSR
6,024
12,816
9,724
9,395
21,064
25,486
5,840
951
2,028
6 72
795
531
1,152
ROK
0
0
-
-
-
-
-
-
-
-
90
-
19
Others
0
0
0
0
0
0
0
0
-
-
-
-
1
Total
11,020
23,437
21,575
18,563
41,152
51,024
15,690
18, 141
14,917
5,545
8,264
7,588
14,618
Japan
2,054
1,340
1,223
3,127
1,326
517
171
1,0 82
2,168
2,407
3,519
3,119
4,716
USSR
2,579
2,513
1,396
3,815
2,076
475
119
35
220
207
102
0
4,752
ROK
0
0
-
-
-
-
-
-
-
-
44
-
0
Others
0
0
0
0
0
0
0
0
-
-
-
-
6
Total
4,633
3,853
2,619
6,942
3,402
992
290
1,117
2,388
2,614
3,665
3,119
9,474
Japan
2,199
3,756
2,775
2,764
1,735
4,861
955
644
81
137
88
-
0
USSR
-
-
-
-
-
-
490
296
123
137
58
-
0
ROK
0
0
-
-
-
-
-
-
-
-
-
-
0
Others
0
0
0
0
0
0
0
0
-
-
-
2
4
Total
2,199
3,756
2,775
2,764
1,735
4,861
1,445
94 0
204
2 74
146
2
4
Japan
9,354
11,603
3,823
4,929
2,823
1,241
1,717
8,213
7,475
USSR
3,244
7,189
9,301
4,288
18,650
19,591
16,132
3,294
2,576
ROK
-
-
-
-
-
-
2
-
91
Others
0
0
0
0
-
-
-
-
9
Total
12,598
18,792
13,124
9,217
21,473
20,832
17,851
11,507
10, 151
Japan
10,842
21,230
19,980
19,231
14,715
30,193
49,813
43,354
58,834
52,625
51,677
28,248
40,643
USSR
2,200
2,639
15,252
16,798
4,976
10,271
14,697
11,926
10,820
12,194
8,867
2,039
1,543
ROK
0
0
-
-
-
-
-
-
-
_
425
_
28
Others
0
0
0
0
0
0
0
-
-
-
-
47
Total
13,042
23,869
35,232
36,029
19,691
40,464
64,510
55,280
69,654
64,819
60,969
30,287
42,261
Japan
2,239
4,378
2,984
4,182
9,227
29,617
32, 370
39,911
47,491
42,531
13,527
33,742
47,582
USSR
-
-
19,074
6,277
6,068
3,879
78,523
15,915
12,770
12,314
12,294
624
11,020
ROK
0
0
-
-
-
-
-
-
-
-
322
1,445
2,935
Others
0
0
0
0
0
0
0
0
-
-
-
91
-
Total
2,239
4,378
22,058
10,459
15,295
33,496
110,893
55,826
60,261
54,845
26,143
35,902
61,537
Japan
377,972
716,706
877,676 1
035,822
1,446,626
1,781,925
1,843,772
1,725,596
1,487,113
1,278,103 1
163,998
961,757 1
012,751
USSR
81,800
123,876
98,761
162,075
159,627
384,607
362,959
331,163
409,677
303,937
247,932
70,685
189,768
ROK
0
0
1,200
5,000
5,000
10,000
9,200
3,100
26,000
3,438
88,041
41,827
64,317
Others
0
0
0
0
0
0
0
0
-
-
-
1,482
3,195
459,772
840,582
977,637 1
,202,897
1,611,253
2,176,532
2,215,931
2,059,859
1,922,790
1,585,478 1
499,971 1
,075,751 1
270.031
when Japan and the U.S.S.R. were intensively ex-
ploiting yellowfin sole for fish meal. Total estimated
catches of yellowfin sole and other species reached
715,000 mt in 1961, and then declined because of
reduced abundance of yellowfin sole to between
310,000 and 390,000 mt in 1963-65. After the
Japanese developed shipboard methods of producing
surimi, their fishery for pollock developed rapidly
1026 Fisheries biology
and all-nation catches of demersal species rose again
to reach a second much higher peak of over 2.0
million mt per year in 1971-73. Since then, catches
have declined as a result of restrictions placed on the
fisheries because of evidence that abundance of
pollock and other species had declined. By 1977,
catches were reduced to about 1.1 million mt, but
rose in 1978 to about 1.3 million mt.
Japan has taken most of the catches in the eastern
Bering Sea (Fig. 60-4), accounting for at least 68
percent and usually between 80 and 90 percent of
the total foreign catches annually.
Flounders (primarily yellowfin sole) were the
major species in eastern Bering Sea catches until
1963, after which walleye pollock predominated
(Fig. 60-4). The proportion of pollock in the total
foreign catches increased from about 44 percent in
1964 to about 72 percent in 1968, and from 1971 to
1978 it represented 74-85 percent of the total catch
of demersal species.
The catch composition of the foreign fisheries in
the eastern Bering Sea for the recent period of 1970-
78 is summarized in Table 60-8. Catches of all de-
mersal species have averaged 1,712,700 mt annually
in this period with pollock making up 1,395,000 mt
(81.5 percent) of this total, other roundfish 120,200
mt (7.0 percent), and flounders 197,500 mt (11.5
percent). The largest catches after pollock have been
TABLE 60-8
yellowfin sole, Greenland turbot, and Pacific cod, in
that order.
Although catches of Pacific halibut by North
American fisheries (Table 60-4) and by foreign
fisheries (Table 60-7) have been small, there have
also been incidental catches of halibut in the foreign
trawl and longline fisheries targeting on pollock,
yellowfin sole, and other demersal species in the
Bering Sea. Estimates of incidental catches of Pacific
halibut by these fisheries (Table 60-9) reached a peak
of 11,500 mt in 1971, but have declined since then to
range from 1,166 to 1,853 mt in 1975-78. Foreign
fisheries are prohibited from retaining this species
over much of the eastern Bering Sea, formerly by
international agreements and since 1977 by the
FCMA, but many halibut die from injuries received
during capture (Hoag 1975).
TABLE 60-9
Estimated incidental catches (mt) of Pacific halibut in the
eastern Bering Sea and Aleutian Islands waters by foreign
fisheries targeting on other species (1954-74 estimates from
Hoag and French 1976, 1975-78 estimates from data on file
at the Northwest and Alaska Fisheries Center,
Seattle, Washington).
Japan
Mothership and Land- U.S.S.R.,
independent based R.O.K. and
fleets fleet Taiwan
Year
Total
Average annual foreign catches of demersal fish in the
eastern Bering Sea (east of 180°) in the period 1970-78.
Species or
species group
Average annual Percent of
catch (mt) total
Pollock 1,395,033 81.5
Other roundfish 120,223 7.0
Pacific cod 49,971 2.9
Miscellaneous roundfish 50,466 2.9
Pacific ocean perch and
other rockfish 13,160 0.8
Sablefish 6,626 0.4
Flounders 197,455 11.5
Yellowfin sole 86,822 5.1
Greenland turbot 49,765 2.9
Rock sole 22,076 1.3
Flathead sole 19,659 1.1
Arrowtooth flounder 15,060 0.9
Alaska plaice 3,006 0.2
Pacific halibut 1,067 0.1
All demersal species 1,712,711 100.0
1954
1955
1956
1957
1958
1959
1960
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975
1976
1977
1978
52
42
102
102
168
520
1,590
2,303
1,420
125
412
440
693
1,341
1,765
2,176
2,759
3,484
3,259
2,567
1,807
664
692
387
833
112
659
1,278
1,386
2,533
5,301
3,582
3,594
5,677
5,728
3,678
2,489
1,581
386
205
910
1,781
374
576
926
837
555
476
540
600
738
592
972
957
2,307
2,178
1,987
2,458
116
314
28
239
52
42
102
102
168
894
2,166
3,229
2,369
1,339
2,166
2,366
3,826
7,380
5,939
6,742
9,393
11,519
9,115
7,043
5,846
1,166
1,211
1,325
2,853
Demersal fish 1027
Areas of fishing
Current fishing areas for major species of demersal
fish are illustrated in Figs. 60-5 to 60-11, using Japa-
nese commercial catch statistics from 1977. Principal
areas of fishing for pollock and Pacific cod (Figs.
60-5, 60-6) are along the outer continental shelf and
slope in the eastern Bering Sea. The largest catches
of pollock were made between the eastern Aleutian
Islands and the Pribilof Islands and southwest of St.
Matthew Island. From 1973 to 1977, 38 percent of
the pollock catch, representing about 510,000 mt
annually, came from the southeast Bering Sea; almost
all the rest came from north and northwest of the
Pribilofs. Catches of Pacific cod were concentrated
in the same area as those of pollock. Cod are mainly
a by-catch of the pollock fishery, although they are
an occasional target species when high concentrations
Figure 60-5. Distribution of Japanese catches of pollock
in 1977.
165 170 175 180
are detected during pollock fishing operations. They
have also been an occasional target species of the
Japanese longline fishery.
Since Pacific ocean perch and sablefish are dis-
tributed primarily over the continental slope, the
largest catches occurred near the shelf edge (Figs.
60-7, 60-8). Historically, catches of Pacific ocean
perch have been higher in the Aleutian Islands region
than in the eastern Bering Sea, as in 1977 (Fig. 60-7).
Sablefish are more abundant in the eastern Bering
Sea than in the Aleutians.
A third species group taken mainly on the outer
continental shelf and slope of the eastern Bering Sea
is Greenland turbot and arrov^rtooth flounder. As
adults, these large flounders mainly occupy conti-
nental slope waters, whereas juveniles are generally
found on the shelf. Major concentrations of adults
"•\_* ..• ^-jjt-^' i^^is
Figure 60-6. Distribution of Japanese catches of Pacific
cod in 1977.
Figure 60-7. Distribution of Japanese catches of Pacific
ocean perch in 1977.
Figure 60-8. Distribution of Japanese catches of sable-
fish in 1977.
1028 Fisheries biology
are found at depths of 200-700 m in summer and
300-900 m in winter (Shuntov 1970). The largest
catches of Greenland turbot and arrowtooth flounder
by Japanese fisheries in 1977 were made near the
shelf edge; most of the total catch came from north-
west of the Pribilof Islands (Fig. 60-9).
GREENLAND TURBOT AND
ARROWTOOTH FLOUNDER
E3<,00m,
Ea, 00. 000 m,
Figure 60-9. Distribution of Japanese catches of Green-
land turbot and arrowtooth flounder in 1977.
The small flounders, mainly yellowfin sole, rock
sole, flathead sole, and Alaska plaice, are mainly
confined to the continental shelf. These species,
except for flathead sole, perform extensive migra-
tions, onshore in spring and offshore in fall. Con-
centrations of these species, as catch statistics show,
depend on the seasonal timing of the fishery. In
1977 the target fishery for yellowfin sole was in
January-February and September-December. In
these periods, the largest catches of yellowfin sole
were taken east of the Pribilof Islands (Fig. 60-10).
Catches of other small flounders consist mainly of
rock sole and flathead sole, but include a number of
other species such as Alaska plaice, starry flounder,
longhead dab, and rex sole. These species are taken
incidentally in the pollock and yellowfin sole fisher-
ies. Concentrations of these species in Japanese
catches in 1977 were widely distributed from depths
of less than 100 m off Bristol Bay to near the shelf
edge northwest of the Pribilof Islands (Fig. 60-11).
Catches in shallower regions of the southeast Bering
Sea were principally rock sole and Alaska plaice,
and those in deeper waters of the southeast Bering
Sea and northwest of the Pribilof Islands were princi-
pally flathead sole and rock sole.
■^^-^-^
Figure 60-10. Distribution of Japanese catches of yellow-
fin sole in 1977.
Figure 60-11. Distribution of Japanese catches of "other
flounders" in 1977.
Apparent effect of the fisheries on the resources
Foreign fisheries may have reduced the demersal
fishery resources of the eastern Bering Sea consider-
ably. Substantial reductions in abundance of most of
the target species have been observed; some of these
have undoubtedly been the direct result of high
exploitation rates. The declines in abundance of
yellowfin sole and Pacific halibut in early stages of
the commercial fishery and in Pacific ocean perch,
sablefish, and pollock in later stages have probably
resulted, wholly or partly, from overexploitation.
Other commercial species which are primarily taken
as a by-catch of the pollock and yellowfin sole
fisheries have shown little evidence of substantial
reductions in abundance. However, assessment data
for these nontarget species from commercial opera-
tions and research vessel surveys have not been as
good as those for target species.
Sharp declines in relative abundance (catch-per-
unit-effort, CPUE) in the commercial fishery for
pollock during the period 1972-75 suggest that
Demersal fish 1 029
catches in 1970-75, ranging from 1.3-1.8 million mt
annually, were not sustainable (Bakkala et al. 1979).
The CPUE for pollock has leveled off since 1976,
perhaps as a result of management measures which
have reduced catches to about 1.0 million mt annu-
ally. The equilibrium yield (EY, see Management
Regime section) in 1979 was estimated to be 1.0
million mt but has now been revised to 1.2 mt.
Intense exploitation by Japanese and Soviet
fisheries in the early 1960's may have reduced the
abundance of yellowfin sole to 40 percent of its
virgin stock size (Wakabayashi et al. 1977). The
stock remained at a relatively low level of abundance
through the 1960's and may have reached its lowest
point in 1969. Beginning in about 1972, the resource
began a recovery which continued at least through
1978. Data from research vessel surveys have indi-
cated that the exploitable biomass (fish older than
five years) may have approxim.ately doubled from
about 643,000 mt in 1973 to about 1,400,000 mt in
1978 (Bakkala et al. 1979). This increase has resulted
from the recruitment of a series of abundant year-
classes originating in 1966-70. The resource has
recovered to a level that will support some increase in
catches.
The stock condition of Pacific cod has been
difficult to assess because this species is usually inci-
dental in commercial catches and, because of its
semidemersal distribution, is only partially available
to bottom trawl gear during research vessel surveys.
The information available indicates that the eastern
Bering Sea stock has been relatively stable (Bakkala
et al. 1979). Evidence from research vessel surveys
has shown that the 1977 and 1978 year-classes of
cod are relatively abundant, and because these year-
classes will form the bulk of the exploitable stock
in 1980 and 1981, the equilibrium yield in these
years is expected to be somewhat higher than the
conservative estimate of maximum sustainable yield
(MSY, see Management Regime section).
Greenland turbot and arrowtooth flounder are
managed as a single unit because of the similarities
of their life histories and distributions. Greenland
turbot, the more valuable commercially, is a target
species of the Japanese landbased trawl fishery.
Catches of this species complex have averaged about
65,000 mt since 1970; Greenland turbot has con-
tributed about 80 percent of the total. Information
about this species complex has been inadequate to
accurately assess potential yields, estimated from
catch data to be about 100,000 mt for the eastern
Bering Sea and Aleutians (North Pacific Fishery
Management Council 1979). However, during the
period 1972-76, when catches of these species in the
eastern Bering Sea and Aleutian Islands area aver-
aged about 90,000 mt, a substantial decline in CPUE
of Greenland turbot occurred in the landbased
trawl fishery. This decline was arrested in 1976-78,
when annual catches averaged about 76,000 mt,
indicating that catches of this magnitude may have
more closely approximated equilibrium yield
(Bakkala et al. 1979).
"Other flounders" is a second species group man-
aged as a single unit. Commercial catches of this
group are mainly rock sole and flathead sole with
lesser amounts of Alaska plaice and trace amounts of
such small flounders as rex sole, starry flounder,
butter sole, longhead dab, and Dover sole. These
species are rarely targeted and are taken mainly as a
by-catch of the pollock and yellowfin sole fisheries.
Good assessment data have been lacking; maximum
sustainable yields for the complex have been esti-
mated from historical catch data and biomass estim-
mates from research vessel surveys. The estimates
from these sources range from 44,300 to 76,800 mt
with a mean value of 61,000 mt. Until recently,
these stocks have appeared healthy. Evidence from
research vessel surveys in 1977, however, indicates
that the 1971-73 year-classes of rock sole and the
1971-72 year-classes of flathead sole, now being
recruited to the exploitable stock, may be weak;
the complex may be entering a period of reduced
abundance (Bakkala et al. 1979).
Stocks of Pacific Ocean perch and sable fish in the
eastern Bering Sea are in poor condition with current
catches and indices of abundance at extremely low
levels. From a peak of 47,000 mt in 1961, catches
of rockfish (predominantly Pacific ocean perch) have
showTi a steady decline to 2,200 mt in 1978 (Bakkala
et al. 1979). Indices of relative abundance in the
Japanese fishery declined sharply from 1968 to 1971
and have remained at a low level since 1971. This
information, combined with the absence of any
evidence of strong year-classes entering the exploit-
able population, indicates that the stock will remain
at a low level of abundance in the near future.
Although sablefish stocks are also currently de-
pleted, the outlook for this resource is encouraging
due to the apparent high abundance of juvenile fish
that will be entering the fishable stock over the next
few years. After commercial catches of from 14,000
to 16,000 mt in 1968 and 1969 in the eastern Bering
Sea, catches decUned steadily to about 1,100 mt in
1978. Indices of abundance from the Japanese long-
line fishery have also showm a substantial decline in
this period (Bakkala et al. 1979). Improvement is
expected in the sablefish resource due to unusually
high abundances of young fish (40-60 cm) observed
1030 Fisheries biology
in 1979 commercial and research-vessel catches
(Bakkala et al. 1979, Sasaki 1979).
The abundance of halibut in the eastern Bering
Sea has also declined sharply. This decline, since
the early 1960's, has been evident from indices of
abundance in the North American setline fishery
(International Pacific Halibut Commission 1977)
and from the commission's research vessel surveys of
juvenile halibut (Best 1977). The stock has appar-
ently stabilized at a lovi^ level since 1970. Catches by
the North American fishery have averaged about
300 mt annually in this period. The abundance of
juvenile halibut increased from 1972 to 1977 (Inter-
national Pacific Halibut Commission 1979), although
it did not reach levels observed in the early 1960 's.
However, because the fishable stock consists of
relatively old fish, this increase will not benefit the
fishery for a number of years. Equilibrium yield has
been estimated to approximate the present level of
catch (300 mt annually), well below the estimated
potential yield of 5,000 mt.
MANAGEMENT REGIME
Regulation of fisheries in Alaskan waters was
initially the responsibility of the Bureau of Commer-
cial Fisheries (predecessor of the National Marine
Fisheries Service) and the International Pacific
Halibut Commission (IPHC). Restrictions imposed
on the domestic fishery by the bureau primarily dealt
with the size, characteristics, and operation of trawls
(North Pacific Fishery Management Council 1979).
In 1959 the State of Alaska assumed responsibility
for regulating domestic fisheries in state waters. It
required all commercial fishermen landing any species
of fish or shellfish to possess a commercial fishing
license and the captains or owners of fishing vessels
to license their vessels and fishing geair. Fish buyers
were required to keep records of each purchase,
including the identity of the vessel landing the
catch, the weight by species and statistical area of the
catch, and the type of gear used. The state issued a
number of other regulations, many of which were
specific to the Gulf of Alaska, where domestic
fisheries have been most active (North Pacific Fishery
Management Council 1979).
The North American halibut fishery in the Bering
Sea was managed at first by the IPHC. Beginning in
1963, management of halibut reverted to the Inter-
national North Pacific Fisheries Commission (INPFC),
whose member nations (Canada, Japan, and the
United States) have relied on the IPHC for scientific
information on the condition of the halibut stocks
and recommendations for regulations to conserve the
resource. Regulatory measures used before and
during the involvement of INPFC in management of
halibut have consisted of season and catch quota
restrictions; minimum size limits, gear restrictions,
and closed areas to reduce the mortaUty of haUbut of
less than optimum size; season and area restrictions to
distribute fishing effort and facilitate enforcement;
licensing of vessels; and the reporting of catch and
effort data by statistical area to provide information
on the condition of stocks (Dunlop et al. 1964, Bell
1967, Skud 1977).
Regulatory measures affecting foreign fisheries
have come into force through domestic laws and
international agreements and finally (in 1977)
through the FCMA. One of the first international
agreements resulting from the formation of INPFC
was that, starting in 1958, Japan agreed to abstain
from fishing halibut in certain regions of the eastern
Bering Sea provided the stocks met qualifications for
abstention; e.g., that they were substantially ex-
ploited by two or more of the contracting parties
(Forrester et al. 1978). In 1962, member nations of
INPFC agreed that Pacific halibut east of 175°W
in the Bering Sea no longer qualified for abstention.
However, after combined domestic and foreign
catches of about 12,000 mt annually in 1962 and
1963, catches dropped sharply to less than 3,000 mt
in 1964, and Japan ended its target fishery for hali-
but east of 175° W.
In May 1964, U.S. Public Law 88-308 was enacted,
making it unlawful for foreign vessels to fish within
the three-mile limit of territorial waters of the United
States or to fish for designated fishery resources on
the adjacent U.S. continental shelf. In October
1966, U.S. Public Law 89-658 established a nine-
mile contiguous fishery zone adjacent to the three-
mile territorial sea and provided that the United
States would have the same jurisdiction over fisheries
within this zone as it had within its three-mile terri-
torial waters, except that traditional foreign fisheries
could continue to operate in the contiguous zone.
In 1964, the United States initiated bilateral
agreements with Japan and the U.S.S.R. to allow
continuation of traditional foreign fisheries within
the contiguous zone in certain Alaska waters (Office
of Enforcement and Surveillance 1968). One provi-
sion of the 1964 agreement established a king crab
pot sanctuary on the north side of Unimak Island
and the Alaska Peninsula (Fig. 60-12). Trawling was
prohibited the year round in this sanctuary to prevent
conflicts between foreign and domestic gear. The
sanctuary has also served to protect juvenile halibut
and has been retained as part of the FCMA. Also
retained in the FCMA is the "winter halibut savings
area" (Fig. 60-12), which also originated through
J
I
WInUr Halibut
Savings Areas
Figure 60-12. Locations of "winter halibut savings areas"
and the "Bristol Bay pot sanctuary" (North Pacific Fishery
Management Council 1979).
Demersal fish 1031
bilateral agreements. This closure is designed to
reduce the incidental catch of halibut by trawl
fisheries in December-May, when halibut are concen-
trated in this region.
Bilateral agreements with Japan and the U.S.S.R.
were renegotiated at two-year intervals, creating some
changes in areas of fishing and providing loading
zones for transshipping fishery products and supplies
between fishing and cargo vessels within the contig-
uous fishing zone. Bilateral agreements were also
established with Canada in 1970, the Republic of
Korea in 1972, and Poland in 1975.
In 1973, the bilateral agreement with Japan and
the U.S.S.R. began to include catch quotas for
herring and various demersal species of fish in the
eastern Bering Sea and Aleutian Islands region. These
quotas were periodically updated and remained in
force through 1976 (Table 60-10).
TABLE 60-10
Catch quotas (mt) negotiated through bilateral agreements for Japanese and Soviet fisheries in the eastern
Bering Sea and Aleutian Islands region, 1973-76 (North Pacific Fishery Management Council 1979).
Nation
Area
Fishery
Species
1973
Quotas (mt)
1974
1975-76
Japan
Eastern Bering Sea
Aleutians
»
U.S.S.R. Eastern Bering Sea
Aleutians
Mothership and North
Pacific trawl
Pollock
Demersal species
other than pollock
Herring
North Pacific
Herring
longline-gillnet
Landbased trawl
All species
Mothership and North
Pacific ocean perch
Pacific trawl and
North Pacific
longline-gillnet
Sablefish
Landbased trawl
All species
All fisheries
Flounders
Pollock
Herring
Other species
All fisheries
Rockfish
Other species
0,000
1,300,000
1,100,000
none
none
160,000
3,000
33,000
15,000
4,600
4,600
3,000
none
none
35,000
none
none
9,600
none
none
1,200
none
none
8,500
),000
100,000
none^
none
none
210,000
none
none
30,000
none
none
120,000
none
none
12,000
none
none
16,000
^Included in quota for other species.
1032 Fisheries biology
In March 1977, the United States implemented
a preliminary fishery management plan for the
groundfish fishery of the Bering Sea and Aleutian
Islands region, as directed by the FCMA. The final
fishery management plan is expected to be imple-
mented in 1980. The FCMA established regional
management councils, with the North Pacific Fishery
Management Council having responsibility for re-
sources within the 200-mile fishery conservation zone
of Alaska (Fig. 60-13). The State of Alaska retains
jurisdiction over waters within three miles of its
coast.
The specific objectives of the FCMA are to (1)
continue rebuilding the halibut resource; (2) rebuild
depleted and maintain healthy groundfish stocks at
levels capable of producing maximum sustainable
yields; (3) provide an opportunity for U.S. fishermen
to participate in the use of Bering Sea/Aleutian
Islands resources, limited only by the objectives of
1 and 2 above, (4) allow foreign use of the resources,
consistent with objectives 1, 2, and 3 above; and (5)
reduce conflicts between users of mobile and sta-
tionary gear (North Pacific Fishery Management
Council 1979).
The plan contains specific measures to accomplish
these objectives through control of fishery vessels
operating in the zone, requirements for reporting
catches by statistical area, time-area closures, catch
limitations, and nonretention of species of special
interest to U.S. fishermen such as salmon, crab, and
Pacific halibut (North Pacific Fishery Management
Council 1979). Potential and current yields have
been derived by assessing the condition of the various
species or species groups from commercial and
research vessel data and population dynamics theories
and models. The techniques used to analyze the data
have varied considerably from species to species
depending on the quality and completeness of the
available data (North Pacific Fishery Management
Council 1979). To assure that lack of information
does not cause the resources to be overexploited,
generally conservative estimates of yields have been
used. For each resource the biological productive
potential has been determined in terms of maximum
sustainable yield (MSY),^ current equilibrium yield
^ MSY is the average yield over a reasonable length of time of
the largest catch which can be taken continuously from a
stock under current environmental conditions.
150°
156°
168° 174° 180° 174° 168° 162° 156° 150° 144° 138° 132° 126° 120° 114°
Figure 10-13. The eastern Bering Sea/Aleutian Islands U.S. fishery conservation zone (shaded area).
(EY),-' and acceptable biological catch (ABC).'*
It is generally recognized by fisheries scientists that
the MSY concept suffers from fundamental inade-
quacies (North Pacific Fishery Management Council
1979). The concept has been retained, however,
as a useful basis for making management decisions if
the limitations and underlying assumptions are
recognized and taken into account.
^EY is the annual or seasonal harvest which allows the stock
to be maintained at approximately the same level of abun-
dance (apart from the effects of environmental variation) in
succeeding seasons or years.
''ABC is a seasonally determined catch that may differ from
MSY for biological reasons; it can be lower or higher than
MSY for species with fluctuating recruitment, and may be set
lower than MSY in order to rebuild overfished stocks.
Demersal fish 1 033
Values of MSY, EY, and ABC for 1979 as deter-
mined by the North Pacific Fishery Management
Council and the IPHC for Pacific halibut are given in
Table 60-11. The values apply to both the eastern
Bering Sea and Aleutian Islands areas, except for
Pacific ocean perch and sablefish, which are managed
as independent stocks in each area. A leirge propor-
tion of catches of all other species except Atka
mackerel and squid is taken in the eastern Bering Sea.
Atka mackerel are targeted in the Aleutian Islands
area, whereas in the eastern Bering Sea they are only
an incidental part of catches. Squid are included in
the groundfish management plan because they are
targeted by the Japanese groundfish trawl fishery.
The fishery for squid has been centered in the eastern
Bering Sea in some years and in the Aleutian area in
other years.
TABLE 60-11
MSY, EY, and ABC values (X 10^ mt) for groundfish in the eastern Bering Sea/Aleutian Islands region in 1979
(North Pacific Fishery Management Council 1979).
Species
Management
area(s)^
MSY
EY
ABC
Pollock
BS-AL
Yellowfm sole
BS-AL
Greenland turbot and
BS-AL
arrowtooth flounder
Other flatfishes
BS-AL
Pacific cod
BS-AL
Rockfishes
BS
AL
Sablefish
BS
AL
Atka mackerel
BS-AL
Squid
BS-AL
Pacific halibut
BS-AL
Other included species
BS-AL
TotaF
BS-AL
1,100-1,600
1,000
1,000
169-260
117
117
100
90-95
90
44.3-76.8
61
61
58.7
58.7
58.7
32
6.5^
6.5^
75
15
15
11.35
3.5
3.5
1.85
1.5
1.5
33
Unknown
24.8
>10
>10
10
5
0.3
d
89.4
89.4
74.2
1724.6-2348.1
1,452.6-1457.6
462.2
*BS = Eastern Bering Sea area; AL = Aleutian Islands area.
^Pacific ocean perch only.
'^All rockfishes including Pacific ocean perch.
'^Determined by International Pacific Halibut Commission.
^Excluding Pacific halibut.
1 034 Fisheries biology
The management plan also has provisions to con-
sider economic, social, and ecological objectives in
developing appropriate catch levels. The incorpora-
tion of these considerations may produce catch
levels (Optimum Yield, OY) that are higher or lovi^er
than ABC. For example, OY may be set higher than
ABC in order to produce higher yields from other
more desirable species in a multispecies fishery
(North Pacific Management Council 1979). OY may
also be set lower than ABC to provide larger fish
or a higher average catch-per-unit-effort.
In the eastern Bering Sea and Aleutian Islands
regions, there is currently only a modest domestic
involvement in the fishery, and no social or economic
factors have been identified at present to alter values
of ABC. OY is, therefore, considered equivalent to
ABC.
From OY values and the expected domestic
annual harvest (DAH), the total allowable level of
foreign fishing (TALFF) for each species is deter-
mined, based on the following equation:
TALFF = OY - DAH - Reserve
To allow for any unexpected development of the
domestic fishery and to prevent OY's from being
exceeded, the plan also provides for a reserve which
is released during the year to the domestic fishery,
or, if not used by the domestic fishery, to the foreign
fisheries. Any of the DAH not used by the domestic
fishery is also released to foreign fisheries. Levels
of reserve, initial DAH, and initial TALFF for differ-
ent resources for 1979 are given in Table 60-12. A
special ABC or OY of 100,000 mt of pollock for the
Aleutian Islands area is also shown in Table 60-12.
This additional quota is designed to support any
exploratory or experimental fishery for pollock over
the central Bering Sea deepwater basin. A dispersed
but relatively large population of pollock has been
discovered in pelagic waters of this region in recent
years by Japanese research vessel surveys (North
Pacific Fishery Management Council 1979).
TABLE 60-12
Values of OY, reserve, and initial values of DAH and TALFF for fishery resources of the eastern Bering Sea
and Aleutian Islands region in 1979 (North Pacific Fishery Management Council 1979).
Species group
Management
area(s)^
ABC or OY
Reserve
Initial
DAH
Initial
TALFF
Pollock
BS-AL
AL
1,000,000
100,000^
50,000
19,550
930,450
100,000
Yellowfin sole
BS-AL
117,000
5,850
2,050
109,100
Greenland turbot and
arrowtooth flounder
BS-AL
90,000
4,500
1,075
84,425
Other flatfishes'^
BS-AL
61,000
3,050
1,300
56,650
Pacific cod
BS-AL
58,700
2,935
24,265
31,500
Pacific ocean perch
BS
AL
3,250
7,500
162
375
1,380
1,380
1,708
5,745
Other rockfishes
BS-AL
7,727
500
1,550
5,677
Sablefish
BS
AL
3,500
1,500
350
150
700
700
2,450
650
Atka mackerel
BS-AL
24,800
1,240
100
23,460
Squid
BS-AL
10,000
500
50
9,450
Others
BS-AL
74,249
3,712
2,000
68,537
Total
BS-AL
1,559,226
73,324
56,100
1,429,802
*BS = Eastern Bering Sea area; AL = Aleutian Islands area.
''See text for explanation of this special allocation.
'^Excluding Pacific halibut.
Demersal fish 1 035
I
I
I
I
i
REFERENCES
Bakkala, R., L. L. Low, and V. Wespestad
1979 Condition of groundfish resources in
the Bering Sea and Aleutian area.
Nat. Mar. Fish. Serv., Northwest and
Alaska Fish. Cent., Seattle, Washing-
ton. Unpub. MS.
Bell, F. H.
1967 The halibut fishery, Shumagin Islands
and westweird not including Bering
Sea. Int. Pac. Halibut Comm., Rep.
45.
Best, E. A.
1977 Distribution and abundance of juve-
nile halibut in the southeastern
Bering Sea. Int. Pac. Halibut Comm.,
Sci. Rep. 62.
Bower, W. T.
1927-53 Alaska fishery and fur seal indus-
tries in 1926-50. U.S. Dep. Comm.,
Bur. Fish. App. to Rep. Comm.
Fish, for 1926-1939, Stat. Digest for
1940-50.
Chikuni, S.
1975 Biological study of the population
of the Pacific ocean perch in the
North Pacific. Fish. Agency of
Japan, Far Seas Fish. Res. Lab.
12:1-119.
Chitwood, P. E.
1969 Japanese, Soviet, and South Korean
fisheries off Alaska: Development and
history through 1966. U.S. Fish
Wildl. Serv., Circ. 310.
Cobb, J.N.
1927 Pacific cod fisheries. Rep. U.S.
Comm. Fish., 1926, append. 7:
385-499.
Dunlop, H. A., F. H. Bell, R. J. Myhre, W. H.
Hardman, and G. M. Southward
1964 Investigation, utilization, and regula-
tion of the halibut in southeastern
Bering Sea. Int. Pac. Halibut Comm.,
Rep. 35.
Enforcement and Surveillance Division
1971, 1973 Foreign fishing activities
Bering Sea and Gulf of Alaska, 1970,
1971. Nat. Mar. Fish. Serv., Juneau,
Alaska, Unpub. MS.
Forrester, C. R., A. J. Beardsley, and Y. Takahashi
1978 Groundfish, shrimp, and herring fish-
eries in the Bering Sea and northeast
Pacific— historical catch statistics
through 1970. Inter. N. Pac. Fish.
Comm. Bull. 37.
Gershanovich, D. E., N. S. Fadeev, T. G. Lyubimova,
P. A. Moiseev, and V. V. Natanov
1974 Principal results of Soviet oceanog-
raphy investigations in the Bering
Sea. In: Oceanography of the Bering
Sea, D. W. Hood and E. J. Kelley,
eds., 363-70. Inst. Mar. Sci., Occ.
Pub. No. 2, Univ. of Alaska, Fair-
banks.
Haskell, W. H.
1964
Foreign fishing activities Bering Sea
and Gulf of Alaska, 1963. U.S. Fish
Wildl. Serv., Bur. Comm. Fish., Off.
of Res. Man., Juneau, Alaska, Unpub.
MS.
Hoag, S. H.
1975 Survival of halibut released after
capture by trawls. Int. Pac. Halibut
Comm. Sci. Rep. 57.
1976 The effect of trawling on the setline
fishery for halibut. Int. Pac. Halibut
Comm. Sci. Rep. 61.
Hoag, S. H., and R. R. French
1976 The incidental catch of halibut by
foreign trawlers. Int. Pac. Halibut
Comm., Sci. Rep. 60.
International Pacific Halibut Commission
1977 The Pacific halibut fishery: catch,
effort, and CPUE, 1929-75. Int.
Pac. Halibut Comm. Tech. Rep. 14.
1979 Items of information on the halibut
fishery in the Bering Sea and the
Northeastern Pacific Ocean requested
for INPFC. Int. Pac. Halibut Comm.,
Seattle, Wash., Unpub. MS.
1036 Fisheries biology
Law Enforcement Division
1974, 1975, and 1977 Foreign fishery
activities Bering Sea and Gulf of
Alaska, 1972-1974. Nat. Mar. Fish.
Serv., Juneau, Alaska. Unpub. MS.
North Pacific Fishery Management Council
1979 Bering Sea and Aleutian Islands
groundfish fishery; proposed imple-
mentation of fishery management
plan. Fed. Reg. 44 (224): 66356-
463.
Office of Enforcement and Surveillance
1965, 1967-1970 Foreign fishing activities
Bering Sea and Gulf of Alaska, 1964-
1969. Nat. Mar. Fish. Serv., Juneau,
Alaska. Unpub. MS.
Pereyra, W. T., J. E. Reeves, and R. G. Bakkala
1976 Demersal fish and shellfish resources
of the eastern Bering Sea in the
basehne year 1975. Nat. Mar. Fish.
Serv., Northwest Fish. Cent., Seattle,
Wash.
Shuntov, V. P.
1970
and E. J. Kelley, eds., 119-36. Inst.
Mar. Sci., Occ. Pub. No. 2, Univ. of
Alaska, Fairbanks.
Seasonal distribution of black and
arrowtoothed halibuts in the Bering
Sea. In: Soviet fisheries investigations
in the northeastern Pacific, P. A.
Moiseev, ed., 5:397-408. (Transl.
Israel Prog. Sci. Transl., Jerusalem,
1972.)
Skud, B. E.
1977 Regulations of the Pacific halibut
fishery, 1924-1976. Int. Pac. Hali-
but Comm., Tech. Rep. 15.
Thompson, W. F., and N. L. Freeman
1930 History of the Pacific halibut fishery.
Int. Pac. Halibut Comm., Rep. 5.
Pruter, A. T.
1976 Soviet fisheries for bottomfish and
herring off the Pacific and Bering
Sea coasts of the United States.
Mar. Fish. Rev. 38: 1-14.
Sasaki, T.
1977
1979
Sharma, G. D.
1974
Outline of the Japanese groundfish
fishery in the Bering Sea, 1976
(November 1975-October 1976). Fish.
Agency of Japan, Tokyo. Unpub.
MS.
Preliminary report on blackcod and
Pacific cod survey by Ryusho Maru
No. 15 in the Aleutian Region and
the Gulf of Alaska in the summer
of 1979. Fish. Agency of Japan,
Tokyo. Unpub. MS.
Contemporary depositional environ-
ment of the eastern Bering Sea. I.
Contemporary sedimentary regimes of
the eastern Bering Sea. In: Oceanog-
raphy of the Bering Sea, D. W. Hood
Wakabayashi, K., and R. Bakkala
1978 Estimated catches of flounders by
species in the Bering Sea— updated
through 1976. Nat. Mar. Fish. Serv.
Northwest and Alaska Fish. Cent.,
Seattle, Wash. Unpub. MS.
Wakabayashi, K., R. Bakkala, and L. Low
1977 Status of the yellowfin sole resource
in the eastern Bering Sea through
1976. Nat. Mar. Fish. Serv., North-
west and Alaska Fish. Cent., Seattle,
Wash., Unpub. MS.
Wilimovsky, N. J.
1974 Fishes of the Bering Sea: The state
of existing knowledge and require-
ments for future effective effort.
In: Oceanography of the Bering
Sea, D. W. Hood and E. J. Kelley,
eds., 243-56. Inst. Mar. Sci., Occ.
Pub. No. 2, Univ. of Alaska, Fair-
banks.
Eastern Bering Sea Crab Fisheries
Robert S. Otto
National Marine Fisheries Service
Kodiak, Alaska
ABSTRACT
Eastern Bering Sea fisheries for red king crab (Paralithodes
camtschatica), blue king crab (P. platypus), and Tanner
crabs (Chionoecetes bairdi and C. opilio) are among the most
important sources of crab in the world. Eastern Bering Sea
crab fisheries currently provide about 12 percent of world
crab landings, and some 38 percent of domestic crab landings.
Fully 50 percent of the landed value of the U.S. crab catch
came from the eastern Bering Sea in 1978.
The history of eastern Bering Sea crab fisheries extends
back to 1930, but substantial commercial efforts were not
undertaken until the 1950's, when the king crab fisheries were
developed. Tanner crab fisheries were developed during the
1960's. Japan and the Soviet Union had large crab fisheries
in the eastern Bering Sea before the United States mounted a
substantial effort. Foreign fisheries for king crabs ceased in
1974 and are now prohibited. Japan continues to fish Tanner
crab in the eastern Bering Sea, but the Soviet Union left the
fishery in 1971.
Record landings of crabs in the eastern Bering Sea over the
past five years have prompted the development of one of the
newest and most efficient U.S. fishing fleets. The economic
future of eastern Bering Sea crab fisheries is clouded by
forecast declines in the abundance of red king crab and con-
tinued low abundance of C. bairdi. Development of new
markets wUl be necessary if the C. opilio stock is to be fully
exploited. Without further development of the C. opilio
fishery, the importance of the eastern Bering Sea as a source
of crab is likely to decline.
INTRODUCTION
Eastern Bering Sea fisheries for king crab (Paralith-
odes spp.) and Tanner crab (Chionoecetes spp.) are
among the most important of Alaska's fisheries.
Their history dates from 1930; they are multinational
in scope and provide substantial portions of the world
crab supply. These fisheries have been extremely
lucrative in recent years and have received much
attention in fisheries, ship building, and financial
circles. For example, the number of U.S. vessels
fishing for red king crab (P. camtschatica) in the
eastern Bering Sea increased from 57 in 1970 to 104
in 1975 and reached 236 in 1979. The valuable
catches of king and Tanner crab in 1978 were the
primary reason why Dutch Harbor was the most
productive fishing port in the United States, with
landings worth $99,700,000. My purpose is to
provide a review of eastern Bering Sea crab fisheries
and to shed some Ught on their possible future.
CONTRIBUTION TO WORLD AND
NATIONAL CRAB LANDINGS
The world catch of crabs increased from 404,800
mt in 1976 to 448,800 mt in 1977 (Food and Agri-
cultural Organization 1978). Of the 44,000 mt
increase, 10,300 mt (23 percent) came from increased
yield in the eastern Bering Sea. Taken together, all
nations' landings of king and Tanner crabs made up
31 percent (127,000 mt) of the world crab catch in
1976 and 28 percent (127,500 mt) in 1977. Land-
ings of king and Tanner crabs in the eastern Bering
Sea were 11 percent (44,100 mt) and 12 percent
(54,400 mt) of the world crab catch in 1976 and
1977. Given the expansion of the U.S. crab fisheries
in the region since 1977, it seems probable that the
eastern Bering Sea currently provides more than 12
percent of the world's crab supply.
On the domestic front, king and Tanner crabs are
more important, providing 58 percent of the domes-
tic crab catch in 1978, and tending to supplant the
East Coast blue crab (Callinectes sapidus) in recent
years (Fig. 61-1 and Table 61-1). In 1978, the
eastern Bering Sea crab catch provided 50 percent
of the value of U.S. crab landings. Tanner crab have
become more important in recent years and are
currently about as important as king crab in landed
weight. In terms of landed value, king crab have
been, and continue to be, our most important crab
fishery, although the relative importance of Tanner
1037
1 038 Fisheries biology
1978
AVERAGE
1969-1978
Figure 61-1. Relative contributions of various species
of crabs to the total weight of United States crab landings.
crab has been increasing (Fig. 61-2). The relative
value of king and Tanner crab fisheries has grown,
while that of blue crab and dungeness crab (Cancer
magister) has declined. According to the Alaska
Department of Fish and Game (1980) the 1979
ex-vessel value of domestic crab landings in the
eastern Bering Sea was $100,670,000 for king crabs
and $32,400,000 for Tanner crabs.
The contribution of the eastern Bering Sea to king
crab catches within 200 miles of Alaska began in-
creasing rapidly in the early 1970's, with more than
50 percent caught there in each year since 1974
(Fig. 61-3). For the years after 1974 (when foreign
fishing ceased). Fig. 61-3 provides an index of the
eastern Bering Sea contribution to total domestic
king crab landings. ADF&G landing statistics show
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Crab fisheries 1 039
, TANNER CRABS
1978
AVERAGE
1969-1978
Figure 61-2. Relative contributions of various crabs to
the landed value of United States crab landings.
that the 1979 eastern Bering Sea king crab catch was
about 49,000 mt or 78 percent of the estimated
68,000 mt total Alaskan catch of king crab.
The importance of Tanner crab fisheries in the
eastern Bering Sea relative to other areas in Alaska
declined from 1965 until 1973. This decline was
due to decreasing foreign catch as well as developing
U.S. fisheries for Tanner crab along the south side
of the Alaska Peninsula and around Kodiak Island.
Since 1973, the importance of the catch of Tanner
crab in the eastern Bering Sea has increased relative
to other areas, and in 1977, 1978, and 1979 the
eastern Bering Sea provided most of the Tanner
crab taken within 200 miles of Alaskan shores.
Since the Japanese still participate in eastern Bering
PERCENT OF TOTAL CATCH
Figure 61-3. Relative contributions of eastern Bering Sea
crab fisheries to domestic landings of king and Tanner
crabs.
Sea Tanner crab fisheries. Fig. 61-3 does not pro-
vide an index of the contribution of the eastern
Bering Sea to domestic landings. In 1978, the domes-
tic landings from the eastern Bering Sea were 30,800
mt or 52 percent of U.S. Tanner crab landings
(58,700 mt). The 1979 catch provided a similar pro-
portion of domestic landings.
HISTORICAL DEVELOPMENT
Commercial crab fisheries in the eastern Bering
Sea began in 1930, when a Japanese ship processed
about one million red king crab in the area north
of the Alaska Peninsula (Harrison et al. 1942,
Miyahara 1954). There was no fishing in 1931, but
one or two factory ships operated in the area each
year from 1932 to 1939. Some 7.6 million crab
were taken over the eight-year period (Miyahara
1954). There was no further Japanese fishing until
1953.
Exploratory fishing by the United States began in
1940 (Harrison et al. 1942, Ellson et al. 1949)
and was renewed in 1947 (King 1949, Ellson et al.
1950). By 1949 all major stocks of red king crab in
Alaska had been discovered. The distribution of blue
king crab (P. platypus) was also fully described.
Commercial operations in the eastern Bering Sea by
the United States yielded 4,250 mt of red king crab
from 1949 to 1952. Domestic trawlers continued to
fish for crab until 1959 but catches were small.
In 1953, with the renewal of Japanese crab fisher-
ies and the inclusion of crab fisheries in Intemationad
North Pacific Fisheries Commission (INPFC) nego-
tiations, eastern Bering Sea crab fisheries entered
what may be called the modern era. Since 1953,
1040 Fisheries biology
these fisheries have been continuous, generally
expanding, and multinational in scope (with the
U.S.S.R. entering the fishery in 1959). King crabs
continued to be the focus of interest and provided
economic support for fishery development of Tanner
crab and, to a lesser extent, groundfish resources.
Both commercial species of Tanner crab (C.
bairdi and C. opilio) were probably taken incidentally
in eastern Bering Sea king crab fisheries as early as
1953 (Fisheries Agency of Japan 1956). Japanese
processing of Tanner crabs amounted to 2,848
cases of 48 half-pound cans in 1955. Reports on
early Japanese Tanner crab fishing are vague and no
Tanner crab pack was reported from 1956 to 1964.
A directed Japanese Tanner crab fishery developed in
response to declining abundance of red king crab
(Hoopes and Greenough 1970) and an increasingly
aggressive negotiating posture assumed by the United
States after the 1958 Convention on the Continental
Shelf entered into force in 1964 (Congressional
Research Service 1974). Approximately 1.7 million
Tanner crab were taken by the U.S.S.R. and Japan in
1965. The fishery expanded rapidly and some 24.2
million Tanner crab were taken by foreign fleets in
1969, when the United States entered the fishery.
High abundance of Tanner crab relative to king crab
during the late 1960's probably accelerated fishery
development.
Bilateral agreements concerning crab fisheries
were concluded between the United States and
Japan in 1964, and between the United States and
the Soviet Union in 1965 (Congressional Research
Service 1974). Tanner crab research under the
auspices of INPFC began in 1965. Considerable
information on Tanner crab fisheries became avail-
able after these developments and as a result of
pursuant negotiations.
By 1969, all major stocks of Bering Sea crabs
were being exploited. Fisheries for red king crab
were fully developed, and those for blue king crab
were nearing full development. Fisheries for Tanner
crabs, however, promised considerable new develop-
ment in the 1970's.
KING CRAB STOCKS
Of the two commercially important species of
king crabs found in the Bering Sea, red king crab
(P. camtschatica) have always made up more than 83
percent of the catch. The distribution of red king
crab covers much of the eastern Bering Sea and is
generally associated with the continental land mass
(Fig. 61-4). The vast majority of red king crab
landings have come from outer Bristol Bay and the
area immediately north of the Alaska Peninsula.
Figure 61-4. Distribution of red king crab (Paralithodes
camtschatica) in the eastern Bering Sea. Darkly shaded
portions indicate areas of consistent abundance.
Fisheries for blue king crab (P. platypus) made up
17 percent of the eastern Bering Sea king crab catch
in 1974 but did not exceed 12 percent in other
years. The distribution of blue king crab in the
eastern Bering Sea tends to be associated with off-
shore areas near islands (Fig. 61-5). This contrasts
sharply with the distribution of blue king crab south
of the Alaska Peninsula, where stocks and fisheries
are typically found in bays and frequently in associa-
tion with glaciers. The Pribilof Islands fishery has
been most important.
Golden king crab (Lithodes aequispina) are found
in the eastern Bering Sea along the continental shelf
break in deeper waters. National Marine Fisheries
Service (NMFS) trawl surveys have not encountered
this species in waters shallower than 128 m. Golden
king crab are fished in southeastern Alaska and in
the Adak Island area but do not occur in the eastern
Bering Sea catch. Golden king crab are, however,
the most frequently occurring king crab in the
incidental catch of Japanese and Soviet trawl fisheries
in the eastern Bering Sea (Nelson et al. in press).
No estimates of golden king crab abundance are
available .
Crab fisheries 1041
180°
170°
160°
65'
C
&.J1,^ ^
"^^^
r KOTZEBUE
'-W SOUND
'^ ' 3\.
\
NORTON SOUND
65'
ST. LAWRENCE ^-^tT^
ISLAND S
!b
Is /
60<
;:;:;::::::::;:;:;
Ol
' KUSKOKWIM
\: BRrSTOL
£■„.,,. BAY
ST. MATTHEW -iuii^i^^'
ISLAND ■■■■^^■'■
60
PRIBILOF IllJ^i^S:'
ISLANDS ;:;|^pn
^^■,
55'
.-g:^
BLUE KING CRAB
/^
"^^u
55
L
Figure 61-5. Distribution of blue king crab (Paralithodes
platypus) in the eastern Bering Sea. Darkly shaded portions
indicate areas of consistent abundance.
Trawl surveys conducted by the NMFS, explora-
tory fishing efforts, and distributions of U.S. as well
as foreign fisheries all suggest that currently exploited
Bering Sea king crab resources are divisible into four
manageable units or stocks. In order of their impor-
tance, these are: (1) southeastern Bering Sea red
king crab, (2) Pribilof Islands blue king crab, (3)
northern Bering Sea red king crab (mostly Norton
Sound), and (4) northern Bering Sea blue king crab
(mostly St. Matthew Island area).
KING CRAB FISHERIES
Domestic fishery
Until 1973, the southeastern Bering Sea red king
crab fishery accounted for virtually all U.S. crab
landings in the eastern Bering Sea. For most of
its history the fishery was conducted in waters
north of Unimak Island and the Alaska Peninsula,
from Cape Sarichef to Port Heiden. In 1973, U.S.
fishermen began taking blue king crab in the Pribilof
Islands area. In 1977, exploratory fishing efforts
in Norton Sound yielded some 240 mt of red king
crab, indicating some potential for expansion. Ex-
ploratory fishing for blue king crab in the St.
Matthew Island area also began in 1977 (Lechner
1979).
Domestic eastern Bering Sea crab fisheries have
been managed by the ADF&G since 1959 through a
combination of restrictions on size, sex, and total
catch of crab taken, as well as seasonal closures and
gear restrictions. Compliance with regulations is
ensured through landing laws. Before 1959, the
fishery was managed by the U.S. Bureau of Fisheries.
Taking female and soft-shelled crab has been prohib-
ited throughout the history of the fishery. The use
of tangle nets was prohibited in 1954, and trawling
was prohibited in 1960. Currently, pots are the only
legal commercial gear for taking crab in the eastern
Bering Sea. The history of size limits, seasons, and
quotas (Table 61-2) is complex. Basically, regulations
are designed to protect the reproductive capability of
crab stocks, maintain product quality, minimize
dead-loss, and maintain high catch while minimizing
year-to-year fluctuations. Minimizing fluctuations
amounts to attempting to provide a fishery consisting
of more than one year-class. Katz and Bledsoe
(1977) and Fukuhara (1974) provide more detailed
considerations of Alaska shellfish regulations. A
fishery management plan for Alaska king crabs is
currently under development by the North Pacific
Fishery Management Council.
The Bering Sea management area (ADF&G sta-
tistical area "Q") includes all waters of the Bering
and Chukchi seas north of 55°36'N latitude (ADF&G
1979a). In 1978 area Q was divided into Southeast-
ern, Pribilof, and Northern districts. These districts
effectively result in separate management of fisheries
for the four stocks discussed above. The Northern
district includes all waters north of 58°39'N latitude
and the two southern districts are separated at 168° W
longitude.
Fishermen from the United States began taking
king crab in the Bering Sea with trawling gear in
1947, but catches were small before 1953, when the
catch was only 900 mt (Table 61-3). There was a
gradual dechne in effort and catch until 1959, when
no United States king crab catch was reported.
Available markets were filled by the rapidly growing
fisheries around Kodiak Island, near Adak Island, and
on the south side of the Alaska Peninsula. A period
of fluctuating, low catches (less than 450 mt) followed
from 1960 through 1966. The U.S. crab fishery
began to expand in 1967 as a result of declining
catches in other areas. The U.S. catch increased
rapidly, reaching 5,900 mt in 1971, and has increased
each year since 1971 (Table 61-3). Landings of
1042 Fisheries biology
TABLE 61-2
Legal seasons, size limits, and guideline harvest ranges (quotas) in domestic eastern Bering Sea crab fisheries, 1959 to present
Period
Season
Month/Day
Size limits'
mm
Harvest range^
mt (1,000's)
Southeast district (red king crab)
Pribilof Islands (blue king crab)
Northern district (red king crab)
Northern district (blue king crab)
1959-1965
None
165
None
1/66-8/68
None
146
None
8/68-3/69
None
178
None
4/69-7/693
None
146
None
8/69-3/70
None
178
None
4/70-8/70
None
146
None
9/70-3/71
None
178
None
4/71-10/71
None
179
None
10/71-12/71
1972^
1/1-3/31
6/1-12/31
159
None
1973^
1/4-4/14
165
10.4
6/15-12/31
165
19744,5
7/29-
165
10.4
1975^
8/1-
165
14.0
1976^
8/15
165
18.1-29.5
1977^
9/15-
165
24.9-38.5
1978^
9/15-
165
27.2-40.8
1979^
9/10-
165
40.8-49.9
1974^
4/15-6/15
165
2.3-3.6
1975-1979'
9/15-
165
2.3-3.6
1977
6/7-9/3
None^
1978
1/1-5/30^
121
0.1-4.2
7/15-9/3
121
0.2-0.5
1979
1/1-5/30^
121
0.9-1.4
7/15-9/3
121
0.1-0.2
1977
6/7-9/3
140
None^
1978
6/7-9/3
140
0.7-1.4
1979
7/15-9/3
140
0.7-1.4
' Carapace width measured outside spines.
^Fishery managed by quota from 1973 to 1975 and by range since 1975. Ranges are chosen to reflect precision of abundance
estimates. Closures occur by emergency order of the commissioner of ADF&G.
3 From 1969 to 1971 domestic size limits were lowered to those of foreign fisheries during the period of time when foreign
fisheries were operating.
^ From 1972 to 1974 size limits were lowered from March through October as in footnote 3.
^ Legal season extends through April 15 of the following year. Closures have been accomplished by emergency order due to
harvest limits each year since 1974 on dates ranging from October 12 to December 8.
* Pribilof Island blue king crab considered with southeastern red king crab before 1974.
'Legal season extends to May 31 of following year. Closures have been accomplished by emergency order on dates ranging from
October 20 to May 20 of the following year.
^ Opening and closure by emergency order.
^Subsistence fishery.
Pribilof Islands blue king crab peaked at 4,000 mt in
1974 (Fig. 61-6) and have since stabilized at about
2,700 mt.
Rising U.S. interest in harvesting Bering Sea king
crab led to a rapid increase in effort (Table 61-4 and
Fig. 61-7). Nine U.S. vessels fished for king crab
in the eastern Bering Sea in 1966 with a total effort
of 2,720 pot Hfts. By 1970, there were 51 vessels
and 96,700 pot lifts. In 1975, 194 vessels applied
an effort of 205,100 pot lifts in the southeast Bering
Sea red king crab fishery and 20 vessels applied
16,300 pot lifts in the Pribilof Islands blue crab
Crab fisheries 1043
TABLE 61-3
Estimated annual red and blue king crab catches in the Southeastern and Pribilof districts of the eastern Bering Sea by the
United States, Japan, and U.S.S.R., 1953-75.'
United States
Japan^
U.S.S.R.^
Year^
Red
Blue
Red
Blue
Red
Total
1953
2,000
—
11,365
—
0
13,356
1954
2,329
—
8,086
—
0
10,415
1955
1,878
—
8,693
—
0
10,571
1956
1,896
—
8,308
—
0
10,204
1957
588
—
8,548
—
0
9,136
1958
7
—
8,136
—
0
8,143
1959
0
—
9,432
—
2,170
11,602
1960
598
—
13,838
—
10,773
25,209
1961
459
—
21,823
—
18,581
40,863
1962
74
—
35,152
—
18,114
53,340
1963
747
—
36,142
—
20,529
57,418
1964"*
910
—
40,676
—
22,400
63,986
1965
1,762
—
24,406
—
13,579
43,167
1966
997
—
27,908
2,010
14,080
44,995
1967
3,102
—
21,675
2,415
8,438
35,630
1968
8,687
—
23,063
1,598
3,020
36,368
1969
10,403
—
6,749
5,482
1,882
24,516
1970
8,559
—
9,952
1,282
1,696
21,489
1971
12,995
—
3,554
1,230
1,404
19,183
1972
21,744
—
4,421
300
—
26,465
1973
26,913
1,277
1,234
45
—
29,469
1974
42,266
7,107
886
1,732
—
51,991
1975^
49,686
2,434
—
-
—
52,120
1976
63,044
7,366
—
—
—
70,410
1977
69,968
8,499
—
—
—
78,467
1978
87,618
6,516
—
—
—
94,134
1979
107,828
7,602
115,430
'Weights in thousands of pounds (1,000 pounds = 0.0454 metric tons); all estimates were made by multiplying number of
reported catch times an estimate of average weight.
^Weight estimates before 1966 are derived from INPFC statistics; average weights since 1966 are as reported by ADF&G.
^Average weights computed from average carapace lengths and pack data given in INPFC annual reports (mostly Hoopes et al.
1972) and the length-weight relationship given by Wallace et al. (1949).
^ Data for Japanese landings of blue king crab are derived from presentations at plenary sessions of INPFC.
^ ADF&G catch statistics include estimated dead loss (1975-79); landings are about 5 percent lower than catch in most years.
fishery. Effort in pot lifts per year doubled between
1974 and 1977, but decreased somewhat in later
years (Table 61-4).
Fishing equipment
Most of the Bering Sea crab fleet (70 percent in
1977) consists of Seattle-based vessels that operate
seasonally in the Bering Sea, although the proportion
of Alaskan vessels and crews has increased in recent
years. Bering Sea crab fishermen and vessel operators
earn their livelihood primarily from king and Tanner
crab fishing. The domestic fleet consists of modern
steel-hulled vessels designed for use in the North
Pacific and Bering Sea. Crab vessels are typically
capable of carrying 24,000-35,000 live king crab in
holds with circulating sea water. According to
ADF&G statistics for the 1977 season, keel lengths
ranged from 14 to 46 m, with an average length of
28.4 m and weight of 138 net tons. While the average
keel length of Bering Sea crab vessels has been fairly
constant, ranging from 26 to 29 m, the average
tonnage has increased from 45 tons in 1966 to 138
tons in 1977. Total tonnage in the fleet increased
from 675.0 tons (9 vessels) to 19,376 net tons in
1977 (130 vessels). The number of vessels in the
fishery increased to 162 in 1978 and 236 in 1979.
Given the trend toward increased net tonnage per
vessel, it is probable that the current tonnage in the
1044 Fisheries biology
100
90
80
5 70
X 50
o
<
O
30
40
20 -
10
RED KING CRAB
BLUE KING CRAB
I r I I I I T f
V .
54 56 58 60 62 64 66 68 70 72 74 76 78
YEAR
Figure 61-6. All-nation landings of red and blue king crabs from the eastern Bering Sea south of 58°.
fishery is nearly double that of 1977 (perhaps 40,000
net tons).
King crab pots are constructed with steel frames
(often concrete reinforcing bar) and nylon web. Pots
usually exceed 227 kg in weight. The newest crab
vessels can carry 160-200 pots on deck and many
vessels fish over 300 pots. During the 1977 red
king crab season the ADF&G conducted a detailed
gear survey that included about half the fleet (74
vessels). The average number of pots per vessel was
239. The gear consisted of square pots, approxi-
mately 0.9 m tall, with the following characteristics:
Size
Frequency
Average weight
(Percent)
(kg)
1.8
3
255
2.0
22
286
2.1
73
303
2.3
1
328
3.0
1
409
Norton Sound fishery
Two separate fisheries for red king crab occur in
Norton Sound. A winter fishery is conducted by
residents of the Nome area using pots, ring nets, and
hand lines set through holes or leads in the ice.
Winter fishing is primarily for subsistence (personal
use). The subsistence fishery is small and has prob-
ably never exceeded 45 mt. Some 6.4 mt of red king
crab taken in winter fishery were sent to Kodiak via
air freight, in 1978. These crab were processed
commercially. A summer commercial fishery has been
conducted in Norton Sound each year since 1977.
Catches were 242 mt in 1977, 950 mt in 1978, and
1,300 mt in 1979. Norton Sound red king crab are
small; commercially taken crab typically average 1.4
kg as compared to 2.7 kg in the southeastern Bering
Sea fishery. In spite of effort that increased from
seven vessels in 1977 to nine vessels in 1978 and 34
Crab fisheries 1045
CO
o
Li.
650
600
550
500
450
400
350
300
250
200
150
100
50
JAPAN TAN
JAPAN POT
/\
\ / \^^ t
v
us POT / \
/
i^M^^^^^^^^^^^
y
/
/
^mM
1200
1100
1000
900
800
■0
O
H
700
600
r
■n
H
CO
500
X
400
o
300
200
100
54 56 58 60 62 64 66 68 70 72 74 76 78 80
YEAR
Figure 61-7. All-nation effort in eastern Bering Sea king crab fisheries (see text for explanation of Japanese effort).
vessels in 1979, catches have not increased greatly.
The 1979 catch, however, approached the upper limit
of the allowed harvest (quota) range of 1,400 mt.
St. Matthew fishery
In 1977, exploratory blue king crab fishing in the
St. Matthew Island area yielded 500 mt.
The St. Matthew area fishery continued in 1978,
with a catch of 900 mt by 22 vessels, and in 1979,
when some blue king crab were taken as far north
as St. Lawrence Island. Interest in the 1979 fishery
was low, however, and only 96 mt were landed by
17 vessels. Typically, blue king crabs in the Northern
district are smaller (average 1.8 kg) than those taken
in the Pribilof Islands (3.5 kg).
Catches given above for the Norton Sound and
St. Matthew fisheries actually include all red and blue
king crab taken in the Northern district of the Bering
Sea. Since virtually all red king crab come from
Norton Sound and almost all blue king crab from the
St. Matthew area, this discrepancy is minor. Com-
mercial king crab fisheries in the Northern district
are small, recent in origin, and unlikely to become
more important than they are at present.
FOREIGN FISHERIES
Extent of the fisheries
Japan and the U.S.S.R. were the only foreign
nations that engaged in directed fisheries for king
1046 Fisheries biology
TABLE 61-4
All-nation effort in tiie eastern Bering Sea
king crab fishery, 1953-79.'
1,000's of lifts
Japan^
U.S.S.R.
U.S.^
Year
Tangle nets^
Pot^
Tangle nets
Pot
1953
106.3
—
—
—
1954
60.5
—
—
—
1955
99.2
—
—
—
1956
147.1
—
—
—
1957
83.6
—
—
—
1958
98.7
—
—
—
1959
78.4
—
64.0
—
1960
93.1
—
191.6
—
1961
256.7
—
388.0
—
1962
437.0
—
419.7
• —
1963
642.4
—
536.1
—
1964
638.9
—
607.5
—
1965
452.2
—
618.7
—
1966
447.3
—
617.2
2.7
1967
440.5
-
657.0
10.6
1968
484.7
151.6
241.0
47.5
1969
471.9
615.1
248.1
98.4
1970
252.3
797.1
228.9
96.7
1971
27.5
1,111.0
190.0
118.5
1972
12.1
1,104.1
—
205.1
1973
—
1,023.2
—
194.1
1974
—
852.2
—
258.4
1975
—
—
—
221.4
1976
—
—
—
390.4
1977
—
—
—
534.3
1978
—
—
—
507.3
1979
—
—
—
398.7
'From INPFC statistical yearbooks and ADF&G (1980).
^ Trawl effort is ignored. Data includes effort directed at
both red and blue king crab in the Pribilof and Southeastern
districts.
^Tangle-net effort in tan lifts (a tan is about 40 m of tangle
net).
■^Pot effort is for both king and Tanner crab fisheries since
separate statistics are unavailable. No foreign fishing since
1974.
crabs in the eastern Bering Sea. Foreign fleets ex-
ploited both the southeast Bering Sea red king crab
and, to a lesser extent, the Pribilof Islands blue king
crab stocks. After exploratory efforts in the 1930's,
Japan re-entered the fishery in 1953 and continued
fishing until 1974. The Soviet Union entered the
fishery in 1959 and competed with Japan and later
with the United States until 1971.
Before 1964 there was no international regulation
of foreign crab fisheries in the eastern Bering Sea.
The Japanese maintained a self-imposed size limit of
130 mm carapace width on male king crabs from
1955 to 1963. In 1964, the United States ratified
the Convention of the Continental Shelf (29 April
1958) and designated king and Tanner crab as
"Creatures of the Continental Shelf." This action
provided the rationale for U.S. management of
eastern Bering Sea crab fisheries. In that same year,
bilateral agreements were concluded with Japan and
the U.S.S.R. in which quotas and a minimum size
limit of 158 mm carapace width were applied to their
king crab catches. In addition, only hard-shell male
crab could be retained. Quota, area, and other
restrictions resulting from bilateral negotiations are
given in Table 61-5. Fishing areas are described
below in the section on foreign Tanner crab fisheries.
Foreign fishing for king crab is prohibited under the
Preliminary Fishery Management Plan for King and
Tanner Crab (U.S. Department of Commerce 1977).
The Japanese king crab catch in the eastern Bering
Sea in 1953 was 1,276,000 crab weighing approxi-
mately 25,100 mt. Japanese landings were less than
4,500 mt through the remainder of the 1950 's and
reached about 6,300 mt in 1960 (Table 61-3). With
TABLE 61-5
Quotas established under bilateral crab agreements
with Japan and the U.S.S.R.'
Years
1965-66
1967-68
1969-70
1971-72
Japan
U.S.S.R.
King crab
King crab
(Cases)^
(Cases)
185,000
185,000
163,000
100,000
85,000
53,000
37,500
23,000
(Number of crabs) (Number of crabs)^
1973-74 (Area A)
1973-74 (Area B)
270,000
430,000
100,000
160,000
(Metric tons)**
(Metric tons)
1975-76 (Area A)
1975-76 (Area B)
0
953
0
256
'Source: Environmental Impact Statement/Preliminary
Fisheries Management Plan. King and Tanner Crabs of the
Eastern Bering Sea (U.S. Dep. of Commerce 1977).
■^ One case is equal to 48 half-pound cans. In producing frozen
meat Japan considers 29.3 pounds of crab meat equivalent to
one case. For the years 1965-72 an average of about 24 crabs
was required for a case.
^The Soviets ceased fishing in 1971 despite the existence of a
quota.
^ There was no Japanese fishery in these years despite exist-
ence of a quota.
Crab fisheries 1047
the exception of 1960 and 1961, Japan took most
of the annual landings every year until 1971 (Fig.
61-8). Japan's catch peaked in 1964 with 5.9
million crab weighing 18,600 mt. A steady decline in
Japamese landings followed, and by 1970 the Japan-
ese catch had declined to 28 percent of the 1964
peak catch. Starting in 1965, blue king crab from the
Pribilof population made up 3-48 percent of the
Japanese king crab catch annually. Japanese catches
continued to decline from 1970 on until Japan
stopped fishing in 1974.
The U.S.S.R. entered the fishery in 1959 with a
catch of 620,000 crab weighing about 1,000 mt.
The Soviet fishery expanded rapidly (Table 61-3)
and peaked in 1961 with a catch of 10,200 mt.
In 1960 and 1961, the Soviet catch actually exceeded
that of the Japanese by a small number, although the
weight of the Soviet catch was somewhat less (Table
61-3). The Soviets landed more than 6,100 mt in
each succeeding year until 1966. The Soviet catch
was 3,800 mt in 1967 and only 800 mt by 1970. The
Soviets did not continue their fishery after 1971.
Equipment and effort
In the early years (Miyahara 1954), the Japanese
fishery employed factory ships (approximately 122 m
or 5,000 tons), trawlers (27 m or 60 tons) and
tangle-net-hauling boats (13.5 m). A tangle net is
simply a large mesh (approximately 23 cm bzir-
measure) bottom gillnet. The standard unit of gear
was the "tan," which was about 40 m in length. Net
hauling boats were also called "kawasaki" boats and
were carried aboard the factoryships (motherships).
Trawlers were used to scout for concentrations of
crab and set tangle nets, as well as for fishing. Some
danish seines were also used, but the method was
KING CRAB
100
90
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80
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70
Japan
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U.S.
\
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65 66 67 68 69 70 71 72 73 74 75 76 77 78 79
YEAR
Figure 61-8 Percentage of eastern Bering Sea king crab
landings taken by various nations.
abandoned when it proved ineffective. Aside from
the gradual substitution of synthetic twine for
cotton in tangle nets, methods remained much the
same until pot fishing began in 1968. Japanese pot
fishing is described in the discussion of Tanner crab
fisheries below. The Soviet fishery was similar to
the Japanese fishery in that one mothership served
a number of tangle-net-hauling boats.
In 1953, Japan reported (INPFC 1958) one mother-
ship, six tangle -net-hauling boats, and two trawlers
engaged in harvesting king crab in the eastern Bering
Sea. Efforts were reported as 106,345 tan hauls and
2,534 trawl hauls. By 1960, one mothership and 12
tangle-net-hauling vessels were fishing, and trawlers
were no longer involved in a directed fishery. Japa-
nese effort peaked at 642,450 tan lifts in 1963, then
declined to 452,160 tan lifts in 1965. The Japanese
began fishing pots in 1968 with an effort of 151,600
pot lifts. By 1970, pot fishing had expanded to
797,148 pot lifts, and their tangle-net effort had
declined to 252,320 tan lifts. In 1971 pots (1,111,020
lifts) virtually replaced tangle nets (27,543 lifts). The
tangle-net fishery was discontinued in 1972 but pot
effort remained near one million lifts until the
Japanese king crab fishery ended after the 1974
season.
A single set of effort statistics was used for Japa-
nese king and Tanner fisheries; most of the effort
in the 1970's was directed at Tanner crab. King crab
catches from 1973 onward were largely incidental to
Tanner crab fishing, and the negotiated quota in later
years (although not used) was designed to allow for
some incidental catch.
In 1959, the Soviet fleet consisted of one factory-
ship servicing eight catcher vessels. Effort consisted
of 64,000 tan lifts. Soviet effort more than tripled
by 1960 and reached 419,700 tan Ufts in 1962.
Effort continued upwards £ind reached a peak of
657,000 tan Ufts in 1967. The U.S.S.R. abruptly
de-emphasized king crab fishing in 1968; only 241,000
tan lifts were reported. Soviet effort remained low
until their fishing ceased in 1972 (Table 61-4).
ABUNDANCE OF KING CRAB
The abundance of king crab stocks has been
ascertained both from catch per unit effort (CPUE)
statistics (Fig. 61-9) and from trawl surveys designed
to provide an independent assessment of abundance
and distribution. Catch and effort statistics have
been monitored since 1953 and standardized trawl
surveys have been conducted continuously since
1969.
The time series of CPUE statistics (Fig. 61-9)
indicates that southeastern Bering Sea red king
1048 Fisheries biology
16
h
14
; \ JAPAN
12
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54 56 58 60 62 64 66 68 70 72 74 76 78
YEAR
Figure 61-9. Catch per unit effort in eastern Bering Sea
red king crab fisheries south of 58° (see text for explana-
tion of gear types).
crab were at moderate levels of abundance in 1953,
increasing through the 1950's; catch rates peaked in
1959. Both Japanese and Soviet fisheries enjoyed
high catch rates in 1959 and 1960. CPUE peaked
before the record foreign catches of the early 1960's.
It is difficult to determine whether the declining
catch rates of the early 1960's were due entirely to
declining abundance or partly to increasing competi-
tion between units of gear. Effort in both Soviet
and Japanese fisheries increased more than eight-
fold from 1959 to 1962, and catches continued to
rise. The average size of crab taken in the Japanese
fishery was stable from 1956 to 1962; it ranged from
158.0 to 158.9 mm carapace length (or approxi-
mately 3.3 kg). Both CPUE and average size gener-
ally decreased from 1964 to 1967 despite relatively
stable levels of effort. In 1967 the average size
reached 153 mm carapace length (approximately
2.9 kg).
Catch rates in the U.S. fishery from 1966 to 1970
declined precipitously, and by 1970 the catch rates of
all three nations reached all-time lows. Effort levels in
the U.S. fishery were increasing during this period
while those of foreign fisheries were declining. It is
worth noting that Pribilof Islands blue king crab
formed part of the Japanese catch from 1966 to 1970
(particularly in 1969). Separate effort statistics are
unavailable, and CPUE trends are shown (Fig. 61-9)
for a combined fishery. Since blue king crab catches
were small, trends in CPUE generally reflect stock
conditions for southeast Bering Sea red king crab.
The average size of red king crab taken by both U.S.
and Japanese fisheries declined significantly from
1967 to 1970. Those taken by the United States fell
from 3.5 kg in 1967 to 2.3 kg in 1970, in spite of
similar regulations concerning legal size during the
period (Table 61-2). The general trend toward
declining CPUE and average size was weU documented
(Hoopes and Greenough 1970), and by 1970 there
was multinational agreement that abundance was at
an all-time low.
The National Marine Fisheries Service trawl survey
is also used to provide information on distribution
and abundance of crab resources. The areas covered
by recent surveys are showm in Fig. 61-10; coverage
was similar from 1974 to 1977, but has expanded in
each succeeding year. Before 1974 the survey was
confined to the portion of the 1977 area south and
east of the Pribilof Islands. In 1979, sampling inten-
sity was doubled in the 1974-77 portion of the area
in order to increase precision in estimating popula-
tions of legal-sized crab (Otto et al., in press).
Population estimates (Table 61-6 and Fig. 61-11)
are obtained using a combination of the area swept
technique (Alverson and Percy ra 1969) and stratified
random-sampling techniques (Cochran 1963). Strati-
fication is based on the density of crabs of each
species. Estimates of the density of crabs per samp-
ling station are made by calculating the number of
crabs caught per square nautical mile (3.43 sq. km).
Estimated stock size is obtained by computing the
stratified average number of crabs per unit area and
multiplying by the area of crab habitat (by species)
within the survey area.
In general, trends in stock abundance of south-
east Bering Sea red king crab derived from the trawl
survey (Fig. 61-11) agree with those derived from
fishery data (Fig. 61-9). Apparently, the population
of legal-sized crab reached a low in 1970 and has been
increasing ever since. Estimates of the total popula-
tion (Table 61-6) of red king crab also show a general
increase from 1970 to 1977 but a slight decrease
since 1977. While this apparent decrease is not
statistically significant, other lines of evidence indi-
cate that a decrease in abundance of legal-sized crab
is to be expected in the near future.
Examination of the size-frequency distribution of
male red king crabs taken in the 1979 survey (Fig.
6 1-1 2a) shows a large modal group that peaks at
approximately 135 mm carapace length. This length
corresponds to the size at recruitment to the fishery
(ADF&G sampling shows that only 1.2 percent of the
catch was actually smaller than 135 mm in 1979).
Most of the left-hand side of this modal group is
within 16 mm (average annual molting increment:
Weber and Miyahara 1962) of the peak. The annual
probability of molting in this size-group ranges from
0.69 to 0.83, and natural mortality is about 10
percent per year (Balsiger 1976). It is hence expected
that the majority of crabs in the 120-134 mm size-
group will be available to the 1980 fishery. Of those
Figure 61-10. Areas covered by recent National Marine Fisheries Service trawl surveys of the eastern Bering Sea.
1049
1050 Fisheries biology
that do not molt in 1980, most of the survivors
will enter the 1981 fishery. The estimated number
of crabs in the range of 120-134 mm in 1979 is
comparable to that in 1978 (Table 61-6), and hence
the 1980 catch can be expected to remain high. The
effects of declining recruitment, evident from the
relatively flat size-frequency from 80 to 110 mm
(Fig. 61-12a), will probably be felt in 1981 and begin
to have substantial effects on the fishery in 1982.
Data for the Pribilof Islands blue king crab fishery
are sparse before 1973. The Japanese catch in 1973
was taken incidentally to Tanner crab fishing. Do-
mestic effort was minimal (6,800 pot lifts) in 1973,
the catch was small (580 mt), and U.S. CPUE was
25.6 crabs per pot lift. U.S. effort increased to
45,500 pot lifts in 1974 and decreased to 16,300 in
1975. There was a similar fluctuation in the catch
(Table 61-3 and Fig. 61-6). CPUE in 1974 (19.9
crabs per pot) and 1975 (19.3 crabs per pot) was
stable. Starting in 1976, U.S. effort in the Pribilof
Islands increased substantially, reaching 64,400 pot
lifts in 1976, 78,300 in 1977, and 101,200 in 1978.
Catches were, however, stable during this period and
averaged 2,900 mt. CPUE fell from 19.3 crabs per
pot in 1975 to 12.1 in 1976, 10.0 in 1977, and a low
of 8.0 in 1978. In 1979, 83,500 pot lifts yielded
3,450 mt and CPUE was 9.0 crabs per pot. There has
been no discernible trend in the average weight of
crab taken in the Pribilof Islands fishery. From 1974
to 1979 average weights ranged from 3.5 to 3.6 kg.
In general, trends in the U.S. fishery for Pribilof
Islands blue king crab indicate increased effort and
stable catch with declining CPUE. Declines in CPUE
have not been extreme in the past four years; perhaps
they simply reflect increased competition for a
constant stock. The NMFS trawl survey estimates
have fluctuated considerably from year to year
(Table 61-6). Fluctuations are probably related to
sampling error, since fewer than 20 survey stations
were contained within the habitat of the stock in
most years. When sampling error is taken into
account, the abundance of legal-size crab appears
stable. Examination of the 1979 length-frequency
distribution does not shed any light on future abun-
dance (Fig. 61-12b). Information on natural mortal-
ity, molting frequency, and incremental growth is
also lacking.
Fisheries for red and blue king crab in the North-
em district are too new to judge trends in abundance
from fishery -derived data. Since survey estimates
of abundance are also few and separated by several
years, no assessment of abundance is presented for
these stocks. Lechner and Tate (1979), Lechner
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Crab fisheries 1 051
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CRAB
/
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■
69 70 71 72 73 74 75 76 77 78 79
YEAR
Figure 61-11. Population estimates of male king crab,
>135 mm carapace length, derived from trawl surveys.
(1979), and Eaton (1980) provide descriptions of
fisheries for Northern district stocks.
TANNER (SNOW) CRAB STOCKS
Four species of Tanner (snow) crab are known in
the eastern Bering Sea. Chionoecetes bairdi and C.
opilio are widely distributed and are exploited by
commercial fisheries. C. angulatus and C. tanneri are
not fished in U.S. waters, but have been found in
deep water along the continental slope of the eastern
Bering Sea during trawl surveys. In addition, C. bairdi
and C. opilio hybridize in the eastern Bering Sea,
making up a very small percentage (<1 percent) of
Tanner crab stocks (Otto et al., in press).
Throughout most of their histories, either foreign
Tanner crab fisheries have been conducted indis-
criminately for C. bairdi and C. opilio, or those
concerned with tabulation of fishery statistics were
content simply to refer to the catch in aggregate.
The size of crab taken was probably more important
than its species in determining whether it was landed
and processed. Because species composition of
1052 Fisheries biology
A
245
-
rA .
210
-
r I Crab
175
-
f \
140
A
h
105
1 \
^^ \
70
I \ r
W \
35
, , , ,V
1-2 41-42 81-82 121-122 161-162
21-22 61-62 101-102 141-142 181-182
CARAPACE LENGTH (MM)
Figure 61-12a. Size-frequency distributions of red king
crab from the 1979 survey. Size at recruitment is approxi-
mately 135 mm.
BLUE
KING CRAB
21-22 61-62 101-102 141-142 181-182
41-42 81-82 121-122 161162
CARAPACE LENGTH(MM)
Figure 61-12b. Size-frequency distributions of blue king
crab from the 1979 survey. Size at recruitment is approxi-
mately 135 mm.
commercial catch was unknown and biologists were
not interested in Tanner crab during early explora-
tory cruises for king crab, it was many years before
the distributions of C. bairdi and C. opilio in the
eastern Bering Sea were fully documented.
Although 1974 surveys by Japan, the Soviet
Union, £ind the United States covered most of the
range of C. bairdi in the eastern Bering Sea (Fig.
61-13), it was 1975 before the entire range was
known as a result of the 1975 survey by the Outer
Continental Shelf Environmental Assessment Pro-
gram (Pereyra et al. 1976). It remained for the
1976 OCSEAP survey of Norton Sound and the
Chukchi Sea to document the northern extension of
C. opilio in the eastern Bering Sea (Wolotira et al.
1977). The probable range of C. opilio in the eastern
Bering Sea (Fig. 61-14) has not been surveyed in any
one year, and the distribution of C. opilio in the
Figure 61-13. Distribution of the Tanner crab (Chionoe-
cetes bairdi) in the eastern Bering Sea. Darkly shaded
portions indicate areas of consistently high abundance.
St. Lawrence Island area is still a matter of some
speculation.
The distribution of C. bairdi is strongly associated
with the coast of the Alaska Peninsula, continental
slope areas, and the Pribilof Islands (Fig. 61-13).
Surveys have mapped two centers of abundance in
most years. Most of the population has generally
been found in the area north of the Alaska Peninsula;
another area of concentration has centered on the
Pribilof Islands. The two centers of abundance
are connected by a region where C. bairdi, although
lower in abundance, is certainly not rare. Surveys
from 1974 onward showed that the size-frequency
distributions of C. bairdi in the Pribilof Islands
were different from those in the Eirea north of the
Peninsula. As NMFS surveys were expanded, it be-
came evident that crabs in the Pribilof area were
similar in size to those along the continental slope
north and west of the islands. More recently,
Somerton (1980) has shown differences in the appar-
ent size at sexual maturity between populations
east and west of 167°W longitude.
In summziry, there appear to be biological differ-
ences between C. bairdi populations in the Pribilof
Islands area and in the southeastern Bering Sea;
Crab fisheries 1 053
Figure 61-14. Distribution of the Tanner crab (Chionoe-
cetes opilio) in tiie eastern Bering Sea. Darkly shaded
portions indicate areas of consistently high abundance.
however, it is not yet clear whether these differences
are caused by genetic or environmental factors.
Nevertheless, C. bairdi in the eastern Bering Sea has
been considered a single stock for management
purposes.
From the distribution of various size-groups of
males and females in 1979 (Otto et al. in press),
it appears that large male and female C. opilio are
found on the southern and southwestern fringes of
the habitat (Fig. 61-14) and that juveniles are con-
centrated in northern and central areas. It may be
that C. opilio found north of St. Lawrence Island
are not self-sustaining. For example, data contained
in Wolotira et al. (1977) show that only 2.4 percent
of 7,061 females examined were carrying eggs in
Norton Sound and the Chukchi Sea. The scarcity of
egg-bearing females in the Norton Sound area was
also observed in 1979. Elsewhere in the Bering Sea,
the mean size at which 50 percent of the female
population is ovigerous was between 42 and 50 mm
carapace width (Somerton 1975, Macintosh et al.
1979). Wolotira et al. (1977) found that only 3.5
percent of 1,397 females of CEirapace width larger
than 50 mm were carrying eggs. Concentrations of
large males are found in widely differing localities
from year to year. For example, Pereyra et al. (1976)
found that large male C. opilio (>110 mm carapace
width) were about evenly distributed north and south
of 58°N latitude in 1975, but 1979 data showed only
6 percent of this size group north of 58°.
It seems probable that there is one extremely
large population of C. opilio in the eastern Bering
Sea, displaying localized areas of abundance that are
geographically unstable with time. For the purpose
of fishery management, C. opilio in the eastern
Bering Sea are considered a single stock.
TANNER CRAB FISHERIES
Before 1965, Tanner crabs were taken incidentally
to king crab fishing. Some directed fishing by Japan
did, however, take place as early as 1954, according
to reports in INPFC statistical yearbooks. Effort
was small and few catch data were given. Directed
Tanner crab fishing started after 1964, when bilateral
negotiations led to progressively smaller Japanese
and Soviet king crab quotas. The United States
entered the fishery in 1968, but fishing was incidental
to king crabbing until 1974. The U.S.S.R. discon-
tinued its fishery after 1971, but Japan's fishery has
continued to the present time. Until 1978 the
U.S. fishery was almost entirely for C. bairdi. Since
that time both species have been taken, although
C bairdi still provides most of the U.S. catch. Be-
cause of area restrictions on Japanese operations,
most of their current catch consists of C. opilio.
Domestic fisheries
Since most Tanner crab vessels also fish for king
crab, the general characteristics of vessels and gear
given above are equally representative of both fisher-
ies. The fishery for C. bairdi is conducted north of
the Alaska Peninsula and near the Pribilof Islands
from January to June. Much of the harvest of
C. opilio, until recently captured incidental to C.
bairdi, is also taken in this area. Most directed
U.S. fishing for C. opilio occurs east of the Pribilof
Islands during the summer months, although some
directed fishing also occurs near Amak Island.
Domestic fisheries were managed by the ADF&G
before 1978, when the North Pacific Fishery Manage-
ment Council's management plan went into effect
and the first federal regulations were promulgated.
The federal regulations do not differ substantially
from those of the State of Alaska, and management
of Tanner crab fisheries is currently a joint effort.
The evolution of regulations concerning Tanner crab
1054 Fisheries biology
fishing in the eastern Bering Sea is shown in Table
61-7. The purposes of regulations are the same as
those for king crab. Statistical areas are also the
same, although they are referred to as subdistricts
rather than districts.
Domestic tanner crab landings in the eastern
Bering Sea were less than 460 mt annually from 1968
to 1973. Some 482,000 crab were taken in the peak
year of this period (Table 61-8). After a directed
fishery was begun, C. bairdi catches grew rapidly
from 2,300 mt in 1974 to 10,100 mt in 1976 and
peaked at 30,020 mt in 1978. The 1979 catch was
much reduced and only 19,280 mt were taken. The
domestic C opilio fishery began in 1978 with a catch
of only 780 mt but grew rapidly to 14,600 mt in
1979 (ADF&G 1979b). Interest in C. opilio in 1979
was triggered by low production of C. bairdi. In
aggregate, U.S. landings of Tanner crab in the eastern
Bering Sea increased from 30,900 mt in 1978 to
33,900 mt in 1979. Fishermen were paid $0.52 per
pound for C. bairdi and $0.30 per pound for C.
opilio. The ex-vessel value of the 1979 catch was
$31.5 million. There is much interest in Tanner crab
fisheries; aggregate landings in 1980 will probably
remain high despite lowered prices ($0.21/pound)
for C. opilio.
Increased effort in the domestic Tanner crab fish-
ery paralleled increased catch. From 1968 to 1973
effort was sporadic and varied from 1,400 to 29,900
pot lifts (Table 61-8). Because of the incidental
nature of the fishery during these years, effort
statistics are difficult to interpret. Effort, expanding
rapidly since 1974 (22,000 pot lifts), reached a peak
of 508,000 pot lifts for C. bairdi and 13,900 pot
lifts for C. opilio in 1978. Effort in 1979 was 402,700
pot lifts for C. bairdi landings and 190,300 pot lifts
for C. opilio landings. The number of vessels engaged
in the Tanner crab fishery increased similarly from 18
in 1974 to 66 in 1976 and 119 in 1978. In 1979,
144 vessels reported landings of C. bairdi and 101
vessels landed C. opilio. Because some of their effort
was devoted to both species simultaneously, the
effort figures in Table 61-8 are somewhat inflated in
1978 and 1979. This difficulty with interpretation of
effort statistics also affects the abundance trends
discussed below.
Foreign fisheries
Soviet and Japanese mothership fisheries for
Tanner crab in the Bering Sea conducted operations
in a manner similar to those described for king crab.
In addition, in recent years a land-based (indepen-
dent) fleet of 10-17 Japanese crab vessels has oper-
ated in the portion of the eastern Bering Sea along
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1056 Fisheries biology
the continental shelf break adjacent to the U.S.-
U.S.S.R. convention line. Unfortunately, statistical
information from independent vessels is unavailable
before 1975. There has been some debate about the
degree to which the independent fleet was operating
in U.S. or Soviet waters before 1977.
Regulation of Japanese and Soviet Tanner crab
fisheries evolved parallel to those for king crab
under bilateral agreements. Modifications of the
quota areas (Fig. 61-15) have affected the species
composition of foreign, particularly Japanese, catches.
Mothership fisheries
The Japanese fished for Tanner crab to a limited
extent as early as 1953 and 1954. The reported
pack in 1953 and 1954 was 6,297 cases of half-
pound cans (Fisheries Agency of Japan 1956), or
about 3,150 cases per year. Fishing took place
"mainly off Amak Island." No information was
given concerning the number of crab caught in 1953
180'
175°
170'
1 65
160°
1 55
60'
55^^ -
T / 1 ^
!■
1
- / '" <!>%
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/
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1 80'
175'
170'
165° 160° 155'
and 1954. It seems probable that most of the catch
in this area was C. hairdi. The conversion factor
given in the 1970 INPFC statistical yearbook is 176
Tanner crab per case and the catch in 1970 was, by
all accounts, almost entirely C. hairdi. M the 1970
conversion factor is applied, the 1953-54 catch is
about 550,000 crabs per year. The reported catch
for 1965 was 1,030,000. From the limited data at
hand, annual Tanner crab production by the Japanese
mothership fleet was probably fewer than 1,000,000
crabs per year from 1953 to 1964. The average size
of C hairdi taken by the mothership fleet in later
years is less than 1.4 kg, and hence catches probably
did not exceed 1,400 mt before 1965.
The catch history of Japanese and Soviet Tanner
crab fisheries (Table 61-8, Fig. 61-16) shows rapid
development starting in 1967 after two years of
stable and perhaps incidental catch. The catch
history is presented in numbers of crabs in accord-
ance with INPFC records. Fishing effort was redi-
rected toward Tanner crab, at least in part, because of
180° 175° 170° 165° 160°
1 55'
^ -«^ A
19 75 ^ 19 76^'^^*--
- 55°
T — 7 ■
1 ^ 1
1
/
- /
'^^S^,
/
fe\i
'\
--.^
..--.- Fl SH 1 ^'^yrj^
1978
'
rz 60°
1 80° 175° 170°
165'
1 60'
1 55°
Figure 61-15. Quota areas for Japanese and Soviet crab fisiieries in the eastern Bering Sea. Areas from 1973 to 1976 were
negotiated through bilateral agreements; 1977 areas result from the Preliminary Management Plan for king and Tanner crab
fisheries, and the 1978 area is from the North Pacific Fishery Management Council fishery management plan for Tanner crab.
Crab fisheries 1057
65 66 67 68 69 70 71 72 73 74 75 76 77 78 79
YEAR
Figure 61-16. Catch histories of eastern Bering Sea
Tanner crab fisheries by various nations.
declining king crab quotas. With a greater emphasis
on Tanner crab, the CPUE in the Japanese tangle-net
fishery increased from 3.3 Tanner crab per tan lift
in 1966 to 18.9 crab per tan hft in 1967. Increases in
Soviet CPUE were also rapid. By 1969, CPUE in
both tangle-net fisheries had peaked (35.8 for Japan,
24.2 for the U.S.S.R.), and redirection could be
considered complete. Some reported effort was,
however, still directed at king crab. Japan relied on
expanding pot fisheries rather than simply redirecting
efforts with tangle nets. For example, the percentage
of the Japanese eastern Bering Sea Tanner crab catch
taken by tangle nets declined from almost 97 percent
in 1967 to 42 percent in 1969 and 5 percent in 1971.
In order to adjust for differences in the efficiencies
of different gear, the fishing power of each kind of
gear was computed relative to U.S. pot lifts according
to the method of Robson (1966). This procedure
makes it possible to compute the total effort of all
nations in eastern Bering Tanner crab fisheries.
Plotting of total effort against the estimated total
catch in weight (Fig. 61-17) shows that catch and
effort follow divergent trends until about 1969. From
1970 on, trends in catch and effort became progres-
sively more similar as foreign king crab fisheries were
phased out and as U.S. effort increased.
b
TANNER CRAB
100
-
90
-
^--
\ Effort
1
-
80
'
\
\
\ ^ -A
/
^^
\ -^ \
1
(0
O
70
-
\
\
f f
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1 1
X
\
/ /
■""^
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-
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-
(A
Q
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\
\
/ /
/ /
z
50
-
.. . V
/ /
-
3
/ Nv ^^-^
/ /
o
Q.
40
-
Catch / \^^
\
\
\
/ /
-
30
~
^X ^^^
^^^S
/ /
'
20
-
/
-
10
-
-
2700
T)
O
2400
H
r
2100
■n
H
m
1800
O
c
<
1500
>
r
m
1200
z
(0
^^^
900
X
•A
o
600
<0»
- 300
65 66 67
68
69 70 71 72 73 74 75 76 77 78
YEAR
Figure 61-17. All-nation catch and effort in eastern Bering Sea Tanner crab fisheries. Relative effort computed accord-
ing to the method of Robson (1966).
1058 Fisheries biology
The combined catch of foreign fleets peaked in
1969 and 1970 and declined somewhat in 1971.
Catches decUned further in 1972 when the U.S.S.R.
left the fishery. Tangle -net fishing was prohibited
starting in 1973 as a result of previous bilateral
negotiations. Foreign Tanner crab quotas have been
in existence since 1969. The all-nation catch reached
a low point in 1975 because of decreased quotas in
response to increasing U.S. interest and, perhaps, a
slight lag in U.S. fishery development. All-nation
catch has increased ever since, as a result of U.S.
development and some liberalization of Japanese
quotas from 1977 through 1979. Present regulations
call for a 50-percent reduction in the Japanese quota
in 1980.
Species composition data for Japanese catches of
eastern Bering Sea Tanner crab are generally lacking
before 1977, and there are no data for the Soviet
fishery. Three sources of data are available for
estimating the species composition of the Japanese
catch. Data provided to INPFC by the Fishery
Agency of Japan provide catch of Tanner crab and
effort (tans or pots) by one-degree squares for the
Japanese mothership fleet from 1970 to the present.
Combined with knowledge of the spatial distribution
of both species, the Japanese catch and effort data
provide an idea of relative species composition.
The Japanese have also provided length-frequency
data for both species from 1973 to the present in
the course of negotiations. Assuming that the Japan-
ese size-composition sampling data are representative
of the catch, an estimate of species composition was
possible. U.S. observer data are available from 1972
to the present, but before 1977 these data are incom-
plete to varying degrees. A synthesis of these data
sources (Table 61-9) shows that the importance of
TABLE 61-9
Estimated species composition of Japanese mothership catches of eastern Bering Sea Tanner crabs.'
Year
Area
Catch (1,000'sof crab)
C. bairdi C. opilio
Total
% C. opilio
1970
1971
1972
1973
1974
1975
1976
1977
1978
1979
A
B
Total
A
B
Total
A
B
Total
A
B
Total
A
B
Total
A
B
Total
A
B
Total
A
B
C
Total
S. of58°
N. of58°
Total
S. of58°
N. of 58°
Total
15,880
811
16,691
12,731
1,286
14,017
13,828
986
14,814
5,812
3,657
9,469
5,519
5,112
10,631
2,209
4,438
6,647
2,410
3,459
5,869
2,354
2,221
112
4,687
0
1,600
1,600
0
2,120
2,120
836
16,716
5
663
147
45
1,499
18,190
8
670
13,401
5
1,052
2,338
45
1,722
15,739
11
728
14,556
5
52
1,038
45
780
15,594
5
180
5,992
3
4,294
7,951
54
4,474
13,943
32
480
5,999
8
2,875
7,987
36
3,355
13,986
24
192
2,401
8
2,389
6,827
35
2,581
9,228
28
24
2,434
1
3,747
7,206
52
3,771
9,640
39
98
2,452
4
4,945
7,166
69
2,136
2,248
95
7,179
11,866
61
1,578
1,578
100
12,662
14,262
89
14,240
15,840
90
1,715
1,715
100
19,084
21,204
90
20,799
22,918
91
'Japanese catch sampling data used for species composition in 1970-76; U.S. observer data used thereafter.
Crab fisheries 1059
C. opilio in the mothership fleet catch has increased
from perhaps 10 percent (1970-71) to 90 percent
(1978-79). During the period from 1953 to 1969 the
mothership fleet was concentrated in the southeast-
em Bering Sea (Area A), and catches probably were
on the order of 5-10 percent C. opilio. Because of
similarities between Soviet and Japanese fishing
areas and operations, it is probable that the Soviet
catches were similar in composition to those of
Japan.
I suspect that using length-frequency sampling
data as a proxy for size composition of the catch
results in overestimating the contribution of C.
opilio to the catch before 1977. This could happen
if samples taken in order to characterize size compo-
sition contained a disproportionate number of C.
opilio. For this reason estimated catches by species
before 1974 are probably useful only for the purpose
of illustrating general trends. All accounts, however,
do agree that the trend was from predominance of C.
bairdi to predominance of C. opilio in Japanese
mothership catches, and that this shift was largely the
result of negotiated or regulated changes in fishing
areas (Fig. 61-15).
The two factoryships currently used by Japan to
process Tanner crab are the Keiko Maru (7,519 gt)
and Koyo Maru (7,500 gt). Both are about 137
m in length. The factoryships process crab from
four to seven catcher vessels that are about 27 m in
length (100 gt). Japanese crab fishermen use top-
loading pots in the shape of a truncated cone, fished
on a groundline. About 130 pots are fished per line,
with a three- or four -day soak. Each vessel has about
2,000 pots distributed among 15-18 strings of gear.
Gejir is hauled using a hydraulic longline puller
(gurdy). Crab are removed from pots and stored in
sacks in the fishhold. The catches are delivered daily
to the factoryship, obviating the need for tanks and
circulating pumps.
Japanese independent vessel fishery
The Japanese land-based fishery was conducted
in the area bounded by 55°30'N, the U.S.-U.S.S.R.
convention line, and 175°00'W (often called the
"triangle area") until 1978. Some land-based fishing
occurred east of 175° in 1979. The NMFS has no
data on this fishery before 1975. In most years, the
catch has come largely from grounds situated near
the 183-m isobath. Japan licensed 28 vessels to fish
in the triangle area in 1975 and 31 vessels in 1976
(Beardsley 1975 and 1976). The vessels are larger
(40-50 m) than the catcher vessels used in conjunc-
tion vdth mothership operations and process and
freeze their catch. The frozen product is periodically
transferred to a supply ship (freighter). Fishing
operations are similar to those described above.
Vessel effort has declined in the land-based fishery:
only 11 vessels were fishing in 1978 and 1979. In
1980, however, 17 independent vessels have been
licensed, perhaps in part because only one factory-
ship is operating in the eastern Bering Sea in 1980.
Before 1977, catches by the independent fleet
were not considered in estabhshing Japanese quotas,
and management of the fishery was conducted
entirely by Japan. Both quotas and fishing areas
have been adjusted by Japan within the framework
of regulations governing Japanese eastern Bering Sea
fisheries in 1977, 1978, and 1979.
Catch by the independent fleet increased from
2,919,000 crab or about 2,100 mt in 1975 to
4,462,000 crab or 3,300 mt in 1978 (Table 61-10).
The catch in 1979 was similar to that of 1978. The
average size of crab taken in the fishery has been
remarkably stable, ranging from 0.72 to 0.75 kg in
the last five years. The stability in average size could
be taken as implying stable species composition of
the catch. U.S. observers, however, estimated that 17
percent of the 1978 landed weight and 8 percent of
the 1979 landed weight consisted of C. bairdi. In-
formation provided by the Fishery Agency of Japan
TABLE 61-10
Fishery statistics from the Japanese independent vessel (land-based) fleet'
Catch
%C.
bairdi
Catch
per day
Vessels
Vessel days
mt
1,000's
mt
1,000's
mt
1,000's
1975
28
1,115
2,100
2,919
—
—
1.9
2.5
1976
31
1,477
2,109
2,929
—
—
1.4
2.0
1977
11
620
2,721
3,677
NA
1.5
4.4
6.2
1978
11
832
3,271
4,462
17.0
13.7
3.9
5.1
1979
11
1,026
3,200
4,273
8.0
8.0
3.1
4.2
* Provided by Japan during bilateral negotiations (1975-77); U.S. observer estimates (1978-79).
1060 Fisheries biology
indicates that, by numbers of crabs, the percentage of
C. bairdi in the independent fleet catch was 1.5 in
1977, 13.7 in 1978, and 8.0 percent (preliminary
estimate) in 1979. There is good agreement between
the two data sources in 1978 and 1979, but the
reported proportion of C. bairdi in the 1977 catch
seems low. There was some change in fishing areas
after 1977, and the 1977 data are based on length-
frequency data collections rather than direct catch
sampling. The species composition of the land-based
fleet's catch may not have been pairticularly stable,
but C. bairdi was probably on the order of 10 percent
in most years.
Because effort data in terms of pot-lifts are not
available for the land-based fleet for more than two
or three years, the number of vessel days fished is
used as an index to effort. Effort apparently de-
creased abruptly from 1975 and 1976, when well
over 1,000 vessel days were reported by Japan, to
only 620 vessel days in 1977 (Table 61-10), reported
by U.S. observers. This decline was occasioned by a
29 percent increase in catch and a decrease of 35-40
percent in the number of vessels licensed by Japan.
Since 1977, data from U.S. observers suggest that
catch and effort have been somewhat better corre-
lated. Trends in effort are explainable by the incep-
tion of a U.S. management regime coincident with a
decrease in the number of licenses granted, followed
by gradual increase in effort associated with liberal-
ized quotas.
The land-based fleet has been taking increasingly
larger crabs than the mothership fleet. For example,
the average sizes of Tanner crab in 1975 were 1.0 kg
(Area A) and 0.8 kg (Area B) for the mothership
fleet, and 0.7 kg for the land-based fleet. The land-
based fishery has taken larger crabs than the mother-
ship fishery each year since 1975. In 1979 the
average size taken by the mothership fleet was
0.63 kg, by the independent fleet 0.75 kg. Insofar
as large crab are more profitable than small crab, the
land-based fleet may have gained some advantage.
Economic advantages may have played some part
in stimulating effort in the land-based fishery in
spite of declining catch rates. On the other hand, the
declining abundance of crab may simply have meant
that more fishing was required to achieve the same
catch. In 1979, for example, the catch was slightly
smaller than that of 1978 despite a 23-percent
increase in effort.
ABUNDANCE OF TANNER CRAB
The earliest available index to the abundance of
Tanner crab is the catch rate in tangle nets set by
Japanese scout and commercial vessels from 1955
to 1965 (Fig. 61-18, Fisheries Agency of Japan
1967). Most of the scouting effort was directed
toward finding concentrations of red king crab.
Catch rates tended to be higher in the early 1960 's
than in the late 1950's. Tanner crab made up pro-
gressively larger portions of the catch by scout vessels
from 1956 to 1963. Since red king crab (the major
component of the catch) were also abundant during
this period, it is probable that Tanner crab (pri-
marily C. bairdi) were in high abundance during the
early 1960's. Starting in 1966, tangle-net catch rates
rose continually as a directed fishery was mounted
and peaked in 1969 (Fig. 61-19). While some of the
rise in catch rates probably reflects increased interest
in Tanner crabs, it seems probable that moderate to
high populations of Tanner crab in the early 1960 's
were generally increasing through most of the decade
and declined somewhat in the early 1970's. Catch
rates in the Japanese pot fishery, however, remained
stable. Although fishing areas changed somewhat
during the period from 1955 to 1972, most of the
catch was probably C. bairdi. Catch rates in U.S.
trawl surveys (Fig. 61-20) corroborate the view that
the abundance of large C. bairdi was low in the early
1970's, even though the total catch remained high
(Fig. 61-16 and Table 61-8). Recent trawl survey
estimates (Fig. 61-21 and Table 61-11) and U.S. catch
rates show that the fishable stock of C. bairdi in-
creased from 1973 until 1975 and decreased precipi-
tously after 1975. The size-frequency distribution of
male C. bairdi (Fig. 61-22a) indicates that the abun-
dance of legal-sized (>134 mm) crab is not going to
rise in the near future, perhaps up to three years.
There is no information available for analysis of
population abundance trends in C. opilio before
1970. The NMFS trawl survey population estimates,
made in 1970 and 1972, were 13.2 and 33.1 million
large male crab (>110 mm carapace v^ridth). Much
of the difference between these estimates can be
attributed to differences in sampling area. Both
estimates are, however, substantially lower than the
1973 population estimate of 84.7 million large males.
Insofar as population estimates for large male C.
bairdi and C. opilio in the area south of 58° have
tended to be parallel (Fig. 61-21, Table 61-11), it
may be reasonable to suppose that both species were
at low levels in the early 1970's. Fisheries data
provide no additional insight since species-
composition data are not sufficiently detailed to
permit estimates of the CPUE by species. It is
apparent, however, that the importance of C. opilio
in the Japanese mothership fishery began to increase
dramatically in 1974 (Table 61-9) after the imposition
of quota areas that excluded Japanese vessels from C.
bairdi grounds (Fig. 61-15).
Crab fisheries 1061
Currently, U.S. and Japanese C. opilio fisheries
harvest crab greater than 100 mm in carapace width
(there is no legal size limit). The size-frequency
distribution of C. opilio (Fig. 61-22b) shows that
only a small portion of the stock is being harvested.
It seems likely that further development of C. opilio
fisheries will have little measurable effect on the
population. The abundance of C. opilio of fishable
size is also expected to remain stable, although
localized scarcities may develop as fisheries intensify.
In summary, it appears that C. bairdi populations
were at relatively high levels in the periods 1959-63,
1968-69, and 1974-76. Populations have declined
radically each year since 1975, a trend which is
apparent in both NMFS survey estimates and com-
mercial fishery catch rates. Available data are too
few to evaluate population trends of C. opilio before
1973. Populations of C. opilio have followed the
same trends as those of C. bairdi since 1973.
THE FUTURE
Another crab fishery is developing in the eastern
Bering Sea. Landings of Korean hair crab (Erimacrus
isenbeckii, also known as horse crab) were 4.5 mt in
1979, but had reached 13.6 mt in 1980 (as of
April 21). Landed value has been variable, but current
prices approach $0.75/lb. Survey estimates in 1979
indicated that about 5,700 mt could be harvested
if hair crab were exploited at the same rate as other
eastern Bering Sea crabs. About half of the available
resource was in the Pribilof District.
Korean hair crab and C. opilio Tanner crab are the
only short-term developmental prospects for eastern
Bering Sea crab fisheries. Fisheries for golden king
crab (Lithodes aequispina) may, however, be de-
veloped in the future if economic conditions allow.
Over the past three to five years, king crab and
C. bairdi Tanner crab have been the mainstay of
eastern Bering Sea crab fisheries. It now appears
that southeastern Bering Sea red king crab will be
declining in abundance in 1981 and 1982. Further-
more, the C. bairdi population is at a low ebb and
little recruitment seems to be coming to the fishery
over the next one to two years. In consequence,
eastern Bering Sea crab fisheries will be economically
less productive in the early 1980's than they have
been throughout the last half of the 1970's. The
problem of low abundance of the resource is com-
pounded by high fuel costs and interest rates, as
Chionoecetes sp.
61 63 65 67 55 57 59 61 63 65 67
YEAR YEAR
Figure 61-18. (a) Catch per unit effort by Japanese scouting vessels (points) and early commercial efforts (x's) in the
eastern Bering Sea; (b) proportion of Tanner crab in all crabs taken by scouting vessels.
1062 Fisheries biology
100
^
90
cc
O
80
§
70
a:
LU
Q.
60
QQ
<
50
GC
O
40
CC
LU
z
z
30
20
10
US POT
C. bairdi
^^ US POT
\ C. opilio
JAPAN TANGLE NET
USSR TANGLE NET
Area B
JAPAN POT
^^^ . J I North of
' Area A \\\ ^'^-
58'
South of 58'
^
65 66 67 68 69 70 71 72 73 74 75 76 77 78 79
Figure 61-19.
areas).
YEAR
Catch per unit effort in various national fisheries for Tanner crab in the eastern Bering Sea (see Fig. 61-15 for
cc
m
160-
140-
\
120-
\ C. bairdi
1
100-
\ (> 130 mm carapace width)
80-
\
60-
\
40-
V /
20^
^\~1 /
J
— ~y
1
1 1 1 1
1969
1970
1971
YEAR
1972
1973
Figure 61-20. Catch rate of large Tanner crab (C. bairdi)
in early U.S. trawl surveys (from Hayes and Reid 1975).
well as intense competition among individual vessels
of the now large fleet. The immense resource of
C. opilio Tanner crab offers an opportunity if suffi-
cient markets can be found. At present, however,
C. opilio have a landed value of only $0.20-0.22/lb,
compared to $0.52/lb for C. bairdi. Moreover, king
crab prices appear to be falling, perhaps in response
to recent record catches and prices. It is evident
that eastern Bering Sea crab fisheries are headed
toward leaner times unless new markets are de-
veloped on both domestic and international fronts.
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1063
1064 Fisheries biology
275
•
/\
/
\
250
1
\
\ TANNER CRAB
1
\
225
1
1
\
\
«I>N
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/ /
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25
73
74
75
76
YEAR
77
78
79
Figure 61-21. Abundance estimates for large Tanner
crabs (carapace widtiis: C. opilio >110 mm; C. bairdi
>129 mm) from recent National Marine Fisheries Service
trawl surveys (sizes correspond approximately to size at
recruitment).
C. bairdi
1-2 41-42 81-82 121-122 161-162 201-202
21-22 61-62 101-102 141-142 181-182
CARAPACE WIDTH (MM)
Figure 61-22a. Size-frequency distributions of C. bairdi
from the 1979 trawl survey.
C. opilio
41-42 81-82 121-122 161-162 201-202
21-22 61-62 101-102 141-142 181-182
CARAPACE WIDTH (MM)
Figure 61-22b. Size-frequency distributions of C. opilio
from the 1979 trawl survey.
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Alaska Department of Fish and Game
1978 Alaska shellfish commercial fishing
regulations. ADF&G, Juneau, Alaska.
1979a Alaska shellfish commercial fishing
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1979b Westward region Tanner crab report
to the Alaska Board of Fisheries.
ADF&G, Kodiak, Alaska.
1980 Westward region shellfish report to
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Alverson, D. L., and W. T. Pereyra
1969 Demersal fish explorations in the
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Balsiger, J. W.
1976
A computer simulation model for
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Beardsley, A. J.
1975 Observations of Japanese crab factory
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Crab fisheries 1065
1976 Observations of Japanese crab factory
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Cochran, W. G.
1963 Sampling techniques,
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John Wiley
Congressional Research Service
1974 Treaties and other international agree-
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Eaton, M. F.
1980
Status of the United States Tanner
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1949 Report of Alaska exploratory fishing
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1949
Lechner, J.
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1980 Regional variation in the size of
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1977 Final environmental impact state-
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eastern Bering Sea. NOAA/NMFS,
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Wallace, M. M.,. C. J. Pertuit, and A. R. Hvatum
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king crab Paralithodes camtschatica
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Serv. Fish. Leafl. 340.
Weber, D. D., and T. Miyahara
1962 Grovifth of the adult male king crab
Paralithodes camtschatica (Tilesius).
U.S. Fish Wildl. Serv. Fish. Bull.
62:53-75.
Wolotira, R. J., T. M. Sample, and M. Morin
1977 Demersal fish and shellfish resources
of Norton Sound, the southeastern
Chukchi Sea, and adjacent waters in
the baseline year 1976. Northwest
and Alaska Fish. Cent. Proc. Rep.
NOAA/NMFS.
Seetion Xll
Benthic Biology
Howard M. Feder, editor
Benthic Invertebrate Macrofauna
of the Eastern Bering/Chukchi Continental Shelf
Sam Stoker
Institute of Marine Science
University of Alaska
Fairbanks
ABSTRACT
This study presents a view of a closely interrelated
Bering/Chukchi benthic community system that extends
unbroken over the entire continental shelf, with the Chukchi
Sea benthos probably relying heavily on the Bering Sea for
both food supply and recruitment. Indications are that this is
a highly productive and relatively stable benthic system
composed of at least eight major faunal assemblages of con-
siderable complexity. The environmental factor correlating
most strongly with the distribution of these faunal assemblages
and with distribution of individual major species appears
to be sediment type, but summer bottom temperature and
water mass distribution may also be critical.
The distribution of standing-stock biomass in relation to
diversity suggests predation pressure on the southern and
northern extremes of the study area, presumably the result of
benthic-feeding marine mammal populations and possibly, in
the southern region, demersal fish.
In general, it appears to be a strongly detritus-based trophic
system, with a high standing-stock biomass observed in the
Bering Strait and southern Chukchi Sea region, probably the
combined result of high near-surface primary productivity
distributions and current structure.
The benthic fauna over this region appears to be dominated
by boreal Pacific forms, probably also a result of the current
structure, with high-arctic forms frequent only in the northern
waters.
INTRODUCTION
The continental shelf of the Bering and Chukchi
seas is one of the largest and probably one of the
richest in the world in faunal resources, supporting
numerous species of marine mammals and marine
birds as well as commercially important stocks
of finfish and invertebrates. In addition to such
renewable resources, there is a high probability that
this shelf contains significant nonrenewable mineral
resources, principally petroleum and heavy metals.
The development of these two sets of resources is not
necessarily incompatible. However, if mineral ex-
ploitation is to be undertaken without adversely
affecting the renewable resources, the harvest of
which is also presently expanding, an understanding
of the total ecosystem of the region must be achieved
in order to avoid undue perturbations.
This chapter will attempt to shed some light on one
part of that ecosystem, the distribution and ecology
of the benthic infauna of the continental shelf. This
benthic infauna not only constitutes a potential
commercial resource in its own right but also provides
critical food resources for many of the demersal fish,
epibenthic invertebrates, marine mammals, and
marine bird species which inhabit the region.
Most of this chapter is based on results of a recent
study of the benthos of the Bering/Chukchi shelf
(Stoker 1978). The principal objectives of this study
were (1) to determine the quantitative and qualitative
distributions of benthic invertebrate macrofauna over
the eastern continental shelf of the Bering and
Chukchi seas and to correlate distributions with
depth, sediment type, latitude, and longitude, (2) to
define faunal assemblages and to correlate the dis-
tribution of such assemblages with environmentzil
conditions, and (3) to evaluate, insofar as possible,
seasonal and annual fluctuations of the benthic
standing stock.
DESCRIPTION OF STUDY AREA
The continental shelf of the Bering and Chukchi
seas totals about 1,595,500 km" . Almost two-thirds
of this area (1,015,500 km^ ) lies in the Bering Sea
(Lisitsyn 1969), the remaining 580,000 km^ in the
Chukchi (Ingham and Rutland 1970). About 45
percent of the Bering Sea and all of the Chukchi
Sea lie on this continental shelf. The physical and
biological processes of the two are closely inter-
related.
1069
1070 Benthic biology
The region sampled quantitatively under this study
comprises most of the continental shelf of the Bering
and Chukchi seas east of the Convention Line of
1867 and from about 56° N to 73°N, a total area of
roughly 1,000,000 km' (Fig. 62-1).
PREVIOUS INVESTIGATIONS
Much more information is available concerning the
benthos of the Bering Sea than of the Chukchi Sea,
but even for the Bering Sea large gaps in knowledge
are apparent.
Studies of the Bering Sea shelf have described the
faunal assemblages in two ways, by feeding (trophic)
type (Kuznetsov 1964), and by dominant species
(Filatova and Barsanova 1964; Zenkevitch 1963;
Neiman 1960, 1963; Rowland 1973; Stoker 1973).
In all descriptions of faunal assemblages by dominant
species, major elements of more than one trophic
type are found, although generally one trophic type is
numerically dominant within these assemblages.
From a review of the available literature, it appears
that several physical factors may influence the
qualitative and quantitative distribution of Bering Sea
benthic fauna. These include sediment particle size,
bottom temperature, depth, sedimentation rates,
circulation intensity, and suspended particulate
content of the near-bottom water. Although it does
appear possible to predict in a general sense the
faunal composition and abundance of an area from
descriptions of sediment particle size, bottom tem-
perature, and depth (Neiman 1960), it is difficult or
impossible, given the data available, to define the
exact relationships between these factors and such
biological distributions.
Unfortunately, no detailed information is currently
available regarding the benthic fauna of the Chukchi
shelf. Such qualitative and semi-quantitative studies
as have been undertaken in the southeastern Chukchi
(Sparks and Pereyra 1966, Zenkevitch 1963) indicate
that, although more arctic species are represented
here than in the Bering Sea, the benthic fauna is
primarily boreal Pacific in origin. It is conjectured
(Sparks and Pereyra 1966) that low bottom tempera-
tures in this area may preclude in situ reproduction of
many of the major species and that these species
depend for recruitment on larvae swept north from
the Bering Sea.
METHODS
Field collection
The field sampling for this study spanned a four-
year period, from 1970 through 1974, and included
both summer and winter collections.
At each quantitative station, five samples were
taken with a weighted 0.1 -m' van Veen grab. It was
determined from a previous assessment of results
(Stoker 1973) that five replicate samples were enough
to maintain statistically valid station descriptions in
that within -station sample variance was consistently
less than variance between stations (based on presence/
absence and relative abundance of species). In all, a
total of 176 quantitative and 33 nonquantitative
stations were established (Fig. 62-1). Nonquantita-
tive stations were sampled with a 3-m otter trawl.
Since such trawl samples were primarily epifaunal
rather than infaunal in character, they are not in-
cluded in the distributional analyses.
Once on board, each quantitative sample was
washed and screened through 3-mm and 1-mm sieves.
Coarse (3-mm) and fine (1-mm) faunal fractions were
preserved separately in 10-percent buffered forma-
lin for return to the laboratory. At stations where
very cozirse sediments were encountered, only the
3-mm faunal fraction was retained. At each station, a
sediment sample was obtained, also using the van
Veen, and frozen for later analysis. Organisms of
representative species were collected from the non-
quantitative samples and frozen so that comparative
values of organic carbon, nitrogen, and caloric con-
tent could be obtained for frozen versus formalin-
preserved samples.
It must be pointed out that at none of the stations
sampled was it feasible, given time limitations or ice
conditions, or both, to anchor the ship. Although
efforts were made to hold position as closely as
possible, the five replicates comprising a station may
in fact be spread over quite a large area. This is
particularly true of winter stations, where rapid
drifting of pack ice frequently resulted in a transect a
mile or more in length.
A more serious flaw was the inability of the grabs,
or trawl, to sample the populations of large, deep-
burrowing bivalves of the genera My a and Spisula.
These bivalves are known to make up a large part of
the diet of the Pacific walrus in the northern Bering
Sea and Bering Strait region (Fay et al. 1978), but are
rarely obtained in samples from this area. When they
are caught by the grab, generally only part of the
severed siphon is retained. This problem has plagued
other investigators in the past (Lukshenas 1968, Ellis
1960), and could not be overcome at this time
because of severe limitations of the ship and gear. It
seems probable, from the evidence of the walrus
stomachs, that these large bivalves may constitute a
considerable percentage of the benthic standing stock
over the study area; precisely what percentage
is impossible to estimate at this time.
175'
180'
175'
1—
170'
165'
160'
155'
1—
^'V
201
70'
65'
60" -
55" -
175'
BERING SEA
Benthic Stations Occupied i970^
• Quantitative Stations
^ Qualitative Stations
180'
175
170" 165" 160"
Figure 62-1. Benthic stations occupied on the Bering/Chukchi continental shelf.
1011
155'
1072 Benthic biology
Laboratory analysis
In the laboratory, the faunal samples were sorted
and identified as to phylum, class, genus, and species,
and the number of individuals and total wet weight of
each species in each quantitative sample were re-
corded. Because of time limitations and the appar-
ently negligible biomass of the fine (1-mm) fractions,
only one representative fine-fraction sample of the
five collected was processed, for comparative pur-
poses, for most of the stations. All of the coarse
fractions were processed.
Representative samples of each major species were
analyzed for organic carbon and nitrogen content
using a Perkin-Elmer model 240 CHN Microanalyzer
and for caloric content using a model 1221 Parr
Oxygen Bomb Calorimeter. These values were then
related to total wet weight for each species. For
minor species not analyzed, values were extrapolated
from the closest related taxon which was analyzed.
One sediment sample from each quantitative
station was sieved through a series of standard sedi-
ment screens to obtain coarse-fraction particle-size
percentages; remaining fine fractions were then
subjected to standard pipette analysis to obtain
fine-fraction particle-size percentages. Sediment
mean and mode particle sizes are described by phi
value (negative log to the base 2 of particle diameter
in millimeters).
Data processing
When the laboratory analysis was finished, result-
ing sample data were coded for incorporation in
computer listing and analysis programs. All quantita-
tive values were related to one square-meter area. For
each station, the Brillouin index of diversity (Pielou
1969) was calculated and listed, based on the coarse
(3 -mm) sieve fraction results.
Next, all species were ranked according to their
contributing percentage of total mean population
density and organic carbon biomass averaged over the
total area. Those species comprising, cumulatively,
95 percent of either density or organic carbon bio-
mass were selected as indicator (dominant) species to
be included in subsequent statistical analyses. Rare
species (fewer than four station occurrences), organ-
isms unidentifiable to species level, and species of
questionable taxonomic certainty were excluded
from this list. This ranking and listing was performed
separately for both coarse and fine sieve fractions.
Using the quantitative results pertaining to these
selected indicator species, a station cluster analysis
was performed in order to group stations according to
faunal similarities. This program clustered stations on
the basis of similarities in relative (percent) species
composition, applying the formula;
C=E^ [2W/(A+B)],
i
where C = affinity coefficient, A = percentage
density of species i-e at Station A, B = percentage
density of species i-e at Station B, and W = the
lesser percentage value of species i-e at either Station
AorB.
Species i-e = species occurring at either Station A
or B. The use of relative (percentage) density for this
analysis masks out the considerable density variance
encountered, and seems more appropriate for defin-
ing faunal or ecological provinces irrespective of
standing-stock distributions within provinces.
Stepwise multiple regression analyses (BMD-02R)
were then employed to define correlations between
major species distributions and environmental factors.
For these results, the increase in R^ was accepted as
equivalent to a correlation percentage coefficient for
the factor assessed.
Finally, a series of analysis-of-variance programs
was run (Geist-Ullrich-Pitz, ANOVAR) in order to
assess seasonal and annual fluctuations in density
and standing stock of the major (indicator) species.
RESULTS
Comparison of sieve fraction results
In order to estimate the effect of using only the
coarse (3-mm) sieve fractions for density, standing-
stock, and species-distribution analyses, one represen-
tative fine (1-mm) sieve fraction was processed from
each of 108 of the 176 quantitative stations and the
results were compared to coarse-fraction results from
the same station and sample (Table 62-1).
Averaged over the total samples analyzed, compari-
son of fine to coarse sieve fraction results indicates
that only about half of the species present are re-
tained by the coarse sieve, and only about one-third
of the population in terms of individual organisms per
unit area are sampled, although roughly 90 percent of
the biomass is retained, averaged over the total
sample area. Since this study was concerned pri-
marily with distributions of the biomass resource,
most of the subsequent analyses were directed at the
coarse fractions, which contain the bulk of this
biomass. This is not to imply, of course, that the fine
fractions are biologically unimportant.
Quantitative biological results
From the combined results of coarse and fine sieve
fractions, a total of 472 species were identified from
the stations sampled, encompassing 292 genera and
Benthic invertebrate macrofauna 1073
TABLE 62-1
Comparison of fine to coarse sieve sample results (means)
from benthic stations on the Bering/Chukchi shelf,
with 95-percent confidence intervals
Coarse
Fine
3-mm
fraction
1-mm
fraction
No. species
Density (indiv/m^)
Organic carbon (g/m^ )
Diversity index
13 ± 1
1134 ± 313
10.74 ±216
0.834 ± 0.045
23 ±1
3471 ±792
0.82 ±0.15
0.920 ±0.040
Coarse to fine fraction species in common per station = 5.7
±0.7
Coarse to fine fraction species different per station = 24.2
±1.6
Total coarse and fine fraction species per station = 29.9
±1.9
Percent species in common per station = 19 ± 2%
16 phyla. The most ubiquitous major taxonomic
group in terms of frequency of occurrence, and com-
prising the most species, was the polychaetous anne-
lids, which occurred at 168 of the 176 quantitative
stations and included 143 identified species and 93
genera. Bivalve mollusks were close behind in fre-
quency, occurring at 167 stations but comprising
only 54 species and 29 genera. Gastropod mollusks
occurred at 146 stations, with 76 species and 38
genera. Seventy -six amphipod species and 42 genera
were identified, occurring at 158 stations. Other
taxonomic divisions followed with fewer species
and genera and lower frequency of occurrence.
Contributions to standing-stock values by these major
taxonomic groups are listed in Table 62-2. These
standing-stock values relate only to the coarse sieve
fraction results.
The species index of diversity (Brillouin) of the
176 quantitative stations, based on coarse sieve
fraction results, ranges from a low of 0.093 to a
high of 1.414. The least diverse station lies off the
east end of St. Lawrence Island, while the most
diverse station is offshore in the northern extremes of
the Chukchi.
It should be kept in mind that these standing-stock
and diversity values, averaged as they are over all
stations and over the total sample area, are of limited
reliability and application. For example, most of
the stations are concentrated in the north Bering Sea
region , which thus necessarily biases such mean values
toward that area. Furthermore, although the most
exhaustive possible station coverage was obtained
given the resources available, even within areas where
the station frequency is greatest the patchiness of the
fauna and large local variances in the standing stock
make such mean values marginally acceptable, albeit
of some value for comparison with other regions of
the world.
Nutrient analysis
Dry/wet weight ratios, organic carbon, organic
nitrogen, and caloric analyses were obtained for 68
of the more common taxa encountered. These results
are listed by major taxonomic group in Table 62-3.
Comparison of results from formalin-preserved
versus frozen samples indicated that differences
between formalin and frozen samples were generally
less than within-sample variances in formalin samples
for replicates of the same species. Consequently,
formalin -preserved values were applied for quantita-
tive analyses.
Dominant species
The ranking program indicated that 113 identified
species and 25 taxa not identifiable to the species
level made up 95 percent of both density and carbon
biomass of the coarse fractions. Thirty-five species
and two unidentified taxa accounted for 75 percent,
and only 10 identified species and one unidentified
taxon accounted for 50 percent of both density and
biomass.
For the fine fractions, 50 species and 23 unidenti-
fied taxa comprise 95 percent, 17 species and 6
unidentified taxa comprise 75 percent, and 6 identi-
fied species account for 50 percent of both density
and biomass.
From the 113 species comprising the 95 percent
of the coarse-fraction density and biomass, 89 species
(Table 62-4) were selected as indicator species for
correlation with environmental factors and for
clustering station and species affinity groups. From
the 50 species comprising 95 percent of the fine-
fraction density and biomass, 44 species (Table 62-5)
were selected for the same purposes.
Station cluster analysis
On the basis of presence or absence and compari-
son of relative density of the 89 coarse-fraction
indicator species, a cluster analysis was performed on
the 176 quantitative stations. According to this
analysis, eight major station groups, or faunal assem-
blages, could be distinguished. As may be seen in
Fig. 62-2, several of these groups are not contiguous
but are separated into areal subgroups, sometimes
with major noncontiguous elements in both the
Bering and Chukchi seas. The biological and physical
characteristics of these station groups, and the species
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TABLE 62-4
Dominant (95-percent cumulative density, wet weight, or
organic carbon standing stock) species encountered within
the 3-mm sieve fraction at benthic stations on the
Bering/Chukchi shelf
Mollusca
Bivalvia
Astarte borealis
A. montegui
Clinocardium ciliatum
Cyclocardia crebricostata
Liocyma fluctuosa
Macoma brota
M. calcarea
M. lama
M. loveni
Musculus niger
Nucula tenuis
Nuculana minuta
N. radiata
Pseudopythina rugifera
Serripes groenlandicus
Tellina lutea
Thyasira flexuosa
Yoldia hyperborea
Y. scissurata
Gastropoda
Cylichna nucleola
Tachyrhynchus erosus
Annelida
Polychaeta
Ampharete acutifrons
A. reducta
Anaitides groenlandica
Antinoella sarsi
Arcteobia anticostiensis
Artacama proboscidea
Axiothella catenata
Brada ochotensis
B. villosa
Capitella capitata
Chaetozone setosa
Chone duneri
C. infundibuliformis
Cistenides granulata
C. hyperborea
Flabelligera affinis
Glycinde wireni
Haploscoloplos elongatus
Harmothoe imbricata
Lumbrinereis fragilis
Maldane sarsi
Myriochele heeri
Nephthys caeca
N. cilia ta
N. longasetosa
N. rickettsi
Nicolea venustula
Nicomache lumbricalis
Phloe minuta
Polynoe canadensis
Potamilla neglecta
Praxillella praetermissa
Proclea emmi
Scalibregma inf latum
Spiophanes bombyx
Sternaspis scutata
Terebellides stroemi
Travisia forbesii
Arthropoda
Amphipoda
Ampelisca birulai
Ampelisca macrocephala
Anonyx nugax pacifica
Byblis gaimardi
Ericthonius tolli
Haploops laevis
Lembos arcticus
Melita dentata
M. formosa
M. quadrispinosa
Paraphoxus milleri
Pontoporeia femorata
Protomedeia fascata
P. grandimana
Cumacea
Eudorella emarginata
Echinodermata
Echinoidea
Echinarachnius parma
Strongylocentrotus droebachiensis
Holothuroidea
Cucumaria calcigera
Ophiuroidea
Diamphiodia craterodmeta
Gorgonocephalus caryi
Ophiura flagellata
O. maculata
O. sarsi
Sipunculida
Golfingia margaritacea
Priapulida
Priapulus caudatus
Echiurida
Echiurus echiurus
Chordata
Ascidiacea
Chelyosoma inaequale
Molgula siphonalis
Pelonaia corrugata
Styela rustica
exhibiting dominance within them, are presented
in Tables 62-6, 62-7, and 62-8.
Less certain results were produced when a cluster
analysis was performed using the results from the 108
fine-fraction samples analyzed. For this cluster
analysis, the 44 species selected from the fine-sieve
fraction ranking program were used as indicator
species. It appears from the cluster dendogram that
all the fine-fraction stations fall into two major
groups, each of which has a minimum affinity be-
tween stations of no better than 0.22. This affinity
level is at least as good as that indicated for some of
the coarse-fraction cluster groups; however, the
stations do not fall into discrete patterns like those of
the coarse-fraction clusters, but appear to be dis-
tributed more or less at random over the study area.
These two large cluster groups could be broken down
into smaller station groups with some degree of
Benlhic invertebrate macrofauna 1077
TABLE 62-5
Dominant (95-percent cumulative density, wet weight, or
organic carbon standing stoci<) species encountered
withiin the 1-mm sieve fraction at benthic stations
on the Bering/Chukchi shelf
Mollusca
Bivalvia
Macoma calcarea
Nucula tenuis
Nuculana minuta
Pseudopythina rugifera
Thyasira flexuosa
Yoldia hyperborea
Annelida
Polychaeta
Anaitides mucosa
Brada villosa
Capitella capitata
Chaetozone setosa
Eteone longa
Glycinde armigera
Haploscoloplos elongatus
Lumbrinereis fragilis
Myriochele heeri
Phloe minuta
Praxillella praetermissa
Prionospio malmgreni
Scalibregma inflatum
Sternaspis scutata
Terebellides stroemii
Travisia forbesii
Arthropoda
Amphipoda
Aceroides latipes
Ampelisca birulai
Ampelisca macrocephala
Anonyx nugax pacifica
Bathymedon nanseni
Byblis gaimardi
Corophium crassicome
Harpinia gurjanovae
Haus tortus eous
Orchomene lepidula
Paraphoxus milleri
P. simplex
Photis spasskii
Pontoporeia femorata
Protomedeia fasciata
P. grandimana
Cumacea
Eudorella pacifica
Eudorellopsis deformis
Leucon nasica
Leucon #2
Echinodermata
Ophiuroidea
Diamphiodia craterodmeta
Priapulida
Priapulus caudatus
areal integrity, but such an effort would result in a
large number of small cluster groups of low affinity
and doubtful reliability. Consequently, analysis of
the fine-fraction results was suspended and effort
concentrated on the coarse-sieve fractions.
Species cluster analysis
For the 89 indicator species selected for the coarse-
sieve fraction station cluster analysis, species-species
cluster analysis was also performed for the entire area
with inconclusive results. Although a total of eight
major species clusters, corresponding vaguely to the
eight major station clusters, did appear to be discern-
ible, the minimum affinity level within these major
groups was so low (less than 0.10) that confidence in
their reliability is limited.
Cluster analysis was next performed on the 89
indicator species within station cluster groups; a
separate species-species cluster was produced for each
of the eight major station groups. The results were
somewhat more satisfactory than those produced
when clustering species over the study area as a
whole, although more questions seemed to be raised
than answered by these results. At the 0.50 or
higher affinity level, 83 species clusters or affinity
groups were generated over all eight station groups,
ranging from 2 to 7 species per species cluster group
and from 5 to 15 species cluster groups per station
group. Although not particularly enlightening in
themselves, these species cluster analyses did invite
questions concerning interspecific distributional rela-
tionships, to be discussed in a later section.
Environmental correlations
The next procedure after the station and species
cluster analysis was to attempt stepwise multiple
regression analysis (BMD02R) relating major species
density distribution (indiv/m^ ) to latitude, longitude,
depth, and sediment mode particle-size.
Temperature, salinity, and oxygen values were not
used for faunal correlation analysis. It is believed
that winter temperatures do not greatly affect the
distribution of faunal complexes in this region
(Neiman 1960), although summer temperatures
probably do (Neiman 1963). Unfortunately, far too
few summer temperatures were available, at specific
stations, to permit a valid correlation analysis. Salini-
ty values are generally fairly uniform over the study
area and probably, with the possible exception of
some nearshore regions near large freshwater sources
such as the Yukon River, do not exhibit extremes
likely to influence faunal distributions. Oxygen
values are likewise fairly uniform, are always near
saturation, and are nowhere considered biologically
limiting.
B E R I N
t::;:i
GROUP 1
m
GROUP II
m
GROUP III
m
GROUP IV
m
GROUP V
m
GROUP VI
YA
GROUP VII
D
GROUP VIII
Dutch hARBOR
^^L
»*-
Figure 62-2. Station cluster groups as determined by benthic faunal similarities on the Bering/Chukchi shelf.
1018
Benthic invertebrate macro fauna 1079
This correlation analysis yielded rather grati-
fying, although not particularly startling, results.
Of the 89 species assessed, 50 percent or more of the
density distributional variability of 26 species could
be accounted for by the four environmental factors
used. Of these 26 species correlated at the greater
than 0.50 (increase in R^ ) level, 21 indicated a
dominant distributional relationship with sediment
particle-size. Two of the remaining five correlate
most strongly with longitude, three with latitude.
Seasonal and annual fluctuations
The final statistical procedure applied to the
quantitative distributional data was a series of 20
separate analysis-of-variance programs intended to
assess seasonal and annual variation in density and
standing-stock (carbon) biomass.
The first such analysis assessed possible variations
in total standing-stock carbon biomass between sum-
mer and winter over the five years during which
sampling took place. With 3/1 degrees of freedom,
this analysis yielded an F-ratio of 12.846, indicating
no significant variation between summer and winter
in total standing stock over the study area.
The second analysis assessed annual variation in
total carbon standing stock over the entire area in
which winter sampling took place, using station data
from the years 1970, 1971, and 1972. With 2/41
degrees of freedom and a 3 X 1 split plot factorial
design with N=181, this analysis resulted in an F-
ratio of 0.617, insufficient to indicate any significant
variation. A similar analysis of annual variation in
summer standing stock over the study area for the
years 1973 and 1974, using a 2 X 5 design vdth
N=20, also indicated no significant variation.
Failing to discern any significant seasonal or annual
variation in standing-stock carbon biomass within
the entire study area, analysis of variance was per-
formed on density and standing stock of selected
major species within selected station cluster groups.
The only statistically significant variations appeared
to be annual density fluctuations for the echinoid
Echinarachnius parma with cluster Group II and the
amphipod Pontoporeia femorata within cluster Group
VIII, between the summers of 1973 and 1974 and be-
tween the winters of 1970, 1971, and 1973 respec-
tively .
Either within the study region as a whole or
within selected species and cluster groups, there
appears to be little discernible fluctuation, seasonally
or annually, in density or standing stock. This
apparent stability may be real or an artifact reflecting
sampling technique, since resources and logistics
could not support a sampling program, either spatial
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1080 Benthic biology
or temporal, designed around this null hypothesis.
Population distributions also tend to be extremely
patchy (Rowland 1973, Stoker 1973), particularly in
the central Bering Sea, further compromising this
analysis. In any event, this problem of annual and
seasonal fluctuation (or lack of it) deserves further
attention.
DISCUSSION
Standing stock
The 300 ± 51 g/m^ benthic standing stock (wet
weight) averaged over the eastern continental shelf
of the Bering and Chukchi seas from the results of
this study seems to conform fairly well to quantita-
tive assessments of other high-latitude North Ameri-
can and Asian benthic faunas. The estimates of 20-
400 g/m^ wet weight for the East Greenland region
(Thorson 1934), 160-387 g/m^ wet weight for
Northwest Greenland (Vibe 1939), 200-300 g/m^
wet weight for the Baffin Island region (Ellis 1960)
and 200 g/m* wet weight for the Sea of Okhotsk
(Zenkevitch 1963) all fall within this range. Even the
very high standing-stock estimates of 1,481 g/m^
wet weight and 3,500 g/m^ wet weight for bivalve
(Serripes groenlandicus) communities of the north-
western and eastern Greenland regions, respectively
(Vibe 1939), are not much higher than the 1,000 to
more than 2,000 g/m^ values observed at several
stations in the northern Bering Sea and Bering Strait
region. The estimates of 20 g/m^ wet weight for the
White Sea and 33 g/m^ for the Baltic (Zenkevitch
1963) indicate that these regions are, on the other
hand, quantitatively depauperate as compared to the
Bering/Chukchi shelf.
The mean values of 300 ± 51 g/m^ , somewhat
higher than previous estimates for the eastern Bering
shelf (Neiman 1960, Stoker 1973), remain within the
bounds of those estimates. The higher mean value
obtained by this study reflects the high benthic
standing-stock values observed in the Bering Strait
region, which was not included in the sampling
schemes of previous studies.
The most apparent, or most readily recognizable,
correlation of standing-stock distribution over the
study area is with latitude. Averaged and plotted out
against degrees of latitude, the station means (organic
carbon g/m^ ) would, if smoothed, come close to
describing a normal bellshaped curve (Fig. 62-3)
with the mode in Bering Strait at 65-68°N latitude.
However, the standard deviations and 95-percent
confidence limits associated with these mean values
are often quite large, mostly as a result of the smaU
number of stations available, particularly north of
Bering Strait.
From the available information and observations,
it seems probable that this rapid rise in benthic
standing stock in the Bering Strait region and the
maintenance of such relatively high levels of standing
stock considerably north of the strait is the result of
several conditions. One of these is the high primary
productivity rate observed in the Bering Strait region
in early to late spring (McRoy et al. 1972). Direct
correlations between benthic biomass and the pri-
mary productivity of the overlying water have not
been firmly established for this region , but they have
been for other areas (Rowe 1969, Mclntyre 1961)
and are assumed to apply here as well.
A second major factor which seems likely to be
influential in this standing-stock distribution is the
influx of terrestrial detritus from the Yukon and
Kuskokvdm rivers. While the actual contribution of
these rivers in particulate detritus usable by benthic
TABLE 62-7
Observed physical characteristics of benthic station cluster groups on the Bering/Chukchi shelf
Group
Group I
Group II
Group III
Group IV
Group V
Group VI
Group VII
Group VIII
Mean
43
32
48
49
27
63
43
56
Depth (m)
SD
9
10
17
16
12
26
16
17
Sediment mode (phi size)
95%
Conf.
limits (±)
3
4
12
10
6
17
13
5
Mean SD
3.00 0.23
2.72 0.73
0.25 2.75
3.11 1.44
3.47 0.92
5.15 1.51
3.63 0.44
4.10 1.23
95%
Conf.
limits (±)
0.11
0.26
4.38
0.97
0.49
0.96
0.37
0.36
Benthic invertebrate macrofauna 1081
TABLE 62-8
Dominant species occuring within station cluster groups
on tlie Bering/Ciiukchi shelf, with designation
of trophic type^, zoogeographic origin'',
and reproduction type*^
Zoogeo-
Repro-
Trophic
graphic
ductive
Dominant species
type
origin
type
CLUSTER GROUP I
Ampelisca macrocephala
SDF
LAB
B
Byblis gaimardi
SDF
LAB
B
Ampelisca birulai
SDF
PAB
B
Macoma calcarea
SDF
PA
P
Astarte borealis
FF
PA
DD
CLUSTER GROUP II
Tellina lutea
SDF
PA
P
Echinarachnius parma
SDF
PAB
P
CLUSTER GROUP III
Ophiura maculata
SDF
PAB
P
Strongylocentrotus
droebachiensis
SDF
ABP
P
Cistenides granulate
SDF
LAB
P
CLUSTER GROUP IV
Haploscoloplos elongatus
SDF
BOP
P
Protomedeia fasciata
SDF
LAB
B
Yoldia hyperborea
SDF
LAB
DD
CLUSTER GROUP V
Serripes groenlandicus
FF
PA
P
Myriochele heeri
SDF
BP
P
Sternaspis scutata
SSF
BP
P
Diamphiodia craterodmeta
SDF
LAB
P
Gorgonocephalus caryi
SDF
ABP
P
CLUSTER GROUP VI
Maldane sarsi
SSF
BP
P
Ophiura sarsi
CS
PAB
P
Golfingia margariticea
SDF
BP
P
Astarte borealis
FF
PA
DD
CLUSTER GROUP VII
Macoma calcarea
SDF
PA
P
Chone duneri
FF
LAB
P
CLUSTER GROUP VIII
Macoma calcarea
SDF
PA
P
Nucula tenuis
SDF
PAB
DD
Yoldia hyperborea
SDF
LAB
DD
Pontoporeia femorata
SDF
PAB
B
^Trophic Type:
''Zoogeographic Origin:
-Reproductive Type:
FF = Filter Feeder
SDF = Selective Detritus Feeder
SSF = Substrate Feeder
OC = Carnivore/Scavenger
ABA = Arctic/Boreal Atlantic
ABP = Arctic/Boreal Pacific
LAB = Low Arctic/Boreal
PAB = Pan Arctic/Boreal
PA = Pan Arctic
BOP = Boreal Pacific
BP = Bipolar
P = Pelagic Larvae
B = Brooding Behavior
DD = Direct Development
organisms is open to question (McRoy and Goering
1976), it is assumed to be substantial.
A third factor, or mechanism, which probably
affects this benthic standing-stock distribution is
the current structure of the Bering and Chukchi seas.
Near-surface currents, which probably extend to the
bottom over much of the shelf, move north along the
eastern side of the shelf (Takenouti aind Ohtani
1974), often at a considerable rate. They are bottle-
necked at Bering Strait, where the velocity of this
northward flow is increased greatly, and subsequently
fan out over the Chukchi shelf at reduced velocities
(Creager and McManus 1966). Much of the near-
surface primary productivity of the northern Bering
may be swept north and transported through Bering
Strait into the southern Chukchi, where reduced
current velocities permit it to settle to the bottom.
Likewise, the influx of detritus from the Yukon and
Kuskokwim rivers may be entrained in this northward
flow and held to the eastern side of the Bering by the
Coriolis effect (Fleming and Heggarty 1966). Near its
source, this riverine detritus, consisting in large part
of coarser and heavier inorganics which leave a
smothering wake, may be a deterrent to benthic
fauna. The more readily suspended particulates,
however, including fine organic detritus, may be
maintained in the current stream until the constric-
tion of Bering Strait is passed and the decreasing
velocity allows settling. Some of this detritus may
settle out along the way, notably in the central
Chirikov Basin between St. Lawrence Island and
Bering Strait.
A fourth consideration, possibly a major one,
which should be taken into account concerning the
quantitative distribution of benthos over the Bering/
Chukchi shelf is the distribution of predators.
Benthic-feeding fish populations seem to be largely
excluded from the region north of St. Lawrrence
Island by low bottom temperatures; their absence
may help to account for the large standing stock of
benthic invertebrates observed in this area as opposed
to the relatively low standing stock in northern
Bristol Bay, heavily used by benthic-feeding fishes in
the summer months (Neiman 1960).
Likewise, predation pressure from the Pacific
walrus population, some 150,000 animals, is con-
centrated on the southern and central Bering shelf.
A large complement of this walrus population, some
tens of thousands of animals, resides the year round
and exerts year-round predation pressure in the
northern Bristol Bay region. During the ice-bound
winter months the bulk of the population resides
along the ice edge on the southern shelf and in the
area between St. Lawrence and St. Matthew islands,
1082 Benthic biology
where ice conditions are favorable (F. H. Fay, Uni-
versity of Alaska, personal communication). Most
of this walrus population does migrate back and
forth across the northern Bering and southern and
central Chukchi, although residence times on this
part of the shelf are much shorter than on the more
southern wintering grounds. During the summer
months, when the Bering and Chukchi are largely
ice-free, this population maintains itself along the
edge of the permanent pack ice in the northern
Chukchi Sea.
In addition to natural predation, commercial
fisheries utilizing the continental shelf, particularly
the Bering Sea south of St. Lawrence Island, are
undoubtedly affecting the benthos of the region to
some degree both through species removal and sub-
strate disturbance. A subtidal clam-dredge fishery
proposed for the southern Bering Sea/Bristol Bay
region could result in greatly increased benthic
disturbance and species removal in the future and
might come into direct competition with the marine
mammals, particularly walruses, which winter in
that area (Stoker 1977).
The curve generated by plotting station diversity
against latitude seems to support the idea that the
standing-stock biomass of the Bristol Bay /southern
shelf region may be depressed by predation. As Fig.
62-4 shows, diversity is highest in the southern Bering
Sea, where standing stock is depressed, and in the
northern Chukchi Sea. This may indicate that,
although the productivity may be high (in the south-
em Bering Sea at least), the standing stock is reduced
by predation (Pianka 1966, Sanders 1968). Diversity
seems to decline in the Chirikov Basin region, where
most of the large standing stock is composed of a
few dominant amphipod and bivalve moUusk detrito-
phages, then rises again in the southern and central
Chukchi to about the same level as in the southern
35 r—
-E 25 —
z
o
00
<
U
U
z
<
cc
o
^
o
o
h-
M
o
z
5
z
<
Figure 62-3. Relationship of standing stock biomass (org. C g/m^ ) to latitude (°N) on the Bering/Chukchi shelf.
Benthic invertebrate macro fauna 1083
I
Bering. This northward increase in diversity beyond
Bering Strait, somewhat at odds with most theories
of high-latitude fauna, may reflect the large influx of
food into this area. Apparently this influx is reliable
and constant enough to permit competition and
diversification of feeding techniques, resulting in
increased species diversity in a region where the
physical stress of the environment would normally
have the opposite effect. This increased diversity
in the northern Chukchi may also reflect predation
pressure by marine mammals (walruses and bearded
seals), which summer along the edge of the arctic
pack ice.
In summary, benthic standing stocks on the
Bering/Chukchi shelf are determined by levels of
primary productivity, current structure and velocity
(both dictating food availability), and benthic-feeding
fish and marine mammal predation, and only coin-
cidentally by depth, sediment type, and latitude.
Salinity, except perhaps near the mouths of the
Yukon and Kuskokwim rivers, is probably never
variable enough to be a major factor, nor is dissolved
oxygen content, which everywhere seems near the
maximum. Winter temperatures near bottom are
probably not important as a distributional influence,
since they are always near the minimum over the
study area. During the summer, however, these
bottom temperatures may be important as a mech-
anism regulating the distribution of benthic-feeding
fish and may effect the reproductive potential of at
least some benthic bivalves (Hall 1964).
Over most of the study region, the distribution of
benthos appears to be extremely patchy. This is
particularly true of the central Bering shelf from St.
Matthew and Nunivak islands to just north of St.
Lawrence Island. The reasons for this patchiness are
uncertain, but it is thought to be largely the result,
directly or indirectly, of variable substrate conditions.
1.3001—
1.200
1.100
1.000
g 0.900
£ 0.800
>
0.700
0.600
0.500
0.400
57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72
LATITUDE
Figure 624. Relationship of diversity (Brillouin) to latitude (°N) on tiie Bering/Chukchi shelf.
1 084 Benth ic b iology
Predation, particularly by walruses, may also be
influential, since the central Bering shelf, where such
patchiness is most characteristic, is the main winter
range of most of the walrus population.
Other probable causes of patchiness are intra-
specific in nature. The reliance of many high-latitude
species on direct development of larvae rather than
on pelagic dispersal (Thorson 1950) would seem to
discourage uniformity in distribution. Many of the
non-dominant species, for this reason or others, do
appear to be clumped rather than uniformly distrib-
uted, as has been observed elsewhere (Hairston 1959).
In the large filter -feeding bivalve mollusks (which do
produce pelagic larvae), this notable clumping ten-
dency results not only in patchiness but also in
distinct age- and size-class segregation. In no in-
stance, in fact, were more than one age-class of
Clinocardium observed at the same sample location.
This tendency to age and size segregation is also
apparent in other filter-feeding bivalves such as
Cyclocardia crebricostata, Hiatella arctica, and
Serripes groenlandicus, although not so pronounced
as in Clinocardium. This phenomenon, also observed
by Vibe (1939) in Greenland mollusk populations, is
probably either the result of cannibalism, the adult
filter-feeders indiscriminately consuming their own
settling spat, or of substrate conditioning by the
adults to preclude spat settlement.
Feeding type
The trophic (feeder) types encountered over the
study area seem to support the view of a detritus-
based benthic food web. The majority of dominant
species in any given area are detritus feeders, either
selective detrito phages or substrate feeders, with a
complement of filter feeders (mostly bivalve mol-
lusks). The distinction between selective detritus
feeders, which may also act as facultative filter
feeders, and primary filter feeders which are in fact
probably filtering and feeding on detritus, is vague
and may be meaningless here. Furthermore, the
virtual exclusion from the benthic samples of the
large bivalves of the genera Mya and Spisula, both
filter feeders, may have compromised present as well
as past views of the trophic structure of the Bering/
Chukchi shelf.
Most of the faunal assemblages possess elements
of all four trophic (feeder) types recognized in this
study (filter feeders, selective detritus feeders, sub-
strate feeders, and carnivore/scavengers). In general,
the distribution and relative dominance of these
trophic types is determined by, or is correctable
with, substrate conditions, as has been observed by
previous investigators (Rhoads and Young 1970,
Neiman 1960). Filter feeders seem more inclined,
for obvious reasons, toward areas of coarse substrate,
relatively low sedimentation rates, and increased
current intensity such as prevail in the northern
Bering Sea/Bering Strait region. Selective detritus
feeders seem to prefer areas of sand or sandy mud at
intermediate depths; substrate feeders are typically
found in deeper water on finer sediments rich in
organics. The distributions of carnivore /scavengers
are, of course, independent of such considerations.
Of the 89 indicator species (Table 62-4), 49 are
considered selective detritus feeders, 9 are substrate
feeders, 16 are filter feeders, and 14 are carnivore/
scavengers (Kuznetsov 1964). Of these same 89
species, 28 are thought to exhibit either brooding
behavior or rapid, direct development of eggs and
larvae, whereas 55 rely on pelagic larval forms
(Stanley 1970; G. M. Mueller, Univ. of Alaska,
personal communication). Furthermore, of these 89
species, 27 are considered Pan-Low Arctic Boreal in
origin, 21 Arctic Boreal Pacific, 17 Pan-High Arctic
Boreal, 9 Pan -Arctic, 10 Bipolar, 4 Boreal Pacific, and
only one Arctic-Atlantic (Ushakov 1955, Guryanova
1951), giving the fauna of the region a strongly
Boreal-Pacific character, as previously postulated
(Sparks and Pereyra 1966). It is also possible, though
not proved, that the cold summer bottom tempera-
tures in the Chukchi Sea, and perhaps over some of
the northern Bering Sea, may necessitate recruitment
into these areas, for at least some of those species
producing pelagic larvae, from warmer waters to the
south (Sparks and Pereyra 1966). If this is found to
be true, then the Chukchi Sea depends upon the
Bering not only as a major source of food but also as
a spawning ground .
Cluster group
As mentioned earlier, cluster analysis resulted in
eight major station groups, several of which are com-
posed of at least two subgroups with discrete areal
distribution. Although these cluster groups may be
considered faunal communities or assemblages,
caution should be exercised in doing so, since the
species themselves do not appear to exhibit strong
affinities with one another.
These cluster groups appear, in a very general
sense, to form broad bands parallel to the mainland
coast (Fig. 62-2). This is particularly true of Groups
II, IV, V, and VI. Group I, exhibiting the greatest
cohesiveness of all the groups in affinity levels, is
confined to the Chirikov Basin and the nearshore
region adjacent to St. Lawrence Island. It is perhaps
significant that the sediment structure of this area is
also the most uniform encountered in particle-size.
Benthic invertebrate macro fauna 1085
indicating a strong relationship between sediment and
fauna. Group VII, divided in distribution between an
enclave north of St. Lawrence Island and another
north of the Pribilof Islands, appears likewise to be
governed by sediment type. While the depths of these
two enclaves are significantly different (means of 35
and 69 m), the mean sediment particle-sizes are
quite similar (3.80 and 3.00 phi). Group III, another
group with split distribution, occurs only within
Anadyr Strait and Bering Strait and is probably
controlled by current structure and bottom type.
Group VIII, the Central Bering Supergroup, has
distributions in both the Bering and Chukchi seas and
possesses considerable faunal and environmental
complexity. In general, the major correlative element
of all these cluster groups seems to be sediment type,
although often this factor may in itself reflect other
variables such as current regime. Several of these
cluster groups correspond closely to the distribution
of Bering Sea water masses (Fig. 62-5) as defined by
Takenouti and Ohtani (1974).
Almost always when a cluster group has split areal
distributions, the standing-stock biomass of the more
northern distribution appears to be higher than that
of the southern, supporting the hypothesis of south
to north increase in standing stock over the study
area. Unfortunately, the variability of standing stock
within groups is such that this trend can be supported
at the 95-percent confidence level only for Cluster
Group VI.
This observed tendency for station groups and
faunal assemblages to be repeated in the Bering and
Figure 62-5. General patterns of surface circulation and extent of water masses over the Bering Sea continental shelf From
Takenouti and Ohtani (1974).
1086 Benthic biology
Chukchi seas illustrates clearly the similarities and
interdependence of the two regions. The original
organization plan for this study was to consider the
two regions, the continental shelves of the Bering Sea
and the Chukchi Sea, as separate entities. As data and
information became available, however, it became
increasingly apparent that such a distinction was
artificial, and that this entire continental shelf should
be considered one integral biological system.
Environmental correlations
The results of correlating species distributions with
environmental variables also strongly support the
view that sediment is in fact the variable most direct-
ly correlatable with the distribution of species over
this continental shelf.
This relationship between species and the environ-
ment is, within the context of this discussion, just
what it purports to be— a distributional correlation,
nothing more or less. It may be useful for prediction,
but it does not necessarily define a direct cause-and-
effect relationship. Sometimes organisms may seek
out a distinct substrate type for its ov^ti pecularities—
for attachment, for burrowing or tube-building, or as
a nutrient source for substrate feeders. But more
often it seems probable that these distributions,
faunal and geological, are dictated by some other
agent or agents such as current velocity and direction
(also relatable to depth, latitude and longitude, etc.)
and sedimentation rates and sources.
The second most strongly correlatable environ-
mental factor apparent from this study is latitude,
with longitude not far behind. This is certainly not
a direct cause-and-effect relationship, but reflects
other conditions such as bottom temperature, pri-
mary productivity distributions, distance from
shore, and current regime. The same is probably true
of depth, which does not appear, from either the
species/environment correlations or the cluster group
distributions, to be particularly influential in itself.
It is highly probable that the other environmental
variable which would, were sufficient data available,
prove strongly correlatable with faunal (species)
distributions is summer bottom temperature (Neiman
1960, Filatova and Barsanova 1964). The tempera-
ture effect is probably direct, affecting the repro-
ductive capacity of the species. For forms with
pelagic larvae, the temperature effect may not be so
critical, since recruitment is possible from other areas,
as is true of the fauna of the Chukchi and northern
Bering. For forms exhibiting direct development or
brooding behavior, however, this factor may be
critical in determining distributions. This is postu-
lated to be true of the ophiuroid Ophiura sarsi
(Neiman 1960). As more data become available, the
present prediction is that these two factors, sediment
type and summer bottom temperature, will be found
to be overridingly dominant in correlations, for
predictive purposes, with faunal distributions.
Regarding interspecific faunal associations, caution
should be exercised in ascribing "community"
characteristics to species assemblages within station
clusters. In cluster analyses on indicator species,
either within station cluster groups or over the area as
a whole, no strong and repeated interspecific affini-
ties were perceived, although local interspecific
affinities were sometimes quite strong. It is not
entirely clear what this indicates, but it is possible to
infer that biological interactions between species,
with the exception of possible predator-prey relation-
ships, are not particularly strong and that within-
group distributional preferences are probably dictated
by variations in the physical environment. Species
distributions are probably controlled not by one but
by several such environmental variables, which
perhaps accounts for the lack of constancy in species
associations within the various groups or areas.
This view seems further supported by the curious
repeated occurrence within the same group, and
often within the same station, of related species of
the same genus. The evidence of the cluster analysis,
however, is that such related species seldom indicate
any distributional affinity for one another. The
inference is that, although concurrent, these closely
related species are in fact seeking out slightly variant
microhabitats where slightly different lifestyles
enable them to coexist without recourse to exclusive
competition. Indirect support of this argument can
also be drav^ni from previous observations of the
extreme patchiness of the benthic fauna of the
central and northern Bering shelf, which would seem
to indicate such variable microhabitat.
Season and annual stability
A total of 20 separate analyses of variance were
performed in order to evaluate possible seasonal
and annual fluctuations. For only two species,
Echinarachnius parma and Pontoporeia femorata,
were any significant statistical fluctuations indicated.
These fluctuations were both variations in density
(indiv/m^ ) rather than changes in biomass; both were
valid for only one area (station cluster group) and at
the 95-percent confidence level but not at the 99-
percent level. Admittedly, since the sampling pro-
gram was not designed around the null hypothesis
of such variability, severe statistical constraints were
necessary. Even so, the obvious interpretation of
these analyses is that the Bering/Chukchi benthic
Benthic invertebrate macrofauna 1087
system, for all its distributional complexity and
variability, is remarkably stable in population for
such a high-latitude fauna (Sanders 1968, Holmes
1953). In a sense, however, this is not entirely sur-
prising (MacArthur 1955), given the rather high
species diversity over much of this area, a diversity
which itself seems uncharacteristic for such latitudes.
This high diversity and stability of standing stock
may also indicate a reliable and relatively uniform
benthic food supply.
Another possible reason for this population stabil-
ity may lie in the reproductive nature of the fauna
itself. Many of the species exhibit direct larval
development or brooding behavior and are thus less
prone to annual recruitment failures than those forms
with pelagic larvae (Thorson 1950, Paul and Feder
1973).
CONCLUSION
The benthic fauna of the Bering/Chukchi shelf
appears to be a dynamically stable though distribu-
tionally complex system of considerable diversity— of
habitat and faunal assemblages, of species within
these assemblages, and perhaps of sources of food
supplying these assemblages.
There appear to be eight major faunal assemblages,
each composed of several subgroups, which form a
distributional mosaic within the study area. The
distribution of these groups, at first glance dishearten-
ing in complexity, appears upon inspection to cor-
relate strongly with substrate type. This seems
to be true also of species distributions, although
summer bottom temperatures may also influence
both species and assemblage distributions. The close
correlation between substrate type and faunal
distributions is not to be taken literally as a cause-
and-effect relationship. It is often merely a reflection
of other environmental conditions which dictate
both faunal and sediment distributions. It serves
a predictive, not necessarily a determinant, role.
The benthic fauna of this shelf, in general, appears
to maintain a fairly high level of standing stock,
though not abnormally high relative to comparable
areas in the high-latitude Atlantic and Asian Pacific.
The features of this Bering/Chukchi fauna which do
seem somewhat at variance with such comparable
regions are its relatively high faunal diversity, dy-
namic stability, and latitudinal distribution of stand-
ing stock. Both diversity and standing stock tend to
increase dramatically from south to north.
Clues to this situation are thought to be found in
the physical/biological system which supplies food
to this benthic fauna and in the character of the
fauna itself. The contribution of nutrients to the
benthic ecosystem is thought to come from two
main sources— primary productivity and riverine
detritus. The dependability and diversity of this
nutrient system probably accounts in large part
both for the dynamic stability of the benthic popula-
tion and for its diversity.
The physical system of currents associated with
this nutrient system tends to sweep the bulk of the
food supply across the shelf northward, where it is
funneled through Bering Strait and dumped, because
of decreasing current velocity, into the southern and
central Chukchi Sea. Presumably this accounts for
the remarkable increase in standing stock in this
region.
The faunal system itself is largely dominated by
detritus feeders, with a considerable complement of
filter feeders, and so is geared to take advantage of
this diversity in nutrient sources. Because the fauna
is also composed, to a large extent, of forms exhibit-
ing direct larval development, it is less subject to the
population (recruitment) fluctuations suffered by
forms producing pelagic larvae.
In the southern Bering and the northern Chukchi,
the latitudinal extremes of the system, decreased
standing stock and increased diversity, are encoun-
tered, perhaps for similar reasons. In the southern
Bering Sea, standing stock is probably reduced
through predation, even though productivity and
diversity are maintained at high levels as a result of
decreased environmental (physical) stress and the
availability of food. In the northern Chukchi, de-
creased availability of food and increased environ-
mental stress may account for the low standing stock
(and probably low productivity). The relatively
high diversity observed in the northern extremes
may reflect competition and replacement of Boreal-
Pacific forms, which dominate most of the region, by
arctic and Atlantic forms, or it may indicate increased
pressure of marine mammal predation.
The evidence seems to indicate that faunal assem-
blages of the Bering/Chukchi shelf are governed by
physical, environmental variables and are not strongly
interrelated biologically. In this sense they are not
true biological communities, but rather consist of
flexible confederations of species loosely allied by
similar environmental requirements.
Perhaps the most important conclusion developed
from this study, in terms of possible perturbation
effects, is the seemingly very strong dependence of
the Chukchi system on the Bering Sea as a source
of nutrients and possibly as a spawning ground pro-
viding recruitment. The Chukchi is, in this sense,
a somewhat saprophytic system and is apt to reflect
1088 Benthic biology
strongly, or even magnify, events which affect the
Bering Sea itself.*
Hairson, N. G.
1959 Species abundance and community
organization. Ecology 40:404-16.
Hall, C. A.
1964
Shallow-water marine
moUuscan provinces.
226-34.
climates and
Ecology 45:
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Distribution of benthic fauna in the
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1939 Preliminary investigations on shallow
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A Survey of Benthic Infaunal Communities
of the Southeastern Bering Sea Shelf
y
Karl Haf linger
Institute of Marine Science
University of Alaska
Fairbanks
ABSTRACT
The continental shelf of the Bering Sea south of St.
Matthew Island was surveyed by taking at least five van Veen
grabs at each of 96 stations and sieving organisms with a 1-mm
mesh screen. Multivariate statistical methods were used to
define communities organized in roughly contiguous bands
paralleling local bathymetry. Community boundaries coincide
with frontal zones identified in the area, suggesting a commu-
nity response to water-mass characteristics or differing
between-front depositional environments. Large between-
station variations within the same sedimentary and tempera-
ture regimes were noted, but cannot be interpreted with the
existing data. Standing stocks appeared uniformly low away
from areas with a coastal influx of detritus, with the excep-
tion of an area southeast of the Pribilof Islands that seems
to underlie an intensely productive water column.
INTRODUCTION
This study presents a picture of faunal zonation
on the southeastern Bering Sea shelf based on a set
of samples taken systematically from the Alaska
Peninsula to St. Matthew Island. Implicit in the
approach is the hypothesis that within a geographic
area, similar and relatively stable associations of
species occupy similar habitats. No attempt was
made to challenge the concepts of the uniqueness
or constancy of benthic communities, although a
growing body of literature dealing with many types
of communities (Mills 1967, 1969; Johnson 1970;
Estes and Palmisano 1974; Levin and Paine 1974;
Sutherland 1974; Gray 1977) calls into question
interpretations based on this view. Some of the re-
sults presented here suggest that community variation
in time and space needs to be addressed by investi-
gators of the benthos.
Benthic studies are limited by the inaccessibility
of ocean bottoms. Although the conclusions of those
studying more accessible systems are valuable in
providing concepts and direction to benthic studies.
such problems as the importance of competition,
diversity, and predation, the persistence of systems,
and the limits of stochastic variation cannot be
determined by analogy alone. Experiments involving
manipulation of natural conditions often illuminate
mechanisms that underlie community structure, but
these are not feasible in the present context. It is
hoped that the study discussed here will provide a
basis for working with naturally occurring experi-
mental situations, for these often present otherwise
unavailable insight into the structure and mainte-
nance of communities.
Published studies of benthic invertebrates of
both the eastern and western Bering Sea shelves
remained largely taxonomic in nature until the
works of the Russian investigators Neiman (1960,
1963), Filatova and Barsanova (1964), and Kuznetsov
(1964), began to appear in the early 1960 's. These
cover enormous areas with relatively few samples,
but nonetheless attempt to define causal factors in
community organization. Along similair lines, but
with much more intensive coverage, are the works of
Semenov (1964) and Stoker (1978). The result has
been a much-improved version of community identity
based on faunal types and their correspondence with
sediment and temperature regimes in Bristol Bay
(from Semenov 1964) and the northern Bering Sea/
Chukchi Sea (from Stoker 1978). Fisheries investiga-
tions supplying relevant information on the distribu-
tion of benthic predators are described in the works
of Skalkin (1963), Kihara and Uda (1969), Alton
(1974), Pereyra et al. (1976), and Bakkala and
Smith (1978); in addition, Neiman (1964), in one of
the few nondescriptive studies of the subject,
attempted to relate age distributions of bivalve
moUusks to utilization by predatory fish in two
areas of the southeastern shelf.
1091
1092 Benthic b io logy
STUDY AREA
The area of interest to this study ranges from the
Alaska Peninsula to St. Matthew Island (Fig. 63-1),
thus complementing the existing picture of infaunal
zonation on the shelf, exclusive of Norton Sound.
Since the physical characteristics of this area are
treated at length in other sections of the book, only
salient features distinguishing major shelf zones will
be discussed here. Although the bottom is a very
gradually sloping plane, dramatic differences in both
the sedimentary and water-column environments are
found in cross-shelf transects. Three general zones
have been described:
(1) A coastal domain (shoreline to 50-m water
depth) that is generally homogeneous and subject
to temperature extremes during both summer
and winter. Water movements due to both tidal
and wind mixing apparently limit the sediment
environment to predominantly sand- and gravel-
sized particles (See Figs. 63-2a and b).
(2) A shelf -water domain that is vertically homo-
geneous in winter but strongly stratified in summer,
resulting in low summer bottom temperatures and
a limit to mixing activities with a corresponding
increase in the deposition of silt-sized particles (see
Fig. 63-2b).
(3) An outer-shelf domain of warmer and rela-
tively constant temperature Bering Sea/Alaska
Stream water. The increasing deposition of fine
particles seems to be modified in the shelf-break
area (see Stations 16, 31 in Figs. 63-2a and b).
Although the positions of fronts separating the
water masses appear to vary little annually, bottom
temperature fluctuations do occur on a yearly basis.
Such variance may influence benthic populations in
all domains, but it is probably more significant in
the middle- and outer-shelf areas that do not ex-
perience large annual fluctuations in bottom tempera-
ture. Kihara and Uda (1969) suggest that even minor
changes in what are now termed frontal positions can
lead to marked changes in the success of commercial
fishing operations. Obviously, the significance of
climatic cycles short enough to vary over the lifespan
of many of the community members (1-20 years)
must be considered biologically important.
METHODS
Sample acquisition
The results reported represent two years of samp-
ling at the following times of the year: May -June,
1975 (56 stations from the R/V Discoverer); Sep-
tember, 1975 (6 stations from the Miller Freeman);
180°
175°
170°
165°
160°
155°
175°
170°
165°
160°
Figure 63-1. Southeastern Bering Sea shelf study area and grab station locations.
I
Figure 63-2. Sand and silt particle distribution over the sturdy area: (a) sand fractions (b) silt fractions
(data from Burrell et al., Chapter 19, Volume 1).
1093
1094 Benthic b io logy
and April-June, 1976 (34 stations from the Miller
Freeman). Van Veen grabs, limited to the upper 5
cm in particularly sandy areas, and penetrating to a
maximum depth of 14 cm in finer sediments, were
used with varying degrees of success. Limited pene-
tration of the grab undoubtedly excluded large
deep-living bivalves (especially Spisula and Tellina)
in sandy areas; these have been sampled in nearshore
Bristol Bay by Hughes (Hughes and Bourne, Chapter
67, this volume). One screen size (1 mm) was used
on all replicates (5-10 from each station); hence
the taxa included must be considered macrofaunal
only. All organisms caught on screens were placed
in a buffered, 10-percent formalin solution and
taken to the Marine Sorting Center, Institute of
Marine Science, University of Alaska, for identifica-
tion and weighing.
Data analysis
Ecologists rely heavily on cluster analysis to
describe the composition and extent of biological
communities; its use in the marine environment has
been extensive (see Cassie and Michael 1968, Field
1970, Williams and Stephenson 1973, Grassle and
Smith 1976). Although this method is central to the
development of this study, lack of space prohibits
a discussion of the mechanics of it. Both the Bray-
Curtis and Canberra metric dissimilarity coefficients
were used in the classification of the 1975 data, while
for the incorporation of the 1976 samples the former
was used exclusively. Their formulas, from Clifford
and Stephenson (1975), are given below:
Bray-Curtis: dj^ = . 2 Ixjj— Xik
.2j (Xij+Xik)
Canberra metric: dj^ = ~ 2 I Xjj— Xjk 1/ (Xij+Xj^),
n i= 1
where Xjj represents the value for the ith species at
the jth station. Classification variables generally
take the form of density or proportions, based on
either abundance or weight. The variable chosen
for all work was infaunal density, transformed to the
natural logarithm [x' = In (x + 1)] .
An inverse analysis (the clustering of species)
was also performed (see Williams and Lambert 1961)
using the indices mentioned above. To illustrate the
partitioning of species groups among station groups,
cells are established for each pair of every species
group with each station group, and the density
evaluated as:
n n
Density = 2 S Xii/ns,
i=i j=i "
where n is the number of species in the cell, s the
number of stations in the cell, and Xjj the number of
the ith cell species found at the jth cell station.
Group average and flexible sorting strategies were
employed (Williams and Lance 1977); since they
were in general agreement, only results of the former
will be presented here.
Principal components, principal coordinates, and
multiple discriminant analyses have also been used by
many ecologists for the same functions and have
been relied on for confirmation in the present study.
Detailed discussions of all techniques mentioned may
be found in many standard texts on the subject
(Gower 1966, 1967, 1969; Orloci 1966, 1967;
Blackith and Reyment 1971; Anderberg 1973;
Hartigan 1975; Morrison 1975; Pielou 1977).
Estimates of wet weights and values for standing
stocks or organic carbon derived from these were
used to produce a tentative scheme of distribution
of standing stock over the southeastern shelf. Some
of these figures incorporate contributions from
slow-moving or sessile epifauna not considered in
other parts of this analysis. Moreover, these figures
are biased dowoiward by the omission of deep-living
bivalves; Chapter 67 (Hughes and Bourne, this volume)
illustrates the potential magnitude of this error.
Wet weight to organic carbon conversions for most
phyla, as well as for many classes (Polychaeta, Deca-
poda, Ophiuroidea, Holothuroidea) and many mol-
luscan genera, were taken from Stoker's extensive
work (1978) on the subject.
Information on sedimentary regimes was taken
from OCSEAP studies presented by Burrell et al.
(Chapter 19, Volume 1). Contouring of sediment
and standing-stock data was done using SURFACE II
routines on the University of Alaska Honeywell
6600 computer. The algorithm defines grid point
values from eight nearest neighbors and uses an
inverse-distance weighting function.
RESULTS
Station clustering
Clustering of stations produces the dendrogram
shown in Fig. 63-3. The split between the inshore
and mid-shelf stations indicates an abrupt faunal
transition at the general depth of 50 m, with the
inshore groups (IGl, IG2) including a deeper string
of stations 10, 11, 12, and 13 (1975 only) (see Fig.
63-4a). Small regions in the outer shelf and the head
of Bristol Bay (see Fig. 63-4c) also emerge as faunis-
tically distinct. The Bristol Bay stations are a shallow-
water (30-40 m) group differing from the larger
inshore group in being confined to positions roughly
adjacent to the Alaskan coast, except for station 9,
which lies in slightly deeper water.
Group
Station and
sampling date
.70
.58
.47
.35
.25
.13
SPRING -
76 043 1
SPRING -
75 059 1
SPRING -
75 025-1
75 041-1
76 025 -'
76 041 — '
SPRING -
SPRING -
SPRING -
SPRING -
76 044
p SPRING -
l- SPRING -
75 003
76 003
SPRING -
75 008
IG1A
SPRING -
75 020
SPRING -
75 027
("SPRING -
■-SPRING -
75 040
76 040
SPRING -
75 043 J
SPRING -
75 059 '
SPRING -
75 039
SPRING -
75 001
SPRING -
75 042
SPRING -
75 061
_ SPRING -
75 062
r SPRING -
"- SPRING -
75 012
76 012
IG1B
SPRING -
SPRING -
75 010-1
75 on- 1
76 010-1
76 on — '
SPRING -
SPRING -
r FALL -
L SPRING -
|- FALL -
^ SPRING -
75 047
IG1C
76 047
75 055
76 055
SPRING -
T"" mi
IG2
SPRING -
SPRING -
SPRING -
75 057 1
SPRING -
75 060
MISC.
p SPRING -
1- SPRING -
1- SPRING -
75 004
INSHORE
76 004
75 024
STATIONSLspRiNG -
76 024
75 071
FALL -
FALL -
75 072
SPRING -
75 063
FALL -
75 083
FALL -
75 082
MSGB
FALL -
SPRING -
75 073
76 037—1
SPRING -
75 045
SPRING -
75 939
SPRING -
75 037-1
SPRING -
SPRING -
75 924
SPRING -
75 031
SPRING -
75 036—1
75 015
75 017 1
SPRING -
SPRING -
SPRING -
76 036—'
pSPRING -
1- SPRING -
75 064
76 064
FALL -
75 070
MSGA
pSPRING -
^SPRING -
75 065
76 065
SPRING -
75 018 — 1
SPRING -
76 049 1
SPRING -
76 054
SPRING -
76 069
p SPRING -
l-SPRING -
75 028
76 028
SPRING -
75 018 — 1
SPRING -
75 029
pSPRING -
•-SPRING -
75 019
76 019
75 030
pSPRING -
L-SPRING -
76 030
OSG
SPRING -
76 017 '
SPRING -
75 049 1
_ SPRING -
MISC.
SPRING -
75 014
OFFSHORE SPRING -
75 035
STATIONS
SPRING -
75 015
76 005 — 1
SPRING -
SPRING -
l-SPRING -
l-SPRING -
BRISTOL
75 023
76 023
BAY
nSPRING -
LSPRING -
75 006
76 006
SPRING -
75 005 1
SPRING -
rSPRING -
l-SPRING -
SPRING -
75 007
75 002
MISC
OUTLIERS
76 002
75 038 1
Figure 63-3. Dendogram for all sta-
tions using a Bray-Curtis index and
group average sorting. Similarities
between 1975 and 1976 samples are
indicated by lines at left margin which
link subsequent years of samples from
the same station.
1095
180°
170°
165°
160°
155°
56
53°-
INSHORE STATION GROUPS
H1GIA
P IG1B
H 1G1C
El IG2
I I Misc. inshore stations
J I i L
J 1 \ 1 i L
175
170°
' 165
160°
180°
175°
170°
165
160°
160°
180°
175°
170°
165
160°
155°
OUTER-SHELF AND BRISTOL
STATION GROUPS
Misc. Outer Shelf stations e
170°
165
160°
Figure 63-4. Station groups identified from
dendrograms in Fig. 64-3: (a) inshore groups,
(b) mid-siielf groups, (c) outer-shelf and Bristol
Bay groups.
1096
Infaunal communities 1097
The classification of mid-shelf (MSGA, MSGB)
and outer-shelf (OSG) station groups arises from a
similarly divisive point in the dendrogram (Fig.
63-3). Defined by stations 18, 29, and 36, the mid-
shelf group extends seaward approximately to the
100-m isobath (see Fig. 63-4b). This boundary
should be accepted conditionally for two reasons:
from the Pribilof Islands north no sample data are
available to determine community types in deeper
water, and a set of deeper stations near the shelf
break (31, 16, and 17; 1975 only) is of the mid-
shelf type.
Finally several stations were found to be unallied
to any major station group. The occurrence of a
dense patch of a tunicate (Mogula sp.) at station 2
differentiates it from the rest of the shelf. Station
38 was found to have a typical, if somewhat sparse
(286 ind./m^ £ind 36 species), mid-shelf fauna in
1975; this station was strikingly impoverished (13
species with 64 ind./m^ ) in 1976.
CLUSTERING OF SPECIES
Clustering of 139 species based on their occurrence
throughout the study area results in a dendrogram
analogous to that produced by station clustering
(see Fig. 63-2). This dendrogram is summarized in
Table 63-1, which Lists 85 species that were constitu-
ents of groups of at least three members. Their
densities within the station groups are given in
Table 63-2. These groups are large and therefore a
considerable simplification; they illustrate only very
broad trends in cross-shelf zonation. ;
Group 1 is the most obviously ubiquitous, showing
high densities in all major station groups. Ubiquity
is less characteristic of Group 2 species, which
increase markedly in numbers in the inshore stations.
Groups 3, 4, and 5 also show an inshore /offshore
polarity, evincing an even greater specificity for
inshore stations than Group 2. Groups 3 and 4 are
distinguished from each other by the presence of
Group-3 species in the Bristol Bay station group.
The mid-shelf area is distinct from the inshore
area because of the presence of species Groups 6 and
7, found in fewer numbers in the outer shelf region.
The high density of Group 6 in MSGB is somewhat
misleading; it is inflated by the large numbers (3,030
ind./m^ in 1975 and 2,800 ind./m^ in 1976) of the
bivalve Clinocardium ciliatum found at station 28.
Species from Groups 8-13 are, for the most part,
found in the offshore stations of OSG and individual
stations 14 and 35. They are sporadically present in
the inshore groups, and it is chiefly the differences
in their inshore distributions that distinguish them.
Assessment of standing stock
Contours of wet weight and organic carbon are
shown in Figs. 63-5a and b. Wet-weight values should
be approached with caution; high values found at
stations 2, 4, and 28 may be inflated by high water
content (as in tunicates) or may simply reflect the
presence of shell or exoskeletal material. Two trends
are evident: high values at stations adjacent to the
Alaskan coast and generally low values elsewhere.
An exception is the area centered on station 28 of the
mid-shelf region, where exceptionally dense bivalve
beds were found.
DISCUSSION
Standing stock
High productivity in nearshore communities may
depend on detritus of terrestrial origin. Stations 1
and 2, near Izembek Lagoon, which supports exten-
sive eelgrass (Zostera marina) beds, have very high
standing stocks. Station 24 (again with high standing
stocks) is within range of the Kuskokwim River dis-
charge. Smaller drainages along the coast (Kvichak,
Ugashik, King Salmon, and others) contribute detritus
to benthic communities in Bristol Bay. Neither the
magnitude of this food resource, nor the range in
which it disperses, nor the extent of primary pro-
duction in this area has been studied.
The primairy food source for mid-shelf and off-
shore benthic communities must be derived from
water-column productivity, both in association with
ice and in the open water. Studies of the water-
column system indicate the existence of epontic,
ice-edge, and generalized spring and summer blooms
which, in mid-shelf areas, are largely ungrazed in the
water column as a result of zooplankton community
dynamics (Cooney, Chapter 57, this volume). Al-
though the flux of particulates to the sediment sur-
face has not been measured, it seems certain that a
significant enrichment in the mid-shelf area is respon-
sible for the large standing stocks in that region.
A cautionary note concerning these standing-
stock figures must be interjected. Although it is
tempting to link benthic standing stocks immediately
to both primary and benthic productivity levels,
many unknowns still exist. It seems clear that
the remains of phytoplankton blooms do at times
sink to the sediments, but their role as a food resource
has not been studied. Specifically, microbial and
meiofaunal organisms consume this detritus and, by
virtue of short generation times, are capable of
dissipating sudden energetic inputs to the sediment
surface, and yet their role in this system remains
unassessed.
k
TABLE 63-1
Species groups and their station group preference
Groups with ubiquitous distributions
Group 1
Byblis gaimardi
Capitella capitata
Haploscoloplos elongatus
Harpinia gurjanovae
Magelona pacifica
Nephthys ciliata
Nucula tenuis
Phloe minuta
Praxillella praetermissa
Tharyx sp.
Group 2
Ampelisca macrocephala
Ampharete arctica
Cylichna alba
Eteone longa
Eudorellopsis deformis
Glycinde picta
Hippomedon kurilious
Myriochele heeri
Nephthys caeca
N. longasetosa
Scoloplos armigera
Solariella obscura
Spio filicomis
Travisia forbesii
Inshore groups
Group 3
Anaitides maculata
Diastylis alaskensis
Glycinde armigera
Tachyrhynchus erosus
Westwoodilla caecula
Group 4
Corophium crassicome
Echinarachnius parma
Haustorius eous
Ophelia limacina
Spiophanes bombyx
Spisula poly ny ma
Tellina lutea
Group 5
Ampharete acutifrons
Euchone analis
Yoldia scissurata
Mid-shelf gro ups
Group 6
Axinopsida serricata
Chaetoderma robusta
Clinocardium ciliatum
Diamphiodia craterodmeta
Drilonereis falcata minor
Eudorella emarginata
Heteromastus filiformis
Maldane sarsi
Nephthys punctata
Nuculana pernula
Ophiura sarsi
Scalibregma inf latum
Solariella varicosa
Terebellides stroemii
Thyasira flexuosa
Group 7
Artacama proboscidea
Bathymedon nanseni
Brada villosa
Eudorella pacifica
Eudorellopsis Integra
Macoma moesta alaskana
Polynoe canadensis
Pontoporeia femorata
Priapulus caudatus
Yoldia amygdalea
Y. hyperborea
Miscellaneous small groups
Group 8
Asabellides sibirica
Harmothoe imbricata
Hiatella arctica
Group 9
Ampelisca birulai
Golfingia margaritacea
Peisidice aspera
Group 10
Ampelisca furcigera
Aricidea suecica
Glycera capitata
Group 11
Ampelisca eschrichti
Paraphoxus simplex
Urothoe denticulata
Group 12
Harpinia tarasovi
Lumbrinereis similabris
L. zonata
Group 13
Astarte montagui
Musculus discors
Onuphis iridescens
/
TABLE 63-2
Cell densities for major
station and
species groups
Species group
Station group
(n in group)
IGIA
IGIB
IGIC
IG2
MSGA
MSGB
OSG
BB
1(10)
38.0
29.5
31.0
6.4
61.7
26.8
15.3
0.9
2(13)
30.2
11.1
16.3
6.4
2.1
8.1
5.5
4.1
3(7)
41.6
9.1
7.0
25.3
0.1
2.1
0.1
48.6
4(5)
7.9
0.6
5.8
2.9
0.2
0.9
0.4
0.3
5(3)
6.0
6.4
4.7
1.7
0.2
0.3
5.2
0.0
6(15)
0.7
2.9
24.7
0.5
9.0
26.7
9.3
0.6
7(12)
1.1
1.3
4.9
0.9
21.0
6.0
0.7
0.0
8(3)
0.0
0.4
2.5
0.6
0.1
3.5
16.9
5.8
9(3)
0.0
0.0
0.2
0.0
0.1
0.3
4.9
1.3
10(3)
0.2
0.1
0.0
0.3
2.1
2.2
10.4
5.0
11(3)
0.1
0.1
2.8
0.1
0.0
1.8
4.4
0.7
12(3)
0.0
0.0
0.0
0.5
0.0
10.6
14.0
4.4
13(3)
3.0
1.7
0.0
0.2
0.0
0.1
8.8
1.1
1098
180°
59'
56'
53°
175°
170"
165"
160"
155"
INFAUNAL WET WEIGHT
DISTRIBUTION
(g/m^)
175'
170'
165°
160'
INFAUNAL ORGANIC CARBO
_ DISTRIBUTION
(g/m^)
175°
170"
165"
160
Figure 63-5. Infaunal standing stock over the southeastern shelf area: (a) wet weight, (b) organic
carbon.
1099
1100 Benthicb io logy
Probably of greater significance is our lack of
information on interaction between the infauna and
their epifaunal predators, particularly those fast-
moving predators able to escape capture by grabs
and small trawls. Predation by crabs, asteroids,
bottom-feeding fish, and walruses is well documented
qualitatively, but not well enough to quantify their
effect on gross benthic productivity or to assess the
effect of this pressure on community structure.
Some knowledge of the effect of cropping on age
distributions of bivalve mollusks has resulted from
Neiman (1964) and McDonald et al. (Chapter 66,
this volume), but the space in which this operates
remains undetermined.
Shelf zonation
The major boundaries drawn in this study, between
the inshore (IGl and IG2), mid-shelf (MSG), and
outer-shelf (OSG) regimes, are unambiguous and
indicate strong faunal discontinuities. Somewhat
similar schemes have been proposed by most other
workers in the area (Neiman 1960, Semenov 1964,
Stoker 1978).
Good agreement between station groups and the
boundaries of major water masses in this portion of
the shelf suggests a community response to the
characteristics of water masses. The seaward edges
(50 m and 100 m respectively) of both the inshore
and mid-shelf groups correspond to frontal zones de-
limiting the various water masses of the shelf (see
Coachman and Charnell 1977). Russian investigators
(Neiman 1963, Semenov 1964) have advanced the
hypothesis that variations in both temperature and
sediment type between these areas control benthic
distribution patterns. Residence in nearshore waters
requires some degree of eury thermal tolerance,
since both high summer and low winter temperatures
occur. Mid-shelf waters exhibit a summer thermal
stratification giving rise to cold bottom tempera-
tures that should support a stenothermal, arctic
fauna. Outer-shelf stations (150 m and deeper) are
least subject to either extreme temperature variations
or extreme cold and should correspondingly be
expected to support stenothermal, arctic -boreal
complexes. Reference to the sedimentary regimes
suggests a similar pattern of cross-shelf variations in
large domains. The transition to a silt-deposition
area represents a radically different substrate, and
this substrate supports correspondingly different
community types. The effects of temperature and
sediment type on community composition are
difficult to separate, since they change concurrently
in the passage from the coastal to the mid-shelf
regime.
To this point, discussion has been limited to large-
scale trends evident across the shelf and has been
based on the assumption that a stable benthic com-
munity exists and has been surveyed at each station.
In fact, no data support the existence of stable ben-
thic communities in any but the broadest of senses.
The most significant results of this study are perhaps
of another scale entirely. Station groups outlined in
Figs. 63-4a, b, and c have perimeter dimensions that
span, at IGl, MSGA, and MSGB, nearly the length
(600 km) and a third (100-300 km) of the width of
the study area. Until now investigations of variation
in both biotic and abiotic provinces have been rela-
tively coarse grained, primarily due to the need for
baseline data. One consequence of this approach is
that our conception of small-scale and temporal
variation is unclear. Given the very gradual depth
change, gradual variation of sediment characteristics
within station groups, and internal consistency of
water-mass characteristics (temperature and salinity)
within major groups (i.e., between frontal zones),
groups denoted must be considered fairly homo-
geneous in their physical environment. Stations
spaced systematically across a completely homo-
geneous environment might be expected to show
nearly random affinities in the results of a clus-
ter analysis. Followed to an extreme, this reasoning
predicts that stations 5 km apart should have a proba-
bility of being clustered together equal to that of
being clustered with neighbors 100-500 km away.
On the contrary, such random linkages are ex-
ceptional (see dendrogram. Fig. 63-3). Nearly half
(15 of 31) of the stations sampled twice (permitting
an assessment of spatial variability assuming no
significant community change over the sampling
interval of one year) are found to be most similar to
the station closest in space, or to almost adjacent
stations. Whenever this trend does not hold, it is
impossible, given our lack of knowledge of the age-
structure of the population and population dynamics
in general, to separate temporal from spatial varia-
tion. However, in very similar pairs of stations
(1976 samples repUcating those of 1975), yearly
change must have been slight, and spatial patterns on
a smaller scale than that used to establish the station
grid are recognizable.
The implications of such small-scale patterning
are diverse. If the discontinuities between individual
stations are slight, the observations may simply have
resulted from sampling along gradients of continual
change in depth, sediment type, or some variable
not considered. Evidence indicating that these
transitions may be abrupt is found in Fig. 63-5, in
which order-of-magnitude contrasts in standing
Infaunal communities 1101
stock are seen between adjacent stations of the same
station group. When strong between-station dis-
continuities are found, it becomes important to
determine whether or not these are persistent features
in the area. Persistent dissimilar communities or
patches within the same physical and geographical
regime may be stable points (Sutherland 1974) or
elements of a temporal mosaic representing unstable
successional stages (Johnson 1970). There are no
means of resolving such disparate views of the shelf
without a knowledge of either the history or the
future of the communities that have been observed.
The answers to some of the questions posed may
require consideration of a broader class of commun-
ity attributes than that given here. As Ki^rboe
(1979) points out, a clear picture of temporal varia-
tion requires information on the role of stochastic
variation within single, stable community types; the
same is true of studies of spatial variation. Mills
(1975) has called for the examination of age/size
structure of individual species as imperative in the
study of the effects of predation. This is of further
importance as individuals of different sizes assume
different roles within the community or acquire
varying susceptibilities to predation.
SUMMARY
ACKNOWLEDGMENTS
This study. Contribution No. 430, Institute of
Marine Science, University of Alaska, Fairbanks, was
supported under contract #03-5-022-56 between
Howard M. Feder, the University of Alaska, and
NOAA, Department of Commerce, through the Outer
Continental Shelf Environmental Assessment Program,
to which funds were provided by the Bureau of Land
Management, Department of the Interior.
The investigation was made possible through the
efforts of the taxonomic staff of the Marine Sorting
Center, Institute of Marine Science, University of
Alaska, and particularly through the expertise of
Mr. George MueUer, Mr. Ken Coyle, Ms. Nora Foster,
and Ms. Kris McCumby. Mr. Grant Matheke offered
free access to an extensive library of computer pro-
grams and to a much-appreciated critical ear as well.
The study was a part of the work undertaken in the
pursuit of a Master's degree at the Institute of Marine
Science, University of Alaska, and I especially thank
Dr. H. M. Feder for undertaking the role of chairman
of my graduate committee.
The southeastern Bering Sea shelf may be divided
into at least four distinct faunal domains. An inshore
community is found in nearly all areas to a depth of
50 m, where the sharp transition from sand to silty
sand is accompanied by a marked community change.
This boundary coincides with a frontal zone at the
transition from coastal to mid-shelf water domains.
A less obvious faunal change seems to occur at 100
m, again in the passage through a frontal domain
separating Bering Sea/Alaska Stream water from
resident shelf water. The fourth domain is found
at the head of Bristol Bay in gravel and sand sub-
strates.
Although some species were found to be ubiqui-
tous, habitat preference was marked for many of the
species surveyed; most often, however, it is still
unclear whether the response is to temperature,
substrate type, or some other variable.
Standing stock is generally low, with the excep-
tion of nearshore patches along the Alaska mainland
and a localized mid-shelf area southeast of the
Pribilof Islands.
Changes in community type are often recognizable
over relatively short distances (100 km). Whether
these variations are stable or elements of a fluctuat-
ing temporal mosaic remains undetermined.
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Quantitative distribution of benthos
on the shelf and upper continental
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tions in the Northeast Pacific, P. A.
Moiseev, ed., 1:143-217, (Israel Prog.
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Age of bivalve mollusks and the
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J. E. Reeves, and R. G. Bakkala
Demersal fish and shellfish resources
of the eastern Bering Sea in the
baseline year 1975. Nat. Mar. Fish.
Serv., Northwest Alaska Fish. Cent.,
Proc. Rep.
Mathematical ecology,
and Sons, N.Y.
John Wiley
Semenov, V. N.
1964 Quantitative distribution of benthos
on the shelf of the southeastern
Bering Sea. In: Soviet fisheries
investigations in the northeast Pacific,
P. A. Moiseev, ed., 3: 167-75. (Israel
Prog. Sci. Transl., 1968.).
Skalkin, V. A.
1963
Stoker, S. W.
1978
Diet of flatfishes in the southeastern
Bering Sea. In: Soviet fisheries investi-
gations in the Northeast Pacific, P. A.
Moiseev, ed., 1:235-50. (Israel
Prog. Sci. Transl. 1968.)
Benthic invertebrate macrofauna of
the eastern continental shelf of the
Bering and Chukchi Seas. Ph.D.
Dissertation, Univ. of Alaska.
Sutherland, J. P.
1974 Multiple stable points in natural
communities. Amer. Nat. 108:859-
73.
Williams, W. T., and J. M. Lambert
1961 Multivariate methods in plant ecology,
II: Inverse association analysis. J.
Ecology 49:717-29.
Williams, W. T., and G. N. Lance
1977 Hierarchial classificatory methods./??;
Statistical methods for digital com-
puters, C. Enslein, A. Ralson, and
H. S. Wills, eds., 269-95. Wiley Inter-
science, N.Y.
Williams, W. T., and W. Stephenson
1973 The analysis of three-dimensional
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marine ecology. J. Experimental Mar.
Biol, and Ecol. 11:207-27.
Disturbance and Diversity
in a Boreal Marine Community:
The Role of Intertidal Scouring by Sea Ice
Charles E. O'Clair
Northwest and Alaska Fisheries Center,
Auke Bay Laboratory
National Marine Fisheries Service, NO A A
Auke Bay, Alaska
ABSTRACT
The intertidal region of most shores in the eastern Bering
Sea north of 56° N is subject to scouring by sea ice in late
winter and spring of most years. Using data collected with
systematically sampled belt transects and arrays of randomly
placed quadrats, intertidal communities on rocky shores in the
Pribilof Islands, frequently scoured by ice, were compared
with intertidal communities on rocky shores of islands in the
southeastern Bering Sea that are rarely scoured by ice.
Species richness (number of species in a community)
tended to increase with time from the last scouring episode.
In late spring of 1976, one month after sea ice left the Pribilof
Islands, species richness of most major taxa of plants and
invertebrates was significantly lower than in the previous year
four months after the last scouring episode. Species richness
at the Pribilof Islands was significantly lower than at Amak
and Akun islands (whose shores had not been recently scoured
by ice). Species-area curves of Mollusca only for the Pribilof
Islands leveled off at fewer species than did species-area curves
for Amak and Akun islands. Curves of the distribution of
biomass among species of Mollusca showed a greater concen-
tration of dominance among a few species in the Pribilof
Islands than at Amak and Akun islands.
Fugitive species of algae had the greatest wet weight in
most quadrats at the Pribilof Islands, whereas canopy species
were preponderant on unscoured shores. The biomass of
ephemeral algae and of known consumers of ephemeral algae
was about the same at all sites. Sessile invertebrates were
usually absent or small and low in abundance on unprotected
surfaces at the PribUof Islands.
Intertidal organisms find refuge from ice scour primarily
in crevices in bedrock and spaces beneath and between
boulders. The effect of perturbations on the intertidal
community structure will depend largely upon the degree
to which the refuge is altered in such a way as to exclude
marine organisms.
INTRODUCTION
Disturbance frequently controls local patterns of
species diversity. As used here, disturbance is an
event that results in abrupt, community-wide popula-
tion reductions independent of density and species.
Models relating disturbance and diversity (Grime
1973, Levin and Paine 1974, Horn 1975, and Connell
1978) generally predict that diversity will be greatest
at some intermediate level of disturbance. High and
low frequencies or magnitudes of disturbance result
in lower diversity. High levels of disturbance prevent
late-arriving and slow-growing species from invading
the community; low levels of disturbance allow the
community to develop to a low-diversity state of
competitive equilibrium.
Huston (1979) has proposed a general model of
species diversity built on the graphical models of
Grime (1973) and Connell (1978), but incorporating
the rate of competitive displacement as a funda-
mental parameter. Although most models have
assumed that ecological succession is operating in the
system, disturbance at some magnitudes greater than
zero may also maintain diversity in nonsuccessional
communities (Woodin and Yorke 1976).
The general predictions of the models relating
disturbance and diversity have been supported by
empirical evidence from a variety of environments
(Levin 1976 and Connell 1978 give access to the
literature; see also Fox 1979). Most systems studied
have been spatial or temporal mosaics created by
localized disturbance (see Levin 1976 for review) or
systems in which the successional trajectory of
community structure is severely deflected by infre-
quent disasters or catastrophes, such as fires (Loucks
1970), hurricanes (Connell 1978), submerged lava
flows (Grigg and Maragos 1974), and unpredicted low
tides (Loya 1976). In studies of chronically and
1105
1106 Benthic biology
severely disturbed communities, the disturbance has
usually been a result of human activities (Woodwell
1970, Grime 1973). Here I report the effects of a
widespread, frequent, and severe natural disturbance
(ice scour) on species diversity in a rocky intertidal
community.
McRoy and Allen (1974) have reviewed the avail-
able literature on ice-stressed coasts. Faunal surveys
(Madsen 1936, Vibe 1950) and descriptions of the
patterns of intertidal zonation in arctic and subarctic
regions (Stephenson and Stephenson 1954, Ellis and
Wilce 1961) have shed some light on how ice affects
intertidal populations, but there is little information
available on the role of ice scour in shaping the
structure of rocky intertidal communities.
The Pribilof Islands provide a useful system for
studying the effects of ice scour on a marine com-
munity for the following reasons: (1) the shores of
the Pribilof Islands are scoured by sea ice in most
years; (2) because they are near the southern limit of
sea ice, marine communities on the Pribilof Islands
can be compared to marine communities on islands at
about the same latitude that are ice free the year
round; and (3) since the Pribilof Islands are far
offshore and isolated from the influence of fresh
water from the major rivers of Alaska, the effects of
ice scour can be studied separately from the effects of
greatly fluctuating salinities.
In this chapter, I examine the effects of ice scour
on intertidal community structure by comparing
communities on the Pribilof Islands (St. George and
Otter islands) whose shores are frequently scoured by
sea ice with communities on islands at a similar
latitude whose shores are rarely (Amak Island) or
never (Akun Island) scoured by sea ice, and discuss
the effect of an oil spill on a community disturbed by
ice scour.
METHODS
I used data collected in 1975 and 1976 at Otter
Island and St. George Island in the Pribilofs and at
Amak and Akun islands near the Alaska Peninsula
(Fig. 64-1, Table 64-1) to test the effects of ice
scouring on intertidal communities. Data were
collected under the auspices of the Outer Continental
Shelf Environmental Assessment Program (OCSEAP).
Four sampling methods were used in this study:
transects, two random-sampling methods, and selec-
tively placed quadrats. Transects were laid roughly
perpendicular to the shoreline and were sampled at
regular intervals. They usually extended from the
level of mean higher high water or above to the
water's edge at low tide (Table 64-1). The number of
^^ urn
1
^r i
ST. PAUL ISLAND
"--OTTER ISLAND
"'5' ^'""^-VST. GEORGE ISLAND
Zapadni Bay 1
Garden Cove
J
^
4
AMAK ISLAND S!TE^
#^>s
^*
::\.:
_
_
Figure 64-1. Location of study sites.
transects at each site and the sampling interval (1-4
m) on each line depended on the slope, width, and
topography of the beach and the amount of time
available for sampling.
The transects were sampled with 1/16-m^ quad-
rats. The area within each frame was photographed
to record the coverage of obvious organisms. AU
organisms visible to the unaided eye were scraped
from the rock, placed in plastic bags, and fixed in 10-
percent Formalin. The abundance of an organism
that could not be adequately scraped from the rock
(e.g., a thin film of diatoms) was estimated visually in
situ.
One random-sampling method (random [A] in
Table 64-1) was used primarily on vertical or nearly
vertical surfaces such as the sides of large boulders
and rock outcrops. A facsimile of the area to be
sampled and the general pattern of distribution of
dominant organisms was sketched on a sheet of Mylar
plastic. Several (usually three) strata corresponding
to major biotic zones on the rock were outlined on
the sheet. One hundred numbered, uniformly dis-
tributed dots were then drawn on the sheet. The
positions of a fraction (usually about one-fourth) of
the dots were selected from a random number table.
The locations on the rock surface corresponding to
the randomly selected dots were marked with num-
bered arrows. A quadrat frame (1/16 m^ ) was then
placed at the tip of each arrow, photographed, and its
elevation determined. Since this sampling method
was originally adopted to follow changes in the biota
of the quadrats over time, no organisms were re-
moved from them. Plots of the same size with similar
biological cover in a nearby area were scraped clean
of organisms that were then collected and fixed.
The other random-sampling method (random [B]
in Table 64-1) was used only with the transects at
Otter Island in 1976. A quadrat (1/16 m^ ) was
I
Intertidal scouring by sea ice 1107
TABLE 64-1
Pertinent sampling information for study sites at Amai<, Ai<un, and the Pribilof Islands. Letters in parentheses indicate
sampling method: T, systematic transect; RA, random (A); RB, random (B); S, selected. Number in parentheses
indicates number of transects, arrow stations, etc., if more than one was established.
Tidal
range
Number
Latitude
Longitude
Substrate
Dates
sampled^
Sampling
of
Site
(N)
(W)
type
sampled
(cm)
method
samples^
Amak Island
55 24.1 163 09.3 bedrock/ 19 Jul 75
boulder
+222 to +17
transect
15
Akun Island
54°08.5' 165°38.7'
bedrock 18 Jul 75
+101 to +10 transect 17 (T)
random (A) 3 (RA)
Pribilof Islands:
Otter Island
57°02.9' 170°23.6'
boulder/
16 Aug 75
+85 to +9
transect (2)
22 (T)
bedrock
random (A)
3(RA)
12 Jun 76
+107 to +12
transect (2)
random (B)
10 (T)
3(RB)
St. George Island:
ZapadniBay 56°34.l' 169°40.3'
boulder/ 15 Aug 75
bedrock
+88 to +39 transect
High Bluffs 56°36.4' 169°49.9'
Garden Cove 56°33.8' 169°31.l'
boulder 13 Jun 76
becrock 9 Jun 76
+98 to 0 transect (2) 7 (T)
selected 1 (S)
+107 to +12 transect (2) 8 (T)
selected 7 (S)
^Zero tide level is mean lower low water.
^Surface area of all quadrats was 625 cm^ .
placed at a randomly selected distance from each
quadrat on the transect and at the same tidal level.
The randomly placed quadrats were sampled in the
same way as those on the transects.
Because of the paucity of biota on the transects at
High Bluffs and Garden Cove, 1/16-m^ quadrats were
placed at arbitrarily selected spots on rock surfaces
with obvious biotic cover. These selectively placed
quadrats were sampled in the same way as those on
the transects.
The elevations of samples taken by all methods
were determined with a transit and level rod using
standard surveying techniques. The reference level
was the level of low tide predicted in the tide tables.
At the predicted time of low tide, the level of the
water's edge was read. This elevation was assumed to
be the elevation predicted in the tide tables (NOAA
1976) for the nearest subordinate reference station
(e.g.. Trident Bay, Akun Island).
All samples were sorted by the Alaska Marine
Sorting Center of the Institute of Marine Science,
University of Alaska. All dominant organisms were
identified, counted (except when individuals could
not be readily distinguished, as happened with many
species of algae, sponges, and bryozoans), and
weighed (wet weight and dry weight— algae were not
weighed dry if wet weight was less than 1 g). Organ-
isms from most major phyla were identified to
species. Invertebrates from the following taxa were
not usually identified below the level of order:
Porifera, Cnidaria, Platyhelminthes, Nemertea,
Nematoda, Oligochaeta, Copepoda, Tanaidacea,
Insecta, Arachnida, Acarina, Sipuncula, Bryozoa, and
Ascidiacea. Counts and weights of mussels were
recorded separately for two or three size categories.
When 20 percent or more of the sample contained a
diverse mass of small biotic fragments, individuals
were counted in three small subsamples.
1108 Benth ic b iology
The size of the subsample was determined by
counting the number of species in the sample. If the
number exceeded 30, the sample was split in half, and
the number of species in one subsample was counted.
If the number of species in the subsample exceeded
30, the subsample was split in half. This procedure
was continued until a subsample containing 30 or
fewer species was obtained. Counts and weights of all
individuals of each species were extrapolated to the
entire sample by dividing the value for the subsample
by the ratio of subsample to sample wet weight.
All samples were collected from upper rock sur-
faces where the effects of ice scour are likely to be
most pronounced; habitats sheltered from ice scour
were not sampled.
None of the samples taken for laboratory analysis
were collected strictly at random. Whenever possible,
to minimize bias in statistical tests, I have chosen
at random a subset of the entire set of samples taken
at each site. Quadrats placed at arbitrarily selected
spots were not used in the statistical analysis.
The Zapadni Bay site was near a small northern fur
seal (Callorhinus ursinus) rookery. (Counts of adult
seals ranged from 222 to 249 at the Zapadni Bay
rookery in June and July 1978: Marine Mammal
Division 1979.) None of the other sites included in
this chapter were near fur seal rookeries, nor were
there large concentrations of northern sea lions
(Eumetopias jubatus) or harbor seals (Phoca uitulina)
at these sites during the sampling period (T. R.
Merrell, Jr., personal communication, 1979). It
seems unlikely that the diversity of intertidal organ-
isms at our sites was significantly affected by the
activities of marine mammals.
SPATIAL AND TEMPORAL DISTRIBUTION
OF SEA ICE
The Pribilof Islands are near the southern limit of
sea ice in the Bering Sea. Wise and Searby (1977)
computed semimonthly means of the position of
the edge of pack ice from data contained in Naval
Oceanographic Office annual reports in the years
1954-70. The authors show the Pribilof Islands at the
southernmost latitude of 15-day means of the pack-
ice edge in Februeiry through April. During the same
period, Amak and Akun islands were south of the
extreme southern limit of the pack-ice edge in all
months of the year; however, Amak Island was near
the extreme southern limit from February through
April.
I used Southern Ice Limit Charts (Department of
the Navy 1975, 1976) (Table 64-2) to determine
sea-ice conditions in the Bering Sea in five winters
(1972-76) just before and during our field studies
there. The charts are drawn primarily from satellite
imagery supplemented by conventional observa-
tions.' The Pribilof Islands were surrounded by pack
ice four of five winters before and during our field
studies. In the winter of 1973, when the Pribilof
Islands were ice free, St. Paul Island was very near
the southern limit of ice in late April. In three years,
1972, 1974, and 1976, the southern limit of ice was
near Amak Island.
Frequency and magnitude of disturbance
by pack ice
Pack ice frequently scours the Pribilof Islands and
probably causes widespread and severe physical
disturbance to intertidal communities. In recent
years, pack ice has occurred almost annually
in the Pribilof Islands; hence its occurrence is fre-
quent compared to the lifespan of most ecolog-
ically important inhabitants of intertidal communities
there.
Pack ice surrounds the Pribilof Islands in late
winter and early spring (Table 64-2). Although spring
tides are of greatest amplitude in early winter and
early summer, tidal fluctuations during late winter
and e£irly spring are large enough to allow all but the
highest intertidal levels to be scoured by ice. More-
over, when the islands are surrounded by pack ice,
presumably most of the shoreline is affected by
scouring. Scouring, therefore, is a widespread dis-
turbance both horizontally and vertically in the
Pribilof Islands.
Since many of the dominant organisms in intertidal
communities are sedentary, they can retreat neither
into crevices in bedrock nor into the interstices of
boulder fields, nor can they migrate to lower levels to
avoid being crushed or scraped from the substrate by
sea ice. The removal of large numbers of dominant
organisms from surfaces exposed to scouring severely
disturbs the organization of an intertidal community.
THE ROLE OF ISLAND BIOGEOGRAPHY
In terrestrial systems, species richness (the number
of species in the community) on oceanic islands
depends on and is usually reliably predicted by
the size of the island and its distance from the nearest
mainland area— factors that affect the rates of immi-
gration and extinction of potential or actual island
colonists (MacArthur and Wilson 1963, 1967).
Although field experiments in the marine environ-
* Conventional observations include those obtained from
ships, shore stations, and aerial reconnaissance.
Intertidal scouring by sea ice 1 109
TABLE 64-2
Sea ice at the Pribilof Islands and Amak Island in the winters of 1972 through 1976
(data from Department of the Navy 1975, 1976)
Year
Dates of first
and last ice^
Pribilof Islands
Total days
in ice*^
Highest coverage
(Oktas)'^
Amak Island
Dates of first Total days Highest coverage
and last ice^ in ice (Oktas)
1976
10 Feb., 4 May
75 (88) 6-8
1975
18 Jan., 1 Apr.
21 (28) 6-8
1974
26 Feb., 23 Apr.
18(22) 6-7
1973
Ice-free
(St. Paul near ice
edge
on 24 April 1973)
1972
13 Mar., 24 Apr.
32 (49)
7-8
23 Mar., 27 Apr. 21
Ice-free
26 Feb., 26 Mar. 25
(Amak at ice edge)
Ice-free
13 Mar., 27 Mar. 14
7-8
5-7
1-3
^Islands were not necessarily always in ice between the first and last dates of the period.
^Numbers without parentheses are the number of days St. George Island was in ice; numbers in parentheses are the number
of days St. Paul and Otter islands were in ice.
'^Amount of ice cover in eighths.
ment generally tend to support MacArthur and
Wilson's theory, at least one study (Schoener et al.
1978) contradicts their simple linear model. Fur-
thermore, the Mac Arthur-Wilson model has been
tested on patches of environment (not true islands),
such as plastic mesh sponges (Schoener 1974a), slate,
wood, or asbestos panels (Schoener 1974b, Osman
1978), and rocks (Osman 1978)— none with a surface
area of more than 2,500 cm^ .
For the following reasons, I assume that, compared
to ice scouring, island size and distance from the
source area (mainland Alaska) have a minimal effect
on differences in within-habitat species richness
between Akun, Amak, and the Pribilof Islands:
1. Oceanic currents may influence the direction
and rate of transport of marine propagules so as
to reduce differences between immigration rates
from source areas to near islands and to far
islands. Surface currents probably influence
the dispersal of propagules from intertidal areas
more than subsurface currents. The Bering
Slope Current (Kinder et al. 1975), a surface
current, could transport marine propagules by a
reasonably direct route to the Pribilof Islands
from the Alaska Peninsula and the eastern
Aleutian Islands. The mean velocity of this
current is low and produces a weak drift
(~ 5 cm/sec) toward the northwest from
Unimak Island (Kinder et al., in press). Never-
theless, a passively drifting organism leaving the
shores of the tip of the Alaska Peninsula or the
eastern Aleutian Islands could reach the Pribilof
Islands (400 km to the northwest) in about
three months.
Thorson (1950) has estimated that 55-65 per-
cent of the species of benthic marine inverte-
brates in boreal seas have a long pelagic larval
life (two to four weeks in summer, one to three
months in winter). Although according to
Thorson 's (1961) review fewer than 10 percent
of invertebrates with pelagic larvae have a larval
life longer than three months, recent work
(Strathman 1978) indicates that the maximum
length of larval life of planktotrophic species
may be much greater than was previously
thought. Moreover, the larvae of many inter-
tidal invertebrates can delay metamorphosis up
to five or six weeks if they do not find an
appropriate settling substrate (Day and Wilson
1934, Wilson 1948, Bayne 1965, and Thorson
1966). The larvae of Mediaster aequalis, a
subtidal seastar, can postpone metamorphosis
for up to 14 months if their preferred substrate,
Phyllochaetopterus prolifera tubes, is absent.
Mediaster set successfully when offered Phyl-
lochaetopterus tubes at the end of this period
(Birkeland et al. 1971). It seems likely that
potential colonists from the Alaska Peninsula, at
least many benthic invertebrates, arrive at the
Pribilof Islands frequently, perhaps yearly.
1110 Benthic biology
2. The amount of rocky intertidal habitat (area of
shore) on even the smallest island that I studied
is immense compared to the body size of most
intertidal organisms at the islands. Therefore,
the ratio of habitable island area to organism
size is much greater for intertidal biota than it
would be for terrestrial plants, birds, mice, or
lizards on islands of comparable size.
In the present study, I assume that rates of extinc-
tion are not significantly related to the size of the
islands. Support for this assumption comes from a
comparison of species richness at a large versus a
small island in the Pribilof Islands. Otter Island is
slightly farther from the nearest mainland source area
than St. George Island, but its habitable area (as
approximated by island periphery) is 1/14 that of St.
George Island. Nevertheless, species richness of
benthic biota at Otter Island consistently equaled or
exceeded that at St. George Island (see results sec-
tion).
THE ROLE OF PHYSICAL FACTORS
Differences in physical factors other than ice
scouring (e.g., temperature and salinity) among
islands were probably not great enough to cause
significant differences in species diversity. Amak
Island, Akun Island, and the Pribilof Islands are all
within the Aleutian (biogeographic) Province
(Valentine 1966, Briggs 1974). Although the bound-
aries of marine biogeographic provinces are usually
defined by biotic criteria, there is strong evidence to
indicate that they are determined by physical factors,
especially temperature, salinity, and major currents
(Pielou 1979). Therefore, organisms at the islands
that I studied are probably exposed to similar regimes
of temperature and salinity.
Temperature is generally considered to be the chief
factor controlling the geographical distribution of
marine organisms (Orton 1920, AUee 1923, Hutchins
1947, and Hedgpeth 1957). Golikov and Scarlato
(1973) have adopted Hutchins's (1947) scheme for
defining the geographical limits of distribution of
marine organisms on the basis of water temperature
and have applied it to seven biogeographical groups of
coastal moUusks. The Pribilof Islands, Amak Island,
and Akun Island fall within the temperature limits of
three of their biogeographical groups: Pacific-widely-
distributed-boreal species. Pacific-high-boreal species,
and boreo-arctic species. The northern limit of
geographical distribution is set by summer maximum
and winter minimum temperatures (Hutchins 1947).
According to Golikov and Scarlato (1973), summer
temperatures must reach 8 C for species in the first
two groups listed above to reproduce; summer
temperatures must reach —0.4 C for species in the
boreo-arctic biogeographic group to reproduce.
Golikov and Scarlato (1973) set the minimum tem-
perature for survival rather vaguely at temperatures
less than 0 C for all the biogeographic groups.
Mean and extreme summer water temperatures at
all the islands that I studied were above 8 C (Table
64-3). Average winter water temperatures were
above and minimum water temperatures were slightly
below 0 C at all islands. Long-term seasonal means of
salinity were almost identical in summer and winter
at all islands considered here (Table 64-3).
Summer and winter air temperatures tended to
decrease with higher latitude, but mean and maxi-
mum summer temperatures at all islands generally
remained above those necessary for reproduction of
species in the three biogeographic groups likely to
have representatives at any of the islands (Table
64-3). Winter air temperatures were somewhat lower
at the Pribilof Islands than at Amak and Akun
islands, but we do not have enough information on
tolerance to cold in benthic plants and invertebrates
from the Bering Sea to know whether winter temper-
atures at the Pribilof Islands were low enough to
reduce species richness significantly.
Following Golikov and Scarlato's (1973) classifica-
tion, I determined the relative contribution of the
three biogeographic groups discussed above (boreo-
arctic species, Pacific-widely-distributed-boreal spe-
cies, and Pacific-high-boreal species) to the molluscan
fauna of the Pribilof Islands, Amak Island, and Akun
Island (Table 64-4). O'Clair et al. (Appendices IIB
and lie, 1979) list the species of mollusks at each of
these islands. Species whose ranges extend from the
Bering Sea to California but not to Asiatic shores
were included in the Pacific-widely-distributed-boreal
group.
Most mollusks at all islands were Pacific-high-
boreal species. The Pribilof Islands harbored one
more boreo-arctic species and one fewer species
ranging as far south as California (i.e., Pacific-widely-
distributed-boreal species) than the southernmost
island (Akun Island) in this study. When I compared
the list of molluscan species found in this study with
that compiled by Dall (1899) for the Pribilof Islands,
I found that 30 percent of the mollusks in the
present study recorded at Akun Island but not at the
Pribilof Islands and 55 percent of the species recorded
at Amak Island but not at the Pribilof Islands have
been found at the Pribilof Islands by other workers
(Dall 1899). The distribution of benthic mollusks
among biogeographic groups was similar at the
Pribilof Islands, Amak Island, and Akun Island (Table
Inlertidal scouring by sea ice 1111
)
64-4), and lists of species of mollusks at these islands
are similar in composition; therefore, differences in
species diversity among islands probably do not come
from differences in temperature regimes that prevent
species from persisting at the Pribilof Islands but
allow them to inhabit the shores of Amak and Akun
islands.
SPECIES DIVERSITY AT SCOURED
AND UNSCOURED ISLANDS
To examine the effect of ice scouring on intertidal
community structure, I used two community attrib-
utes: species richness and the distribution of impor-
tance among species. These two attributes were used
to compare intertidal communities on upper rock
surfaces in the Pribilof Islands with intertidal com-
munities in similar habitats at Amak and Akun
islands.
Species richness
Species richness was approximated by average
species densities (the average number of species in
1/16-m^ quadrats at similar intertidal locations)
of most major taxa of benthic plants and inverte-
brates and by species-area curves for MoUusca only.
The following taxa are excluded from the analyses
of species densities because organisms in them were
usually not identified below the level of order:
Porifera, Cnidaria, Platyhelminthes, Nemertea, Oligo-
chaeta, Nematoda, Copepoda, Tanaidacea, Insecta,
Arachnida, Acarina, Sipuncula, Bryozoa, and
Ascidiacea.
Average species densities on rock surfaces of the
different islands tended to increase with longer time
since the last ice-scouring event (Fig. 64-2). I tested
the significance of these results with a two-way
analysis of variance (anova). Because the cell means
were approximately equal to their respective vari-
ances, the counts were transformed ([x + 0.5]'^').
Bartlett's test revealed that the variances of the
transformed counts were homogeneous (P = 0.22).
The anova revealed that the treatment means
(among islands and between intertidal levels) were
from different populations (Table 64-5). Because the
interaction term was not significant, orthogonal
comparisons were made of means of species densities
in the upper and lower intertidal zones combined
(Table 64-5). Because the mean of densities from the
Pribilof Islands (St. George and Otter islands com-
bined) in 1976 was significantly less (P < 0.05) than
in 1975, I compared only the 1975 data from the
Pribilof Islands with the 1975 data from Amak and
Akun islands combined. The difference between
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1112 Benthic biology
TABLE 644
Relative contribution of three biogeographic groups to the molluscan fauna of the Pribilof Islands, Amak Island,
and Akun Island
Number and percentage of species^
Location
Boreo-arctic
No. %
Pacific-widely-distributed-boreal
No. %
Pacific-high-boreal
No. %
Amak Island
5
24
7
33
9
43
Akun Island
7
25
10
36
11
39
Pribilof Islands
8
28
9
31
12
41
'Lists of species of mollusks at each location were taken from appendices IIB and IIC of O'Clair et al. (1979).
>
(/)
Z
LJJ
Q
W
UJ
O
LU
0_
W
25
20
15
10
_ 1976
■ ST. GEORGE I.
• OTTER I.
A AMAK I.
Open Symbol - Upper Intertidal Data
Closed Symbol - Lower Intertidal Data
1975
A
40
30
20
10
_L
_L
J_
_L
AKUN I.
<>
3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 UNSCOURED
MONTHS SINCE LAST SCOURING EVENT
Figure 64-2. Relationship between mean species density and time since last scouring event at the Pribilof Islands (1975 and
1976), Amak Island (1975), and Akun Island (1975). Vertical lines represent standard deviation. Open symbols = upper
intertidal data; closed symbols = lower intertidal data.
means of species densities at the Pribilof Islands and
means of species densities from Amak and Akun
islands was highly significant (P < 0.001). Species
densities at Amak Island were significantly less (P <
0.001; Table 64-5) than those at Akun Island.
I chose Mollusca to compare species-area relation-
ships in the intertidal region at Amak and Akun
islands and the Pribilof Islands because Mollusca is a
diverse group of invertebrates with representatives at
all intertidal levels, and the Bering Sea fauna is
comparatively well known taxonomically. Other
diverse groups of intertidal organisms, such as
Rhodophyta, Polychaeta, and Gammaridea, are more
susceptible to the physiological stresses of the upper
intertidal environment and hence have few represen-
tatives at upper levels. The Bering Sea representatives
of these groups are not well known taxonomically.
Intertidal scouring by sea ice 1113
TABLE 64-5
Tests of significance of species densities of plants and invertebrates in tiie rocky intertidal region
at Akun, Amak, and the Pribilof Islands ^
Means of species
densities
Upper
intertidal area''
Lower intertidal area*=
Site
n
X
SD
n
X
SD
Pribilof Islands (?)
St. George Island
High Bluffs
2
1.5
0.7
5
4.4
2.2
Garden Cove
2
0.5
0.7
6
1.3
1.2
Zapadni Bay
2
0.5
0.7
4
7.2
3.4
Otter Island
1975
3
3.7
1.5
22
8.3
4.0
1976
4
4.8
2.5
9
8.4
5.0
Amak Island (Am)
3
11.0
7.0
12
16.3
8.1
Akun Island (Ak)
4
16.2
9.7
15
33.3
8.9
Anova*^
Source
d.f.
SS
MS
Intertidal level
Site
Level X Site
Error
1
6
6
79
13.1
88.5
1.1
47.3
13.1
14.7
0.2
0.6
21.8***
24.6***
0.9 ns
Comparisons of means
Comparison*^
Difference of means
SS
P 1975 vs. P 1976
P 1975 vs. Am and Ak
Am vs. Ak
3.3
4.3
1.5
3.4
56.5
19.6
5.6*
94.3***
32.7***
^SD = standard deviation, ns = not significant, * = 0.01<P< 0.05, *** = P< 0.001, SS=sums of squares, MS=mean squares,
F = Ratio of MS groups to MS error.
''Mean higher high water (MHHW) to mean tide level (MTL).
'^MTL to mean lower low water (MLLW).
'^Disproportionate sample sizes necessitated using the method of weighted squares of means to make inferences about main
effects.
^Orthogonal comparisons.
Eight quadrats were randomly selected from all the
sampled quadrats that fell in the range from mean
low water to just above mean high water at each
site. Only 1975 data were used for this and later
analyses in this chapter. The sample size for each site
was limited by the total number of quadrats (eight)
sampled in this tidal range at Amak Island. Sample
size appeared to be adequate for all sites except Akun
Island (Fig. 64-3). The cumulative species count for
Akun Island continued to climb as the number of
quadrats included increased to eight, but when seven
more quadrats were randomly added, the species
counts eventually leveled off at 31 species. Therefore,
it appears that even at the island with the most
species, Akun Island, the sample size included 87
percent of the species of mollusks on upper rock
surfaces in the intertidal zone.
The species-area curves for mollusks in the Pribilof
1114 Benthic biology
o
o
CO
UJ
o
LU
D.
CO
Lil
>
I-
<
_l
O
30
25
20-
AKUN ISLAND
AMAK ISLAND
OTTER ISLAND
ST. GEORGE ISLAND
4 5 6
NUMBER OF SAMPLES
10
Figure 64-3. Species-area curves of mollusks in quadrats collected in the intertidal region at four islands in the Bering Sea.
The shores of two islands (Otter and St. George) are frequently scoured by sea ice.
Islands leveled off at the lowest species counts (4 and
7; Fig. 64-3); the curve for Akun Island increased to
the highest count (27). The curve for Amak Island
reflected an intermediate species richness. Therefore,
the results of the comparisons of molluscan species-
area curves between islands paralleled results of the
species counts of most other major taxa (Figs. 64-2
and 64-3).
Species-importance curves
In order to examine the distribution of biomass
(wet weight) among mollusks, I used species-impor-
tance (=dominance-diversity) curves (Whittaker
1965, 1970, 1972). Species-importance curves are
constructed by plotting the importance (usually in
terms of abundance, biomass, coverage, or productiv-
ity) of a species on the ordinate (on a logarithmic
scale) opposite its rank in the measure of importance
selected on the abscissa, on which species are ranked
from most to least important. Whittaker (1965) has
found that, at least in terrestrial plant communities.
three of the measures of importance commonly used
by various authors, coverage, biomass, and produc-
tivity, produce species-importance curves which
differ in steepness but not in form. BatzU (1969) has
claimed that in the rocky intertidal region, biomass is
a better measure of importance than number of
individuals.
Three theoretical distributions of importance
among species occur frequently in the literature; May
(1975) relates them. The most uniform is the
broken-stick distribution, and the least uniform is the
geometric series; the lognormal distribution falls
between these two. The form of each distribution
when plotted as importance versus rank is shown in
May's Figure 1 (1975). Two of the distributions (the
broken stick and the geometric series) reflect, in
theory, biological mechanisms (types of competition)
that structure the community. The lognormal
distribution arises when species-importance relation-
ships are controlled by the "interplay of many
independent factors" (May 1975).
Intertidal scouring by sea ice 1115
Pielou (1975) argues that when the total number
of species present is being estimated by the data and
the community is small, as in the present study, one
cannot statistically test the fit of the observed data to
the theoretical distribution. However, we can test the
difference between the empirical distributions with
tests of the Smirnov type (Pielou 1975, Conover
1971).
Visual comparison of the species-importance curves
for Amak and Akun islands and the Pribilof Islands
showed that biomass of mollusks was most evenly
distributed among the species at Akun Island (Fig.
64-4). The curve for Akun Island appeared closest to
the lognormal distribution. The species-biomass
distributions become less and less uniform (i.e.,
toward a greater concentration of biomass among a
few dominant species) at Amak, Otter, and St.
George islands, in that order (Fig. 64-4). Eighty
percent of the wet weight was concentrated among
one or two dominant species at Amak, Otter, and St.
George islands, whereas five species shared 80 percent
of the wet weight at Akun Island. The curve for St.
George Island most closely approached the geometric
series distribution.
Using the Smirnov test, I tested only the species-
importance curves for St. George Island and for Akun
Island, because the Smirnov test and others like it
which can detect differences in the form of empirical
distribution functions are valid for situations involv-
ing more than two samples only if sample sizes are
equal (Conover 1971). Because n (sample size: the
number of points which determine the curve) for the
species-abundance curve is the number of species in
the collection and not the number of samples col-
lected, sample size cannot be controlled. Values
of n were unequal among the four sites.
The Smirnov test of the empirical distribution
function of St. George Island versus that of Akun
Island was not significant (T^ = 0.378, N^ = 5, N2 =
27). Presumably, this holds for comparisons between
islands with less divergent species-biomass distribu-
tions, as between Otter Island and Akun Island, or St.
George Island and Amak Island. This result is surpris-
ing because the curves appear markedly different
when compared visually (Fig. 64-4). The test is
conservative when the random variables are discrete,
and use of the asymptotic approximation for large
sample sizes further increases the conservatism
o
o
LU
>
UJ
DC
LU
O
CC
LU
Q.
100
10
1.0
0.1
0.01
0.001
0.0001
AKUN ISLAND
OTTER ISLAND
ST. GEORGE ISLAND
J I I L
J I L
J I I I I I I I I I I L
J I I L
10
15
20
25
30
SPECIES SEQUENCE
Figure 64-4. Relationship between relative importance (biomass expressed as a percentage on a logarithmic scale) and rank
of mollusks at four islands, the shores of two of which (Otter and St. George islands) are frequently scoured by sea ice.
1116 Benthic b iology
(Conover 1971). However, if differences in the form
of the curves reflect true differences in the distribu-
tion of biomass among species, it seems likely that
the Smirnov test would reject the hypothesis that the
St. George and Akun Island curves were the same
despite the test's conservatism. Species-importance
curves may be influenced by species richness to such
an extent that the distribution of importance among
species is obscured, especially when one compares
curves drawn from collections of species greatly
disparate in size.
EFFECTS ON COMMUNITY DOMINANTS
AND SUCCESSION
Ice that annually scours the intertidal region
frequently denudes the rocky substratum; therefore,
benthic communities would not be expected to
develop beyond the early stages of succession. One
might expect these communities to be composed of
species that colonize bare areas rapidly, such as
fugitive species (Hutchinson 1951), or species that
are able to take refuge during scouring episodes.
Conversely, species that normally colonize during
later stages of succession or that have no refuge, such
as sessile species, would probably be absent or low in
abundance where the frequency of scouring is high.
The earliest colonizers of denuded surfaces are
usually ephemeral algae such as diatoms, the filamen-
tous green algae (Spongomorpha spp.), fohose green
(ulvoid) algae, and some foliose red algae (Porphyra).
These species often have good powers of dispersal or
release propagules into the water the year round, but
they usually persist for no more than a few months
because they suffer in competition with other algae
for space or light (Dayton 1975) or are preferentially
grazed by herbivores (Lubchenco and Menge 1978).
Other fugitive algae, such as Halosaccion glandi-
forme, appear after the ephemeral species and are, in
turn, generally followed by a sequence of species with
lower powers of dispersal and slower growth rates.
Among this last group are most species of the genera
Alaria, Fucus, Hedophyllum, and Laminaria that
grow leirge, form a canopy over other members of the
community, and apparently dominate other algae in
competition for light and space (Dayton 1975).
These species usually dominate communities where
the frequency of disturbance is low.
At the times the sites were sampled, ephemeral
algae (species were designated ephemeral after
Appendix 1 of Lubchenco and Menge 1978) domi-
nated intertidal plots rarely at St. George and Otter
islands and never at Amak and Akun islands (Table
64-6). The number of species of ephemeral algae was
about the same at sites on Otter, Amak, and Akun
islands, but markedly lower (only Porphyra sp.
was present) at the site on St. George Island (Table
64-7). The filamentous green alga Spongomorpha
spinescens and the ulvoids Monostroma sp., M.
fuscum, and Ulua lactuca, absent from plots
collected at the Pribilof Island sites, were present at
Amak or Akun Island, or both (Table 64-7). Con-
versely, only Spongomorpha sp. and S. arcta were
present at a Pribilof Islands site (Otter Island) but
absent from samples taken at the Amak and Akun
Island sites.
The organisms that most frequently dominated
(had the greatest biomass in) the plots at the Pribilof
Islands sites were Halosaccion glandiforme and
Halosaccion sp. (I do not have conclusive evidence
that these species are truly ecologically dominant
over ephemeral algae in the sense that they preempt
the greatest share of a limiting resource. It seems
likely that, because Halosaccion spp. are larger than
most ephemeral algae, they would be more successful
in occupying space or intercepting light— two re-
sources that are likely to limit growth in intertidal
systems. However, other mechanisms such as selec-
tive herbivory may cause the apparent dominance of
Halosaccion spp. in this system.) Halosaccion glandi-
forme dominated half of the lower intertidal plots at
St. George Island. At Otter Island, H. glandiforme
dominated all of the upper intertidal plots; and with
Halosaccion sp., it dominated most (66 percent) of
the lower intertidal plots (Table 64-6). Neither
species dominated any plot at Amak or Akun Island,
but H. glandiforme was present in 30-50 percent of
all plots on both islands, except in the upper inter-
tidal zone at Akun Island (Table 64-6 and Fig. 64-5).
Halosaccion glandiforme is an annual. At
Amchitka Island, Alaska (midway along the Aleutian
Island chain), the spores of this species settle at
all times of year except winter, and the thalli grow
rapidly (Lebednik and Palmisano 1977). Dayton
(1975) classifies H. glandiforme as a fugitive species
on the outer coast of Washington, although appar-
ently it can settle and grow in the understory of a
"climax" community (Lebednik and Palmisano
1977). Since it can persist on the same site for
several years (Lebednik and Palmisano 1977), its
presence in the community does not necessarily
indicate that the community is at an early stage of
succession. However, it is unlikely that H. glandi-
forme could persistently dominate the community to
the apparent exclusion of the canopy species (Table
64-6) unless some mechanism prevented the canopy
species from settling among and growing over stands
of H. glandiforme.
Intertidal scouring by sea ice 1117
TABLE 64-6
Dominant (in biomass) species, frequency of dominance (D) and frequency of occurrence (F)
of each species in upper (upper number) and lower (lower number) intertidal zones at the islands studied.
Species^
St. George^
Otter
Amak
Akun
Island
Island
Island
Island
D F
D F
D
F
D
F
Spongomorpha sp.
Porphyra spp.
Halosaccion glandiforme
Halosaccion sp.
Alaria taeniata
Alaria sp.
Odonthalia floccosa
Fucus distichus
Littorina sitkana
Littorina sp.
25
50
0.75
1.0
0.25
28
0.75
—
0.5
25
1.0
50"
0.5
0.06
0.06
00
1.0
22
0.78
—
0.33
44
0.83
0.06
17
0.5
0.17
0.5
0.33
0.17
0.4
0.2
-
50
0.5
33
0.33
0.44
17
0.5
—
0.1
—
—
0.5
33
1.0
—
—
0.1
10
0.8
—
50
1.0
33
1.0
—
67
1.0
30
0.9
1.0
—
0.5
—
0.67
0.83
—
0.33
—
0.7
Balanus cariosus
0.33
60
0.67
0.9
^Data are in percentage of quadrats in which each species had the greatest wet weight. All species showing the greatest wet
weight in at least one quadrat/level/site combination are included. Dash means species was never dominant (D column) or was
absent (F column) at the particular level and site.
''Algae are listed roughly in order of increasing persistence in undisturbed environments.
'^Only two plots were sampled in the upper intertidal zone at St. George Island; one was bare.
Three species of canopy-forming algae— Fucus
distichus, Alaria sp., and A. taeniata— were present in
plots at the Pribilof Islands (Table 64-8). (Although
Laminaria longipes was not recorded in the quadrats
at the Pribilof Islands, it was often seen growing
between rocks there. Many fronds of this alga were
partly or completely sheared off where they emerged
from the rocks [N. Calvin, personal communication
1979] ). None of these species dominated plots at
St. George Island, although Fucus and Alaria sp. were
present in the lower intertidal zone. At Otter Island,
Alaria sp. or A. taeniata dominated some lower
intertidal plots but their biomass values were highly
variable (Tables 64-6 and 64-8).
The number of species, frequency of dominance,
and average wet weight of canopy species increased
from the Pribilof Islands to Amak and Akun islands.
At Amak Island, F. distichus and Alaria sp. domi-
nated (in biomass) plots in the upper intertidal zone
(Table 64-6). These two species and A. taeniata
dominated plots in the lower intertidal zone. Three
additional canopy species— Hedophy Hum sessile.
1118 Ben th ic b iology
TABLE 64-7
Ephemeral species^ and mean wet weight (x )*' in upper (upper number) and lower (lower number) intertidal zones at the
islands studied.'^
Species
St. George
Island
X SD
Otter
Island
SD
Amak
Akun
Island
Island
SD
X
SD
Spongomorpha sp.
0.003
0.01
S. arcta
1.3
3.7
S. spinescens
1.0
0.008
1.4
0.02
Monostroma sp.
1.3
4.0
M. fuscum
0.01
0.03
3.1
7.8
Ulva lactuca
0.2 0.6
Pylaiella littoralis
0.01
0.05
0.4 0.8
Scytosiphon lomentaria
Porphyra spp.
0.3
9.1
15.8
.009
0.9
0.04
0.6
18.2
15.2
1.4
26.2
37.2
^Species of algae were designated ephemeral from Appendix 1 of Lubchenco and Menge (1978).
^Wet weight in g/625 cm^
*^Dash means species was absent from the particular level and site. SD = standard deviation.
Laminaria sp., and L. longipes — were found in lower
intertidal plots at Akun Island (Tables 64-6 and 64-8)
but were never predominant. (However, N. Calvin in
a personal communication in 1979 noted large areas
in the lower intertidal area at Akun Island where H.
sessile formed the canopy. These areas were not
sampled.) F. distichus, Odonthalia floccosa, and the
barnacle Balanus cariosus had the greatest wet weight
in lower intertidal plots at Akun Island. F. distichus,
O. floccosa, and Alaria sp. dominated upper plots
there.
COMPETITION, HERBIVORY, AND
SUCCESSION AFTER ICE SCOURING
Each year that ice scouring occurs, it sets back the
process of succession to an early stage by creating
bare rock that ephemeral species can colonize. In the
present study, four months after the last scouring
episode, Halosaccion spp. dominated most plots on
scoured islands; and Spongomorpha sp. and S. arcta
were the only ephemeral algae with greater biomass
on scoured islands than on unscoured isleinds (Tables
64-6 and 64-7).
Two mechanisms acting alone or in concert may
have allowed Halosaccion spp. to dominate plots on
scoured shores. In the first, Halosaccion spp. settle at
the same time as early-colonizing ephemeral species,
or later, and then simply outcompete the ephemeral
species for space or light. In the second, preferential
grazing by snails on ephemeral algae allows Halosac-
cion spp. to settle and grow without competition
from these algae. In New England, grazing by
Littorina littorea on ephemeral algae accelerates the
development of Chondrus crispus (Irish moss)
beds (Lubchenco and Menge 1978).
In tertidal scouring by sea ice 1 119
ALGAE
X
O
LU
I-
Ul
1,000
h-
I
100
(1
LU
10
^
1.0
1-
LLI
0.1
0
1,000
100
10
1.0 -
0.1 -
0
UPPER INTERTIDAL
_L
I
3
I Alaria sp.
2 " Alaria taeniata
3 ~ Fucus distich us 5 ~ Halosaccion sp.
4 " Halosaccion glandiforme
LOWER INTERTIDAL
3 3
1 1
i
-
1 3
4
1
5
1
2^
r ~\^
-, 4
'' r
1 4
2
-
t
rh
-.
rh
1
1
1
1 1
1
ST. GEORGE
ISLAND
OTTER
ISLAND
AMAK
ISLAND
AKUN
ISLAND
Figure 64-5.
intervals.
Mean weigiit of four species of algae at four islands in the Bering Sea. Vertical lines are 95-percent confidence
Although an unambiguous evaluation of the
relative roles of herbivory and competition on the
structure of these intertidal communities requires
experimental manipulation of populations of herbi-
vores and Halosaccion, the relationship of the abun-
dance of ephemeral algae and Halosaccion spp.
on scoured and unscoured surfaces to relative inten-
sity of herbivory may shed light on the mechanism
resulting in dominance of Halosaccion spp. at St.
George and Otter islands. I assumed that the inten-
sity of herbivory increased proportionately with the
biomass of herbivores.
The most abundant intertidal grazer in plots in
the intertidal zone at our Pribilof Islands sites was
Littorina sitkana (Fig. 64-6). Three other moUus-
can herbivores— //a/oconc/ia reflexa, Margarites heli-
cinus, and Schizoplax brandtii— were present in lower
intertidal plots at Otter Island but were smaller and
less abundant than L. sitkana. One Katharina tuni-
cata was found in a lower intertidal plot at St. George
Island. Littorina sitkana and L. aleutica were com-
mon in plots at Amak and Akun islands (Fig. 64-6).
Little is known about the food habits of Littorina
sitkana, nothing of those of L. aleutica. Caged L.
sitkana graze diatoms and probably the sporelings of
Ulva sp. and Enteromorpha sp. (Behrens 1971). Other
species of Littorina eat mainly diatoms (but see
Hayes 1929 and Berry 1961) and small, tender algae
(Table 64-9), which are usually ephemeral
(Lubchenco 1978). However, L. scutulata and L.
littorea also feed on large plants (Hayes 1929, Bakker
1959, Dahl 1964, Lubchenco 1978).
Limpets could also reduce the abundance of
ephemeral algae. Four species of limpets— Co//rse//a
sp., C. pelta, Notoacmea scutum, and N. persona-
were found at our study sites at Amak and Akun
islands. Limpets were absent from the intertidal
plots at St. George and Otter islands, but C. pelta was
found in 70 percent (n = 34) of the plots below mean
low water at St. George Island.
Notoacmea scutum, Collisella pelta, and other
limpets of the genus Collisella eat diatoms, blue-green
algae, and other microscopic algae (Castenholz 1961,
Haven 1973, Nicotri 1977), but their diets may
1120 Benthic biology
TABLE 64-8
Canopy species and mean wet weight (x )^ in upper (upper number) and lower (lower number) intertidal zones'' at
the islands studied
Species'
St. George
Island
Otter
Island
SD
SD
Amak
Island
X SD
Akun
Island
X SD
Fucus distichus
—d
0.08
Alaria taenia ta
—
Alaria sp.
3.6
Hedophyllum sessile
—
0.10
7.2
7.3
87.4
31.0
44.8
108.6
44.7
- 121.6
272.4 53.3
57.4
113.6
109.5
172.0
130.1
362.5
165.5
22.5
45.8
2.5
16.1
409.8
158.6
52.7
79.4
8.0
42.2
Laminaria longipes
lA
16.4
Laminaria sp.
0.09
0.3
^Wet weight in g/625 cm^
''Upper intertidal extended from mean high water to mean tide level (MTL).
Lower intertidal extended from MTL to mean low water.
*^Species were designated as canopy species after Dayton (1975) and Menge (1976).
'^Dash means species was absent from the particular level and site.
include a greater proportion of macroscopic algae
than those of Littorina spp. Acmaea pelta (= Colli-
sella pelta) ingests a wide variety of microscopic and
macroscopic algae, including small fragments of large
plants such as Pelvetia and Egregia (Craig 1968).
Walker (1968) concluded from a study of the config-
uration of the gut of Acmaea scutum (= Notoacmea
scutum) that it probably feeds mainly on large algae.
She also found fragments of flat encrusting algae in
its gut. I could find no information on the diet of N.
persona.
At the time of the present study, the intensity of
herbivory on ephemeral algae was apparently no
greater at Otter and St. George islands than at Amak
and Akun islands. The biomass of Littorina spp. was
significantly greater at the St. George and Otter
islands sites combined than at the Akun and Amak
islands sites combined (Table 64-10), but the lower
biomass of Littorina spp. at the Amak Island site
accounted for this difference (Table 64-10). There
was no significant difference between the average
biomass of Littorina spp. at St. George and Otter
islands and that at Akun Island.
The absence of limpets in the quadrats at the
Pribilof Islands may indicate fewer species of known
consumers of ephemeral algae on scoured surfaces
there. Haloconcha reflexa, Margarites helicinus, and
Schizoplax brandtii may ingest young sporophytes
and gametophytes of ephemeral algae while grazing,
but because they are smaller and less numerous than
L. sitkana on St. George and Otter islands, they
probably cannot control populations of ephemeral
algae on these islands.
Similar levels of Littorina spp. biomass at the
Pribilof Islands and Akun Island may be misleading.
Greater species richness and weight of large macro-
phytes at Akun Island (Table 64-8) resulted in
greater spatial heterogeneity and probably a greater
effective grazing area for Littorina spp. Therefore, the
biomass of Littorina spp. per unit of effective grazing
area may be much greater on frequently scoured rock
at the Pribilof Islands than on unsecured rock at
Akun Island. I have no measure of the effective
grazing area contributed by macrophytes at Akun
Island.
Finally, the data may reflect the results of herbi-
Inlerlidal scouring by sea ice 1121
X
UJ
Lil
1,000 -
100 -
10
1.0 h
0.1
0
SELECTED HERBIVORES
UPPER INTERTIDAL
I
5
3
JTLl
74
.. Hi
M
1 Collisella pelta
2 - Collisella sp.
3 - Littorina sp. 5 - Littorina sitkana I Notoacmea scutum
4 - Littorina aleutica D ~ Notoacmea persona
D)
%-•
I
O
I-
LU
1,000 -
100 -
10 -
1.0 -
0.1
0
LOWER INTERTIDAL
5
ST. GEORGE
ISLAND
5
rh
1
1
rli
7
1
5
_L
01
ISL
"T
.A
ER
ND
AM
ISL/
A
\N
<
D
AKUN
ISLAND
Figure 64-6. Mean weight of seven species of herbivores on ice-scoured (St. George and Otter islands) and unscoured
islands in the Bering Sea. Vertical lines are 95-percent confidence intervals.
vory when the intensity of herbivory was relaxed,
after the period when colonizing algae were settling
and growing most rapidly and consumers were
exerting their greatest effect. An evaluation of the
role of herbivores in community development on
rock surfaces scoured by ice awaits further study.
The populations of plants and herbivores in this
system are probably amenable to experimental
manipulation.
POPULATIONS OF SESSILE
INVERTEBRATES
Sessile invertebrates should be absent or low in
abundance (or wet weight) when the frequency of
scouring is high. Sessile invertebrates cannot retreat
under rocks or into crevices during scouring, and
most can recolonize scoured rock only by settlement
of planktonic larvae. My data tend to support the
supposition that populations on scoured surfaces are
probably represented solely by young individuals that
have settled since the last scouring event. Four
species— My ^//us edulis, Chthamalus dalli, Balanus
glandula, and B. cariosus—weve chosen for study
because they are widespread in Alaska; and where
they occur, they usually occupy greater proportions
of rocky intertidal space than other sessile inverte-
brates. Not one of these species was present in plots
in the upper intertidal zone at the Pribilof Islands
(Fig. 64-7). However, small M. edulis were collected
in three of four plots above mean high water at St.
George Island and in two of seven plots above mean
high water at Otter Island (above the upper tidal level
considered in this study). M. edulis was present in
lower intertidal plots at both St. George and Otter
islands but was represented only by small individuals
(<15 mm in length) whose biomass varied greatly
between plots (Fig. 64-7).
B. glandula was represented by a single individual
in one plot in the lower intertidal zone at Otter
Island. B. cariosus was absent from plots in both
intertidal zones in the Pribilof Islands but present in 2
of 27 plots below mean low water at St. George
Island. Unidentified barnacles (Balanus sp.) were
collected in 3 of the 27 plots.
Barnacles tended to be more abundant at Amak
1122 Benth ic b iology
TABLE 64-9
Food of Littorina spp.^
North Pacific
species
North Atlantic species
Littorina
Littorina
Littorina
Littorina
Food
scutulata
planaxis
Food
littorea
saxatilis
Bacillariophyceae
Bacillariophyceae
diatoms
2,5,7
5,7
diatoms
3,8^
1^
Cyanophyceae
Chlorophyceae
unicellular blue-green algae
5,7
5,7
Ulothrix-Urospora
9^
Dermocarpa
5
5
Monostroma
8,9
Spirulina
5
5
Enteromorpha
3,9
Calothrix
5
5
Ulva
3,9
Plectonema
5
5
Spongomorpha
Cladophora
Pseudoendoclonium
9
8,9
1
Chlorophyceae
Prasiola
4b
Phaeophyceae
Ulva
4
Ectocarpus-Pylaiella
8,9
Spongomorpha
5
5
Elachistea
9
Cladophora
4
4
Ascophyllum
6,8,9
Phaeophyceae
Fucus
6,8.9
Laminaria
4
Pelvetia
6
Pelvetia
4
Petalonia
Scytosiphon
9
9
Rhodophyceae
Rhodophyceae
Porphyra
4
4c
Porphyra
9
Rhodochorton
5
5
Rhodymenia
8,9
Rhodoglossum
4c
Ceramium
9
Endocladia
5
4S5
Halosaccion
9
^Numbers in body of table refer to the following papers: 1, Berry (1961); 2, Castenholz (1961); 3, Newell (1958); 4, Dahl
(1964); 5, Foster (1964); 6, Bakker (1959); 7, Glynn (1965); 8, Hayes (1929); 9, Lubchenco (1978).
^ Small plants eaten.
•^ Finely chopped but not whole plants eaten.
'^Diatoms in gut did not appear to be digested.
^ All genera from Lubchenco's list of highly preferred food are included here. Not all genera of medium and low preference
ranking are included. See Table 1 of Lubchenco (1978) for complete list.
and Akun islands than at Otter and St. George islands
(Fig. 64-7). B. glandula was absent from upper and
lower intertidal zones at Akun and Amak islands,
respectively, but present above (in 2 of 2 plots) and
below (in 1 of 11 plots) the respective upper and
lower limits of this study at these two sites.
M. edulis appears to be an exception to the trend
toward greater abundance among major sessile
animals with decreasing frequency of ice scouring.
Although three large (>20 mm) M. edulis were
present in one plot below mean low water at Akun
Island, only eight small individuals were found
in one of five plots in the upper intertidal zone at
Akun Island. None were found in the other four
plots. M. edulis was absent from all plots sampled at
Amak Island. From these data, I was unable to
account for the apparently small populations of M.
edulis at Amak and Akun islands.
REFUGES FROM ICE SCOURING
The quantitative sampling used in this study
emphasized upper rock surfaces at all sites; the effects
of scouring by ice are most pronounced on these
surfaces (Fig. 64-8). Cracks, kettles, and other
habitats protected from ice scouring frequently
contain a well-developed biota (Madsen 1936, Vibe
1950, Ellis and Wilce 1961). In the present study,
species richness of marine organisms on upper rock
surfaces scoured by ice was low. However, observa-
tions and photographs of the biota in rock crevices
and between and beneath closely packed boulders at
the Pribilof Islands indicate that species richness in
these places is comparable to species richness of
unscoured surfaces at Amak and Akun islands (T. R.
Merrell, Jr., personal communication, 1979). Such
\
i
Intertidal scouring by sea ice 1 123
.«-N
1,000
>.^
\-
100
I
O
10
LU
^
1.0
1-
LU
0.1
^
0
SESSILE INVERTEBRATES
UPPER INTERTIDAL
2
3 1
_L
_L
4
1 - Balanus cariosus
2 " Balanus gland ula
3" Chthamalus dalli
4 - Mytilus edulis
I-
I
g
UJ
LU
ST. GEORGE
ISLAND
OTTER
ISLAND
AMAK
ISLAND
AKUN
ISLAND
Figure 64-7. Mean weight of sessile invertebrates at two ice-scoured (St. George and Otter islands) and two unscoured
islands in the Bering Sea. Vertical lines are 95-percent confidence intervals.
places apparently are refugia for species whose
growth form or light requirements, or both, permit
them to occupy such micro habitats. In one area of
shore at Garden Cove, St. George Island, deep fissures
in the bedrock and offshore reefs protected much of
the rock surface from ice scouring (T. R. Merrell, Jr.,
personal communication, 1979). The biota included
large Collisella pelta, urchins, and several species of
sessile organisms, including Balanus cariosus, two
sponges, hydroids, bryozoans, tubeworms, tunicates,
and coralline algae (R. T. Myren, unpublished data on
file at Northwest and Alaska Fisheries Center, Auke
Bay Laboratory, Juneau).
Subtidal observations by divers from the Auke Bay
Laboratory indicated that the effect of ice scour
generally reached 3-4 m in depth. In June 1976,
six weeks after the last ice-scouring episode, N. Calvin
(personal communication 1979) and others observed
that above this lower limit at several locations, the
upper surfaces of rock were occupied primarily by
filamentous green algae and small individuals of
Alaria sp. These algae had probably settled and
Figure 64-8. Intertidal region at English Bay, St. Paul
Island. Note lack of biological cover on tops of boulders.
10 June 1976.
1124 Benthic biology
TABLE 64-10
Tests of significance ot Littorina wet weights (L. sitkana andL. aleutica combined) in the rocky intertidal region at the
Pribilof Islands compared with Amak and Akun islands. ** = 0.001 < p < 0.01.
Source
d.f.
Anova
SS
MS
Site
Error
Total
3
44
47
143.8
393.5
537.4
47.9
8.9
5.36**
Treatment
n
Mean of trans-
formed counts*
95%Confidence interval
Lower limit Upper limit
St. George Island (G)
Otter Island (O)
Amak Island (Am)
Akun Island (Ak)
6
21
8
13
5.27
6.24
1.31
5.43
2.81
4.93
-0.82
3.75
7.73
7.56
3.44
7.1
Comparison
K
Significance
G-0 vs Am-Ak
G-0 vs Am
G-0 vs Ak
5.94
i.94
6.14
44
44
P<0.05'^
P<0.05'=
ns"^
^Weights were scaled (X 1000) before transformation (log [x + 1]) to avoid negative characteristics.
^A priori orthogonal comparison.
'^A posteriori comparison with Scheffe's test (Scheffe 1953). S, K, and n^ are statistics of Scheffe's test. S^ = the experiment-
wise error, K = number of cell means, n^, = degrees of freedom of the error term of the anova, ns = not significant.
grown there since the last scouring episode.
Green sea urchins (Strongylocentrotus sp.) had
apparently just begun grazing the algae in June.
Larger plants, presumably survivors of one or more
winters, were found only in crevices and between
large rocks. The fronds (and stipes in some cases)
of Laminaria longipes were often sharply cropped at
the level of the rock surface. Large perennial plants
such as Alaria sp., Laminaria dentigera, and Thalas-
siophyllum sp. flourished below 4 m. Several-year-
old Constantinea plants were observed at 5 m. Below
the depth influenced by sea ice, the sublittoral region
appeared exceptionally rich in species compared to
the benthos at shallower depths.
In the Pribilof Islands, greater species richness
among invertebrates and algae in intertidal refugia
and below the lower limit of scouring by sea ice in
the sublittoral region suggests that the effects of
island biogeography and regimes of temperature and
salinity are negligible compared to the effect of ice
scouring.
DISCUSSION
Scouring by sea ice is probably the most important
disturbance affecting intertidal community structure
at the Pribilof Islands. My results indicate that
species diversity is low where the frequency of
scouring is high and that ice scouring probably causes
the low species diversity. However, Huston (1979)
contends that the frequency of disturbance alone
cannot adequately predict species diversity and that
Interlidal scouring by sea ice 1 125
diversity represents a dynamic equilibrium between
the rate of population reduction by disturbance or
predation and the rate of approach to competitive
equilibrium. Thus, to fully evaluate the effect of sea
ice on an intertidal community, we need to know the
rates of growth of the populations of potential
competitors.
Information on the rate of population reduction
and the rate of competitive displacement is important
to the study of the effect of oil pollution on an
intertidal community because an oil spill could (1)
increase density-independent mortality in many
species and (2) limit the population growiih rates of
surviving competitors by suppressing primary produc-
tion, interfering with feeding behavior, or reducing
fecundity or setting success. These two main effects
could offset each other if the rate of competitive
displacement and the frequency of population
reduction were not markedly disparate (i.e., if one
were not of overriding importance), and the oil spill
were mild. However, because of the high rate of
disturbance by sea ice in ice-stressed systems, the
community might be far enough from competitive
equilibrium that species diversity would be further
reduced.
The most important characteristic of ice-stressed
coasts allowing species to remain in the system is the
availability of refuges from ice scouring. Woodin
(1978) suggests five major categories of refuges from
disturbance: temporal periods (1) outside or (2)
within the activity range of the disturbance process,
(3) spatial zones beyond or (4) physical hetero-
geneities within the activity range of the distur-
bance process, and (5) biologically generated refuges
within the activity range of the disturbance process.
Because it is unlikely that biogenic structures could
withstand ice scour, category 5 is probably unimpor-
tant in ice-stressed systems. Some motile species
could migrate onto scoured surfaces during a scouring
episode, for example, after ice was temporarily lifted
from lower intertidal surfaces at high tide (category
2), but there seems to be little advantage in this
because the animal must return to a refuge within 12
hours at most, and recently scoured rock would
probably have little to attract it.
Spatial zones beyond the range of scouring (e.g.,
supralittoral or sublittoral habitats) could be impor-
tant for some species. However, because the supra-
littoral zone is above the upper physiological limits of
most intertidal species and because predators and
competitors often prevent them from establishing
populations in the sublittoral region (Connell 1972),
few intertidal species could successfully occupy these
habitats.
Temporal periods outside the range of ice scouring
(i.e., June through December) and physical hetero-
geneities (interstices of boulder fields and crevices)
during ice scouring remain the primary refuges
available to intertidal organisms at the Pribilof
Islands. Refuges provided by physical heterogeneities
probably are more important than temporal refuges,
because for a species to use the temporal refuge it
would have to have a planktonic stage (e.g., spores,
gametes, or larvae) that could weather the scouring
episode; it would thereby risk having its propagules
swept away from the islands. Refuges provided by
spatial heterogeneities, on the other hand, can harbor
many life stages— minute sporophytes, microscopic
gametophytes, and sometimes macroscopic algae and
egg masses, juveniles, and adults of many inverte-
brates.
None of the refuges from ice scouring could offer
complete protection from an oil spill. Depending on
wind and wave action, both supralittoral and sublit-
toral habitats might be contaminated. An oil spill
reaching the shores of the Pribilof Islands in the
months from June through December would immed-
iately interrupt the progress of ecological succession.
An offshore oil spill might be temporarily prevented
from coming ashore when the Pribilof Islands are iced
in; but, depending on wind and currents, oil could
reach the shore as the ice gradually recedes north. Oil
in contact with ice weathers very slowly (Atlas et al.
1978). The toxicity of the oil would probably still
be great, and the physical characteristics of oil that
interfere with feeding and respiration would probably
not be irreversibly altered by the time oil eventually
reached the shore. Oil reaching the shore when ice is
present could be abraded, redistributed, and dispersed
somewhat by ice scouring. But sea ice also prevents
wave generation and dampens existing waves, thereby
reducing mechanical dispersal, possibly the most
important mechanism for dispersion at higher lati-
tudes (Owens 1978).
Physical heterogeneities on rocky shores in the
Pribilof Islands are coarse grained (compared with
gravelly, sandy, or muddy beaches), and interstitial
spaces are Izirge— even heavy oils can penetrate them.
Moreover, rates of abrasion and dispersion are re-
duced in coarse-grained substrates (Owens 1978).
The primary refuge from ice scour for intertidal
organisms would become rapidly contaminated for a
prolonged period if oil washed ashore at the Pribilof
Islands. The net effect of an oil spill probably would
be a proportionately large reduction in species
richness, perhaps involving local extinction of some
species and a prolonged period of return to a natural
community.
1126 Benthic biology
ACKNOWLEDGMENTS
The data used in this study were collected under
the supervision of S. Zimmerman and T. Merrell. L.
Barr, N. Calvin, R. Ellis, J. Gharrett, J. Hanson, J.
MacKinnon, and R. Myren participated in the field
work. I have relied heavily on the personal observa-
tions of these people as well as on those of T. Merrell
to augment the evidence of the quantitative samples,
and I am grateful for their contribution. I thank N.
Calvin, J. Fujioka, E. Haynes, L. Barr, and T. Merrell
for critically reading the manuscript; D. V. Ellis
alerted me to the papers of Madsen and Vibe and
offered several helpful suggestions. I am pleased to
acknowledge the editorial assistance of E. Fritts, who
patiently read several drafts of the manuscript.
This work was sponsored in part by the Outer
Continental Shelf Environmental Assessment Program
(OCSEAP).
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1965
Behrens, S.
1971
Berry, A. J.
1961
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Briggs, J. C.
1974
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The distribution and abundance of the
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F. Chia, and R. R. Strathmann
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delay of metamorphosis and growth
in the seastar, Mediaster aequalis
Stimpson. Biol. Bull. 141:99-108.
Marine zoogeography.
N.Y.
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i
Epifaunal Invertebrates of the Continental Shelf
of the Eastern Bering and Chukchi Seas
Stephen C. Jewett and Howard M. Feder
Institute of Marine Science
University of Alaska
Fairbanks
ABSTRACT
Epifaunal invertebrates were surveyed over much of the
eastern Bering and Chukchi seas continental shelf. Informa-
tion on the distribution, abundance, and biomass of the
dominant species is discussed by area and depth strata. Four
commercially important crabs (Paralithodes camtschatica,
P. platypus, Chionoecetes opilio, and C. bairdi) and four
sea-star species {Asterias amurensis, Euasterias echinosoma,
Leptasterias polaris acervata, and Lethasterias nanimensis)
account for nearly 70 percent of the epifaunal biomass of the
entire eastern shelf region. Commercially important crabs
dominate the southeastern portion of the shelf; echino-
derms, in particular sea stars, abound in the northeastern
Bering Sea and southeastern Chukchi Sea.
INTRODUCTION
The eastern Bering Sea shelf is one of the greatest
producers of commercial shellfish and fish in the
world. In 1979, multinational catches of groundfish
and snow (Tanner) crab approximated 2 X 10^ mt
and 50.1 X 10^ mt, respectively (J. Reeves, Nat. Mar.
Fish. Serv., personal communication, 1980). Domes-
tic catches of king crab have continued to rise annu-
ally; the 1979-80 fishing season yielded 53.3 X 10^
mt. Although clams are not currently harvested,
recent assessments of the clam resource indicate that
a resource of harvestable-size surf clams amounting to
from 277 X 10^ to 381 X 10^ mt occurs over an area
of 5,180 km^ in the southeastern Bering Sea (Hughes
and Nelson 1979; Hughes and Bourne, Chapter 67,
this volume). Interest also exists in exploitation and
development of the shelf for its petroleum resources.
Fishing and oil development may bring about major
changes to the resident biota. In order to better
anticipate and evaluate possible damage to the Bering
Sea ecosystem, information must be available con-
cerning species composition, distribution, abundance,
biomass, and life histories of the fauna there.
Results of a variety of biological investigations of
the pelagic and benthic environments in the eastern
Bering and Chukchi seas are presented in this book.
Infaunal studies have also been carried out in the
eastern Bering and Chukchi seas (e.g., Neiman 1963;
Semenov 1964; Feder and Mueller 1974; Haflinger
1978; Stoker 1978; and Hughes and Nelson 1979;
also see Stoker, Chapter 62; Haflinger, Chapter 63;
McDonald et al., Chapter 66; Hughes and Bourne,
Chapter 67; Macintosh and Somerton, Chapter 68).
Epifaunal invertebrates of the eastern Bering Sea
were first examined during the trawling operations of
the Harriman Alaska Expedition in 1899 (Merriam
1904). Additional, but limited, information on
epifauna is found in the reports of the pre-World-
War-II king crab investigations (Fishery Market
News 1942) and in the reports on fishing and process-
ing operations of the Pacific Explorer in 1948
(Wigutoff and Carlson 1950). Some information on
species found in the northern Bering Sea is included
in reports of the U. S. Fish and Wildlife Service
(Ellson et al. 1949, 1950). A research program of
the Bureau of Commercial Fisheries Commission
during the summers of 1958 and 1959 included an
ecological study of the eastern Bering Sea with
emphasis on epifaunal invertebrates (McLaughlin
1131
1132 Benth ic h io logy
1963). Sparks and Pereyra (1966) present a partial
checklist and general discussion of the benthic fauna
of the southeastern Chukchi Sea for the summer of
1959. Feder and Mueller (1974) include species lists,
population density, and biomass of benthic epifauna
collected in a survey of the northeastern Bering Sea
near Nome. Neiman (1963) and Alton (1974)
discuss the proportion of benthos available as food
to bottom-feeding species in various regions of the
Bering Sea. Shellfish resources of the shelf of the
eastern Bering and Chukchi seas are presented by
Pereyra et al. (1976) and Wolotira et al. (1977).
The OCSEAP data of Feder and Jewett (1978,
1980; on file at National Oceanographic Data Center)
on the distribution, abundance, and biomass of the
dominant epibenthic species from the southeastern
and northeastern Bering Sea and southeastern
Chukchi Sea serve as the basis for this chapter.
METHODS
Epifaunal invertebrates were collected during a
cruise of the NO A A ship Miller Freeman. Sampling
was conducted in selected study areas in the south-
eastern Bering Sea from August to October 1975 and
April to June 1976 and in the northeastern Bering
Sea and southeastern Chukchi Sea in September and
October 1976. The northeastern Bering Sea between
60° 30' latitude and 63° 00' latitude was not sampled.
Half-hour and one-hour tows were made at predeter-
mined stations with a 400-mesh Eastern otter trawl.
All invertebrates were sorted aboard ship, given
tentative identifications, counted, weighed, and
aliquot samples of each species preserved for final
identification at the Institute of Marine Science,
University of Alaska.
SOUTHEASTERN BERING SEA
In trawling operations in the southeastern Bering
Sea in 1975 and 1976, epifaunal invertebrates were
collected from 254 stations (Feder and Jewett
1980): 36 stations at depths from 0-40 m, 148
stations at > 40-1 00 m, and 70 stations at >100m
(Fig. 65-1).
180°
175^
170°
165°
160'
155°
TRAWL STATION LOCATIONS
S.E. Bering Sea
175"
170°
165°
160°
Figure 65-1. Benthic trawl stations occupied in the southeastern Bering Sea, 1975-76.
Epifaunal invertebrates 1133
The average epifaunal biomass at all depths was
4.1 g/m^ . The biomass average was highest at the
> 40-100 m depth stratum (4.8 g/m^ ) and lowest at 0-
40 m (1.9 g/m') (Fig. 65-2).
Invertebrates collected included 11 phyla, at least
110 families, and 235 species. MoUusks dominated
the species list with 100 (42.6 percent) of the species,
while arthropods and echinoderms contributed 28.5
percent and 16.6 percent of the species, respectively
(Tables 65-1, 65-2, and 65-3).
Among the 11 phyla collected, Arthropoda and
Echinodermata dominated the biomass. Thirteen
species, each contributing at least 1 percent of the
biomass, made up more than 80 percent of the total
epifaunal biomass. Arthropods comprised more than
59 percent of the total.
The 0-40 m depth stratum was dominated by
echinoderms, particularly the sea star Asterias
amurensis, with an average biomass of 1.6 g/m^ or
84.4 percent of the total stratum biomass. This
species became less important as depth increased; it
constituted only 12.7 percent of the biomass at
>40-100 m and 0.4 percent at >100 m. The species
contributing most to the biomass at > 40-100 m were
the snow crabs Chionoecetes opilio and C. bairdi, with
22.2 percent and 5.3 percent of the total epifaunal
biomass, respectively, and the king crabs Paralithodes
camtschatica and P. platypus, with 19.1 percent and
2.4 percent of the total, respectively. Stations deeper
than 100 m were dominated by C. opilio, C. bairdi,
and P. camtschatica. These three crab species made
up 73.9 percent of the biomass at deep-water sta-
tions.
NORTHEASTERN BERING SEA
Sampling in the northeastern part of the Bering
Sea in 1976 produced collections at 106 stations
(Feder and Jewett 1978). Ninety-nine of these
stations were from the 0-40 m depth stratum and
seven were from >40-100 m (Fig. 65-3).
The mean epifaunal biomass for all stations was
3.1 g/m^ . The biomass was highest at >40-100 m
(4.2 g/m^ ). Biomass at stations from 0-40 m was
3.0 g/m^ (Fig. 65-4).
180"
175'
170°
165°
160°
155'
TOTAL EPIFAUNAL BIOMASS
S.E. Bering Sea
Biomass (g/m^
° < 3
3< O <6
6< CD <9
9< CD
175"
170
165'
160'
Figure 65-2. Distribution and biomass of total epifauna in thie southeastern Bering Sea.
1134 Benthic b io logy
TABLE 65-1
Number and percentage of epifaunal species by phylum and depth in the Bering Sea and Chukchi Sea
0-40 m
Southeastern
>40-100 m
Bering Sea
>100 m=
All depths
SPECIES
Phylum
Number
Percent
Number
Percent
Number
Percent
Number
Perceni
Porifera
1
1.1
1
0.6
1
0.7
1
0.4
Cnidaria
4
4.5
4
2.4
6
3.9
7
3.0
Annelida
5
5.6
8
4.7
7
4.6
10
4.3
MoUusca
36
40.4
80
47.3
59
38.6
100
42.6
Arthropoda
28
31.5
49
28.8
41
26.8
67
28.5
Sipuncula
0
0
1
0.6
0
0
1
0.4
Echiura
1
1.1
1
0.6
1
0.7
1
0.4
Ectoprocta
1
1.1
1
0.6
0
0
1
0.4
Brachiopoda
0
0
0
0
3
2.0
3
1.3
Echinodermata
11
12.4
20
11.8
34
22.2
39
16.6
Urochordata
2
2.2
5
3.0
1
0.7
5
2.1
Totals
89
100.0
170
100.0
153
100.0
235
100.0
Northeastern Bering Sea
Porifera
3
1.5
2
2.4
3
1.4
Cnidaria
9
4.5
4
4.8
9
4.3
Rhynchocoela
0
0
1
1.2
1
0.5
Annelida
15
7.5
5
6.0
15
7.1
MoUusca
73
36.3
22
26.2
76
36.0
Arthropoda
48
23.9
22
26.2
52
24.6
Sipuncula
1
0.5
0
0
1
0.5
Echiura
1
0.5
1
1.2
1
0.5
Priapulida
1
0.5
0
0
1
0.5
Ectoprocta
9
4.5
5
6.0
10
4.7
Brachiopoda
1
0.5
1
1.2
2
0.9
Echinodermata
28
13.9
13
15.5
28
13.3
Urochordata
12
6.0
8
9.5
12
5.7
Totals
201
100.0
84
100.0
211
100.0
Southeastern Chukchi Sea
Porifera
4
2.6
3
2.4
5
2.7
Cnidaria
8
5.3
6
4.7
8
4.3
Rhynchocoela
0
0
1
0.8
1
0.5
Annelida
8
5.3
11
8.7
16
8.6
MoUusca
58
38.4
48
37.8
71
38.2
Arthropoda
32
21.2
24
18.9
39
21.0
Sipuncula
1
0.7
1
0.8
1
0.5
Echiura
1
0.7
1
0.8
1
0.5
Ectoprocta
9
6.0
4
3.1
9
4.8
Echinodermata
21
13.9
20
15.7
25
13.4
Urochordata
9
6.0
8
6.3
10
5.4
Totals
151
100.0
127
100.0
186
100.0
^Stations were not sampled at depths greater than 100 m in the northeastern Bering Sea and southeastern Chukchi Sea.
The material collected included 13 phyla, at least
101 families, and 211 species. Three phyla contrib-
uted 73 percent of the species taken from this region.
MoUusks dominated the species list with 76 species,
followed by Arthropoda with 52 species and Echino-
dermata with 28 species (Tables 65-1, 65-2, and
65-3).
Echinoderms accounted for over 80 percent of the
total biomass. Arthropods and moUusks were next in
importance with 8.4 percent and 5.1 percent of
the total biomass, respectively. Of 11 species, each
comprising more than 1 percent of the biomass, 5
were species of sea stars {Asterias amurensis, A.
rathbuni, Euasterias echinosoma, Leptasterias polaris
acervata, and Lethasterias nanimensis), one was the
basket star Gorgonocephalus caryi, and another the
sea urchin Strongylocentrotus droebachiensis.
The king crab Paralithodes camtschatica was the
most important component of the arthropod biomass
and the whelk Neptunea heros was the leading
molluscan species in biomass.
Epifaunal invertebrates 1135
TABLE 65-2
Biomass^ (Bio.) of the epifaunal phyla by depth in the Bering Sea and Chukchi Sea
Southeastern Bering Sea
0-40 m
>40-100
m
>100
m"
All depths
Phylum
xg/m^
%Tot. Bio.
xg/m^
% Tot. Bio.
xg/m^
% Tot. Bio.
xg/m^
% Tot. Bio
Fori f era
0.013
0.68
0.286
5.94
0.053
1.34
0.183
4.41
Cnidaria
0.031
1.68
0.244
5.07
0.151
3.81
0.188
4.55
Annelida
<0.001
<0.01
<0.001
0.02
<0.001
0.01
<0.001
0.01
Mollusca
0.039
2.09
0.307
6.38
0.155
3.92
0.227
5.47
Arthropoda
0.125
6.73
2.662
55.23
3.239
81.97
2.460
59.39
Sipuncula
0
0
<0.001
<0.01
0
0
<0.001
<0.01
Echiura
<0.001
<0.01
<0.001
<0.01
<0.001
<0.01
<0.001
<0.01
Ectoprocta
<0.001
0.03
<0.001
0.01
0
0
<0.001
0.01
Brachiopoda
0
0
0
0
<0.001
<0.01
<0.001
<0.01
Echinodermata
1.603
86.05
0.811
16.83
0.351
8.89
0.781
18.85
Urochordata
0.051
2.73
0.507
10.53
0.002
0.04
0.302
7.30
Totals
1.863
100.0
4.819
100.0
3.952
100.0
4.142
100.0
Northeastern Bering Sea
Porifera
0.001
0.03
0.217
5.15
0.014
0.44
Cnidaria
0.111
3.67
0.076
1.80
0.109
3.52
Rhynchocoela
0
0
<0.001
<0.01
<0.001
<0.01
Annelida
0.001
0.03
<0.001
<0.01
<0.001
0.03
Mollusca
0.163
5.39
0.044
1.06
0.156
5.05
Arthropoda
0.260
8.60
0.274
6.49
0.261
8.43
Sipuncula
<0.001
<0.01
0
0
<0.001
<0.01
Echiura
<0.001
<0.01
0
0
<0.001
<0.01
Priapulida
<0.001
<0.01
0
0
<0.001
<0.01
Ectoprocta
0.002
0.06
0.006
0.14
0.002
0.69
Brachiopoda
<0.001
<0.01
<0.001
<0.01
<0.001
<0.01
Echinodermata
2.426
80.26
3.571
84.61
2.493
80.60
Urochordata
0.058
1.94
0.031
0.73
0.057
1.84
Totals
3.023
100.0
4.221
100.0
3.093
100.0
Southeastern Chukchi Sea
Porifera
<0.001
0.16
0.089
1.93
Cnidaria
0.173
6.21
0.072
1.55
Rhynchocoela
0
0
<0.001
<0.01
Annelida
<0.001
0.02
0.016
0.34
Mollusca
0.457
16.40
0.352
7.58
Arthropoda
0.433
15.56
0.345
7.42
Sipuncula
<0.001
<0.01
<0.001
<0.01
Echiura
<0.001
<0.01
<0.001
<0.01
Ectoprocta
0.005
0.18
0.001
0.02
Echinodermata
1.609
57.74
2.893
62.18
Urochordata
0.107
3.85
0.881
18.93
Totals
2.787
100.0
4.652
100.0
0.025
0.77
0.145
4.37
<0.001
<0.01
0.005
0.15
0.430
12.91
0.408
12.34
<0.001
<0.01
<0.001
<0.01
0.004
0.12
1.971
59.49
0.325
9.82
3.314
100.0
"Based on all stations examined.
''Stations were not sampled at depths greater than 100 m in the northeastern Bering Sea and southeastern Chukchi Sea.
The shallow stations (0-40 m) were dominated by
the sea star Asterias amurensis, which comprised 56.3
percent of the biomass and averaged 1.7 g/m^ .
This sea star was of minor importance in deeper water
(>40-100 m), making up only 1.5 percent of biomass
in the stratum and averaging <0.1 g/m^ . Although
two other echinoderms (S. droebachiensis and G.
caryi) were of only minor importance at 0-40 m (6.6
percent of the biomass), they dominated the deeper
stations, where they comprised over 78.5 percent of
the biomass.
SOUTHEASTERN CHUKCHI SEA
In benthic trawling in the southeastern Chukchi
Sea in 1976 epifaunal invertebrates were collected
from 69 stations (Feder and Jewett 1978); 48 sta-
tions were from 0 to 40 m and 21 stations were
from >40 to 100 m (Fig. 65-5).
The mean epifaunal biomass at all depths was
3.3 g/m^ . The mean biomass was higher in the
>40-100 m depth stratum (4.6 g/m^ ) and lower at
0-40 m (2.8 g/m' ) (Fig. 65-6).
TABLE 65-3
Biomass^ (Bio.) of some dominant epifaunal species by depth in the Bering Sea and Chukchi Sea
Soutlieastem Bering Sea
0-40
m
>40-100
m
>100
m"
All depths
Species
xg/m^
% Tot. Bio.
xg/m^
% Tot. Bio.
xg/m^
% Tot. Bio.
xg/m^
% Tot. Bio.
Neptunea ventricosa
0.017
0.93
0.063
1.31
0.013
0.34
0.042
1.03
N. hems
0.014
0.78
0.118
2.45
<0.001
<0.01
0.070
1.71
Pagurus trigonocheirus
<0.001
0.01
0.075
1.56
0.009
0.24
0.046
1.12
Paralithodes camtschatica
0.022
1.19
0.919
19.07
0.669
16.94
0.722
17.44
P. platypus
0
0
0.118
2.45
0.039
0.99
0.079
1.92
Hyas coarctatus alutaceus
0.006
0.32
0.028
0.59
<0.001
<0.01
0.017
0.42
Chionoecetes (hybrid)
0
0
0.072
1.51
0.192
4.85
0.095
2.30
C. opilio
<0.001
0.02
1.071
22.23
1.252
31.67
0.968
23.38
C. bairdi
0.002
0.09
0.256
5.31
1.000
25.31
0.426
10.27
Erimacrus isenbeckii
0.003
0.15
0.073
1.51
0.015
0.38
0.047
1.13
Asterias amurensis
1.572
84.42
0.611
12.69
0.017
0.44
0.584
14.10
Evasterias echinosoma
0
0
0.006
0.12
0
0
0.003
0.08
Leptasterias polaris acervata
<0.001
0.01
0.062
1.29
<0.001
0.02
0.036
0.88
Lethasterias nanimensis
<0.001
0.01
0.012
0.26
0.003
0.07
0.008
0.19
Strongylocentrotus droebachiensis
0.002
0.14
<0.001
0.01
0.003
0.07
0.001
0.03
Gorgonocephalus caryi
0
0
0.080
1.66
0.284
7.18
0.108
2.63
Styela rustica macrenteron
0.040
2.16
0.350
7.26
0
0
0.209
5.05
Halocynthia aurantium
0
0
0.112
2.34
0
0
0.065
1.58
Totals
1.678
90.22
4.026
83.62
3.496
88.50
3.526
85.26
Northeastern Bering Sea
Neptunea ventricosa
0.018
0.60
0.013
0.32
N. hews
0.116
3.84
0.017
0.40
Pagurus trigoncheirus
0.034
1.14
0.019
0.45
Paralithodes camtschatica
0.076
2.52
0
0
P. platypus
0.004
0.14
0.077
1.84
Hyas coarctatus alutaceus
0.035
1.18
0.066
1.57
Chionoecetes opilio
0.007
0.24
0.075
1.77
Asterias amurensis
1.701
56.27
0.064
1.54
A. rathbuni
0.048
1.61
0
0
Evasterias echinosoma
0.131
4.34
0.046
1.10
Leptasterias polaris acervata
0.129
4.28
0.071
1.69
Lethasterias nanimensis
0.192
6.36
0.011
0.25
Strongylocentrotus droebachiensis
0.071
2.37
0.945
22.39
Gorgonocephalus caryi
0.127
4.21
2.368
56.12
Chelyosoma spp.
<0.001
0.02
<0.001
<0.01
Styela rustica macrenteron
0.027
0.91
0.001
0.02
Halocynthia aurantium
0.001
0.05
0.013
0.31
Totals
2.717
90.09
3.785
89.77
0.037
1.21
Southeastern Chukchi Sea
Neptunea ventricosa
0.049
1.78
0.038
0.82
N. heros
0.373
13.39
0.262
5.64
Pagurus trigonocheirus
0.067
2.40
0.060
1.29
Paralithodes camtschatica
<0.001
0.03
0
0
P. platypus
<0.001
0.02
0.004
0.08
Hyas coarctatus alutaceus
0.036
1.30
0.097
2.08
Chionoecetes opilio
0.203
7.29
0.110
2.38
Asterias amurensis
0.889
31.91
0.176
3.80
A. rathbuni
0.094
3.40
0.048
1.04
Evasterias echinosoma
0.096
3.45
0.191
4.10"=
Leptasterias polaris acercata
0.151
5.42
1.105
23.76
Lethasterias nanimensis
0.197
7.08
0.160
3.44
Strongylocentrotus droebachiensis
0.023
0.83
0.704
15.14
Gorgonocephalus caryi
0.020
0.74
0.358
7.70
Chelyosoma spp.
0.048
1.76
0.420
9.03
Styela rustica macrenteron
0.033
1.21
0.160
3.45
Halocynthia aurantium
<0.001
0.01
0.192
4.14
Totals
2.281
82.02
4.085
87.89
0.018
0.59
0.110
3.56
0.033
1.09
0.071
2.32
0.008
0.27
0.011
0.37
1.605
51.89
0.046
1.48
0.126
4.08
0.126
4.07
0.182
5.88
0.123
3.97
0.258
8.36
<0.001
0.02
0.025
0.84
0.002
0.07
2.781
90.07
0.046
1.40
0.342
10.33
0.065
1.96
:o.ooi
0.02
0.001
0.05
0.053
1.61
0.177
5.35
0.689
20.79
0.082
2.47
0.123
3.71
0.420
12.67
0.187
5.64
0.215
6.49
0.116
3.49
0.153
4.63
0.069
2.09
0.054
1.64
2.792
84.34
^Based on all stations examined.
''Stations were not sampled at depths greater than 100 m in the northeastern Bering Sea and southeastern Chukchi Sea.
<^ Based mainly on one station at 42 m.
1136
Epifaunal invertebrates 1137
175* 173* 171
Figure 65-3. Benthic trawl stations occupied in tiie north-
eastern Bering Sea, 1976.
I TOTAL EPIFAUNAL BIOMASS
Norton Sound
I Biommi l9/m' >
4 ^ O < 8
8< O <'J
12* Q
173° 17
Figure 65-4. Distribution and biomass of total epifauna
in the northeastern Bering Sea.
Invertebrates included 11 phyla, 94 families, and
186 species. The phyla containing the majority of
the species were MoUusca (71 species), Arthropoda
(39), Echinodermata (25), and Annelida (16);
Urochordata (Chordata), Ectoprocta, and Cnidaria
had 10, 9, and 8 species, respectively (Tables 65-1,
65-2, and 65-3).
Echinodermata were dominant in biomass (59.5
percent). Mollusca, Arthropoda, and Urochordata
contributed 12.9, 12.3, and 9.8 percent of the total
biomass, respectively.
Fifteen species made up 84.3 percent of the
epifaunal biomass. The most important species were
the echinoderms Asterias amurensis (20.8 percent of
the total biomass) and Leptasterias polaris aceruata
(12.7 percent) and the moWusk Neptunea heros (10.3
percent).
The 0-40 m depth stratum was dominated by
Asterias amurensis and Neptunea heros; deeper
stations, > 40-1 00 m, had higher concentrations of
Leptasterias polaris acervata and Strongylocentrotus
droebachiensis.
DOMINANT EPIFAUNAL SPECIES
The following 11 species were dominant in biomass
or abundance, or both, in at least one of the three
study areas.
Whelk Neptunea heros
Among the more than 100 species of moUusks
encountered, Neptunea heros was the dominant
species in all three study areas (Tables 65-3 and 65-4;
Figs. 65-7 to 65-9). The biomass of this whelk
increased with increasing latitude; it was most evident
in the southeastern Chukchi Sea, where it made up
10.3 percent of the total epifaunal biomass with an
average biomass of 0.3 g/m^ . Neptunea heros had a
mean density of 44.1 indiv./km in the southeastern
Figure 65-5. Benthic trawl stations occupied in the south-
eastern Chukchi Sea, 1976.
Figure 65-6. Distribution and biomass of total epifauna
in the southeastern Chukchi Sea.
TABLE 65-4
Average density^ (indiv./km) of some dominant epifaunal species by depth in the Bering Sea and Chukchi Sea
Species
0-40 m
Southeastern Bering Sea
>40-100 m >100 m^
All depths
Neptunea ventricosa
N. hews
Pagurus trigonocheirus
Paralithodes camtschatica
P. platypus
Hyas coarctatus alutaceus
Chionoecetes (hybrid)
C. opilio
C. bairdi
Erimacrus isenbeckii
Asterias amurensis
Evasterias echinosoma
Leptasterias polaris acervata
Lethasterias nanimensis
Strongylocentrotus droebachiensis
Gorgonocephalus caryi
Styela rustica macrenteron
Halocynthia aurantium
Totals
1.99
1.05
0.08
0.29
2.05
0.20
0.08
0.06
157.64
0.01
0.01
0.50
10.16
174.12
4.24
8.84
54.90
11.32
0.89
3.39
6.10
173.11
13.64
0.68
51.09
0.05
2.65
0.31
0.06
3.91
43.61
0.69
379.48
0.72
0.01
3.66
5.69
0.29
0.01
6.14
126.66
26.10
0.33
1.02
0.03
0.08
0.52
15.61
186.87
2.94
5.29
32.92
8.19
0.60
2.27
5.24
135.64
15.16
0.50
52.41
0.03
1.55
0.21
0.25
5.75
26.79
296.14
Northeastern Bering Sea
Neptunea ventricosa
N. heros
Pagurus trigoncheirus
Paralithodes camtschatica
P. platypus
Hyas coarctatus alutaceus
Chionoecetes opilio
Asterias amurensis
A. rathbuni
Evasterias echinosoma
Leptasterias polaris acervata
Lethasterias nanimensis
Strongylocentrotus droebachiensis
Gorgonocephalus caryi
Chelyosoma spp.
Styela rustica macrenteron
Halocynthia aurantium
Totals
Neptunea ventricosa
N. heros
Pagurus trigonocheirus
Paralithodes camtschatica
P. platypus
Hyas coarctatus alutaceus
Chionoecetes opilio
Asterias amurensis
A. rathbuni
Evasterias echinosoma
Leptasterias polaris acercata
Lethasterias nanimensis
Strongylocentrotus droebachiensis
Gorgonocephalus caryi
Chelyosoma spp.
Styela rustica macrenteron
Halocynthia aurantium
Totals
3.29
12.87
33.61
1.52
0.10
10.31
5.14
131.06
3.16
2.71
17.25
9.07
14.85
9.28
0.42
14.38
0.10
269.12
9.80
51.41
49.01
0.02
0.01
12.21
100.37
59.94
5.82
2.19
21.79
8.92
4.10
1.28
5.04
14.56
0.05
346.52
1.66
1.70
11.41
2.98
19.12
30.75
4.43
0.64
12.52
0.85
192.84
89.78
0.47
1.36
1.36
371.87
Southeastern Chukchi Sea
5.51
27.22
48.24
0.14
63.34
52.06
9.98
13.65
3.06"=
140.31
6.46
123.40
16.46
222.66
54.45
17.24
804.18
3.18
12.11
32.10
1.42
0.30
10.90
6.88
122.45
2.95
2.57
16.92
8.51
26.95
14.75
0.42
13.49
0.18
276.08
8.50
44.09
48.78
0.02
0.05
27.67
85.76
44.82
8.19
2.45
57.64
8.18
40.19
5.87
70.86
26.62
5.25
484.94
*Based on all stations examined.
''Stations were not sampled at depths greater than 100 m in the northeastern Bering Sea and southeastern Chukchi Sea.
■= Based mainly on one station at 42 m.
1138
Chukchi Sea. In nine Chukchi Sea stations biomasses
of N. heros were 0.6 g/m^ or greater. The highest
concentrations were in the 0-40 m stratum; these
showed mean values of 51.4 indiv./km and 13.4
percent of the total biomass. In particular, a station
90-100 km northwest of Shishmaref Inlet had a
Kpifaunal invertebrates 1 1 3i)
biomass of N. heros amounting to 11.4 g/m* and an
abundance of 1,190 indiv./km.
Red king crab, Paralithod.es camtschatica
The southeastern Bering Sea was clearly the most
important area for red king crab; they contributed
175
170°
165^^
160°
Figure 65-7. Distribution and biomass of the whelk Neptunea heros in the southeastern Bering Sea.
69-
170°
165°
160°
155°
69°
IVeptunea heros
Chukch.Sea
Biomass (Q/mM
_j
I^^^BI
KB
H
^^F~
- - —
n
• < 0.2
^^^^^^^1
30 JO 40 so <«■
0.2 S o < 0,4
0.4 < o < 0 6
0.6 •; Q
J
l^^^^^l
^^^^^^^H
1
. -J
^^^^^1
^^^^^^H
^m
■^H
68"
m . cT^
^
Hi
i
1
68'
67*
E
" 0 0 =
0 p
.H
^S
m
1
67°
66*
^
i
^
1
1
66°
170"
165°
160°
Figure 65-8. Distribution and biomass of the whelk
Neptunea heros in the northeastern Bering Sea.
Figure 65-9. Distribution and biomass of the whelk
Neptunea heros in the southeastern Chukchi Sea.
1140 Benthic biology
11 A percent of the total biomass. In this area accounted for only 2.3 percent of the total biomass.
king crab were present at nearly 33 percent of the Fewer than 6 percent of the Chukchi Sea stations
stations, most of which were in the southern portion contained king crab (Tables 65-3 and 65-4; Figs,
of the sampling area. This differs considerably 65-10 to 65-12).
from the northeastern Bering Sea, where P. cam-
In the southeastern Bering Sea Paralithodes cam-
tschatica was found at 48 percent of the stations but tschatica occurred mainly in waters deeper than
180°
175°
170°
165°
160°
155°
175'
170°
165°
160°
Figure 65-10. Distribution and biomass of the king crab Paralithodes camtschatica in the southeastern Bering Sea.
173' 171° 169° 167° 165° 163° 161° 159°
Figure 65-11. Distribution and biomass of the king crab
Paralithodes camtschatica in the northeastern Bering Sea.
Figure 65-12. Distribution and biomass of the king crab
Paralithodes camtschatica in the southeastern Chukchi Sea.
Epifaunal invertebrates 1141
40 m. The depth stratum > 40-100 m yielded the
highest mean g/m^ (0.9) and percentage of total
biomass (19.1). Values were slightly lower in the
deep-water stations (>100m). The mean density of
P. camtschatica in the southeastern Bering Sea was
only 8.2 crab /km. The greatest catch came from a
station 130 km northwest of Port MoUer in 65 m of
water. The king crab biomass and abundance here
were 68.3 g/m^ and 666 crab/km, respectively.
Snow (Tanner) crab Chionoecetes opilio
Chionoecetes opilio was one of the most ubiqui-
tous species, present in 65, 54, and 88 percent of the
stations in the southeastern Bering Sea, northeastern
Bering Sea, and southeastern Chukchi Sea, respective-
ly. Although widely distributed it was most impor-
tant in the epifaunal biomass in the southeastern
Bering Sea: 1.0 x g/m^ and 23.4 percent of the total
biomass. Stations at the >100m depth stratum
yielded the greatest biomass, 1.2 x g/m^ and 31.7
percent. The mean density of C. opilio in the south-
eastern Bering Sea was 135.6 crab/km. The greatest
concentration of C. opilio came from a station
approximately 300 km north of Unimak Pass in 71 m
of water. At this station 15.5 g/m^ and 3,288
crab/km were collected. Of the two northern
sampling areas, the Chukchi Sea was more abundant
in C. opilio, with 5.3 percent of the biomass as
compared with 0.4 percent in the northeastern Bering
Sea (Tables 65-3 and 65-4; Figs. 65-13 to 65-15).
Snow (Tanner) crab Chionoecetes bairdi
Chionoecetes bairdi was present only in the south-
eastern Bering Sea, and there it predominated at
stations deeper than 100 m. Stations immediately
north of Unimak Island had the greatest concentra-
tions; one station contained 15.5 g/m^ and 400
crab/km. The mean biomass and density were
0.4 g/m^ and 10.3 crab/km (Tables 65-3 and 65-4;
Fig. 65-16).
Sea star Asterias amurensis
Asterias amurensis was the most ubiquitous
species, occurring at 69, 81, and 68 percent of the
stations in the southeastern Bering Sea, northeastern
Bering Sea, and southeastern Chukchi Sea, respective-
ly. It was also the most important echinoderm, in
that it made up 14.1, 51.9, and 20.8 percent of the
biomass from the three areas, respectively. This sea
star was more commonly found in shallow water
(0-40 m). It accounted for 84.4 percent of the
biomass from the 0-40 m stratum in the southeastern
Bering Sea and 56.3 and 31.9 percent of the shallow-
water biomass from 0-40 m in the northeastern
Bering Sea and the southeastern Chukchi Sea, respec-
tively. The mean density of A. amurensis in these
three areas in shallow waters was 157.6, 131.1,
and 59.9 sea stars/km, respectively (Tables 65-3
and 65-4; Figs. 65-17 to 65-19). The area that
yielded the greatest concentrations was approxi-
mately 50 km southwest of Nome, where there were
14.9 g/m^ and 829 sea stars/km.
Sea star Euasterias echinosoma
Another dominant sea star was Euasterias echino-
soma. This species was most important in the north-
ern Bering and southeastern Chukchi seas, although
its mean density was only 2.6 and 2.4 sea stars/km,
respectively. It was most important in shallow-water
stations (0-40 m), although it did account for 4.1
percent of the biomass at stations >40-100 m deep in
the Chukchi Sea. The latter value was due mainly to
one station at 42 m. The shallow water (26 m)
southwest of Nome yielded the largest catch of
E. echinosoma: 4.0 g/m^ and 108 sea stars/km. This
species occurred at only 3.1 percent of the south-
eastern Bering Sea stations (Tables 65-3 and 65-4;
Figs. 65-20 to 65-22).
Sea star Leptasterias polaris acervata
The distribution of the sea star Leptasterias polaris
acervata was mainly restricted to depths of >40-100
m in the southeastern Bering and Chukchi seas,
although it occurred mainly at depths of 0-40 m in
the northeastern Bering Sea. The mean densities of
this sea star in the northeastern Bering Sea and
southeastern Chukchi Sea were 16.9 and 57.6 sea
stars/ km. The greatest catch of L. polaris acervata
occurred approximately 250 km north of Unimak
Pass, where 4.3 g/m^ and 148 specimens/km were
taken. The biomass of this sea star was most signifi-
cant in the southeastern Chukchi Sea, where it
represented 23.8 percent of the total biomass from
the >40-100-m stratum and 12.7 percent of the
biomass at all depths (Tables 65-3 and 65-4; Figs.
65-23 to 65-25).
Sea star Lethasterias nanimensis
Lethasterias nanimensis, like Leptasterias polaris
acervata, exhibited dissimilar depth distribution.
It mainly occurred at depths of 0-40 m in the two
northernmost sampling areas, but predominated at
>40-100 m in the southern Bering Sea. Lethasterias
nanimensis made up 7.1 and 6.4 percent of the
0-40 m biomass in the southeastern Chukchi Sea
and northeastern Bering Sea, respectively; but it
accounted for less than 0.3 percent of the biomass at
the > 40-1 00 m depth stratum in the southeastern
1142 Benthic biology
Bering Sea. The highest mean density, 8.5 sea stars/
km, occurred in the northeastern Bering Sea (Tables
65-3 and 65-4; Figs. 65-26 to 65-28). A station
approximately 80 km southwest of Nome contained
the greatest quantity of this sea star, 2.4 g/m^ and
151 sea stars /km.
Green sea urchin Strongylocentrotus droebachiensis
Strongylocentrotus droebachiensis was an impor-
tant component of the epifauna at stations >40-
100 m deep in the southeastern Chukchi Sea and
northeastern Bering Sea. The highest mean biomass
(0.9 g/m^ ) and density (192.8 urchins/km) came
180'
175°
170°
165°
160°
155'
175'
170°
165°
160°
Figure 65-13. Distribution and biomass of the snow crab Chionoecetes opilio in the southeastern Bering Sea.
69°
170°
165°
160°
155°
69"
Chia
Chu
Bion
1 -S
2^
noecetes opil
ch( Sea
ass (g/m' )
• < 1
o <2
O <3
_j
jHH^^^H
^^^^^^H
^^^^^H
0 80 ^-.. ^m
1
^
68°
3t
O
(. -'on.
A
V
^^H
68"
67°
i
L
I
^
H
67°
. . • o • . i
■
k^
\
>^^^^^B
66"
P
r
4
li
im
66°
170*
165°
160°
Figure 65-14. Distribution and biomass of the snow crab
Chionoecetes opilio in the northeastern Bering Sea.
Figure 65-15. Distribution and biomass of the snow crab
Chionoecetes opilio in the southeastern Chukchi Sea.
Epifaunal inverlebrales 1143
from depths of > 40-1 00 m in the northeastern Bering
Sea. Strongylocentrotus made up 15.1 and 22.4
percent of the biomass at deep-water stations in the
Chukchi Sea and northern Bering Sea, respectively
(Tables 65-3 and 65-4; Figs. 65-29 to 65-31). The
greatest concentration of these sea urchins came
from a station immediately north of the Bering Strait;
the biomass was 5.7 g/m^ , and the abundance was
1,267 urchins/km.
Basket star Gorgonocephalus caryi
Gorgonocephalus caryi was found in the south-
eastern Bering Sea in waters deeper than 40 m, but
was more abundant at depths >100m. It made up
7.2 percent of the biomass of the latter depth stratum.
In the northern portion of the Bering Sea and in the
southeastern Chukchi Sea it accounted for 56.1 and
7.7 percent of the biomass at >40-100m, respectively.
The mean density at > 40-1 00 m in the northeastern
Bering Sea was 89.8 indiv./km. The 0-40 m depth in
the southeastern Bering Sea was the only stratum
where this basket star did not occur; it accounted for
less than 3 percent of the biomass at all depths in the
southeastern Bering Sea (Tables 65-3 and 65-4; Figs.
65-32 to 65-34). A station immediately south of the
Bering Strait contained the greatest quantity of
G. caryi, 14.9 g/m^ and 562 indiv./km.
Tunicate Styela rustica macrenteron
Styela was found in all three study areas but was
most common in the southastern Bering Sea at
>40-100-m stations, where it made up 7.3 percent of
the biomass and had a mean density of 43.6 indiv./
km. Styela accounted for less than 1 percent of the
biomass in the northeastern Bering Sea and 2.1
percent of that of the Chukchi Sea (Tables 65-3 and
65-4; Figs. 65-35 to 65-37). The greatest catch of
Styela came from a station with a depth of 68 m in
the southeastern Bering Sea (57°39.0'N, 168°59.0'W);
here the biomass was 13.7 g/m^ and the abundance
was 1,671 indiv./km.
DISCUSSION
OCSEAP trawling surveys of 1975-76, which
covered most of the eastern Bering/Chukchi Sea
Figure 65-16. Distribution and biomass of the snow crab Chionoecetes bairdi in the southeastern Bering Sea.
1144 Benthic biology
continental shelf, revealed that commercial crabs and
sea stars dominate the epibenthic system (68.4
percent of the eastern Bering shelf epifaunal bio-
mass).
Populations of commercial crabs {Chionoecetes
spp. and Paralithodes spp.) account for 36.4 percent
of the eastern shelf epifaunal biomass, with the
highest concentrations of crabs occurring in the
southeastern portion of the shelf (96.1 percent of the
total commercial crab biomass), especially at depths
greater than 40 m. Recent catch statistics on com-
mercial crabs in Alaskan waters verify a crab-
180'
175'
170°
165°
160'
155°
175°
170
165°
160°
Figure 65-17. Distribution and biomass of the sea star Asterias amurensis in the southeastern Bering Sea.
175° 173° 171° 169° 167° 165
Figure 65-18. Distribution and biomass of the sea star
Asterias amurensis in the northeastern Bering Sea.
Figure 65-19. Distribution and biomass of the sea star
Asterias amurensis in the southeastern Chukchi Sea.
dominated epibenthic system in the southeastern
Bering Sea (Alaska Department of Fish and Game,
Kodiak, Alaska, and National Marine Fisheries
Service, Seattle, Washington). The 1979 southeastern
Bering Sea crab fishing season yielded a catch of 29.6
X 10^ mt of the snow crab Chionoecetes opilio;
Epifaunal invertebrates 1145
landings of another snow crab, C. bairdi, totalled 20.5
X 10^ mt. An additional 49 X 10^ mt of the red
king crab {Paralithodes camtschatica) were harvested
during the 1979-80 season. Only 2.8 X 10^ mt of the
blue king crab {P. platypus) were taken (near the
Pribilof Islands) in 1979.
175°
170°
165°
160°
Figure 65-20. Distribution and biomass of the sea star Evasterias echinosoma in tiie southeastern Bering Sea.
0,2 < O < 0,4
0.4 < O < 0.6
0.6 < Q
1 I I L
Figure 65-21. Distribution and biomass of the sea star
Evasterias echinosoma in the northeastern Bering Sea.
Figure 65-22. Distribution and biomass of the sea star
Evasterias echinosoma in the southeastern Chukchi Sea.
1146 Benthic biology
Low crab biomass values for the northeastern
Bering Sea and southeastern Chukchi Sea are re-
flected in commercial catch statistics. During the
1979 season, 1.4 X 10^ mt of Paralithodes cam-
tschatica were harvested north of Cape Newenham
and east of 168°W longitude, especially in the Norton
Sound area. The harvest of P. platypus amounted to
96 mt in 1979 in the region near St. Matthew Island.
There is no commercial crab fishing now in the
Chukchi Sea.
Sea stars were another dominant component of the
epifaunal biomass of the eastern Bering/Chukchi Sea
180°
175°
170°
165'
160'
155°
175'
170
165°
160°
Figure 65-23. Distribution and biomass of the sea star Leptasterias polaris acervata in tiie southeastern Bering Sea.
Figure 65-24. Distribution and biomass of the sea star
Leptasterias polaris acervata in the northeastern Bering Sea.
Figure 65-25. Distribution and biomass of the sea star
Leptasterias polaris acervata in the southeastern Chukchi
Sea.
shelf (32.0 percent of the total epifaunal biomass),
especially in the northeastern Bering Sea and south-
eastern Chukchi Sea, where they represented 67.5
and 45.3 percent, respectively, of the epifaunal
biomass. Asteroids made up only 15.3 percent of the
epifaunal biomass in the southeastern Bering Sea.
Epifaunal invertebrates 1147
Among the 29 sea-star species occurring along the
eastern Bering/Chukchi Sea shelf only 8 species were
common to the entire shelf region, and 4 of these,
Asterias amurensis, Euasterias echinosoma, Leptas-
terias polaris aceruata, and Lethasterias nanimensis,
were biomass dominants.
180°
175°
170°
165'
160'
155"
175°
170'
165°
160°
Figure 65-26. Distribution and biomass of the sea star Lethasterias nanimensis in the southeastern Bering Sea.
Figure 65-27. Distribution and biomass of the sea star
Lethasterias nanimensis in the northeastern Bering Sea.
Figure 65-28. Distribution and biomass of the sea star
Lethasterias nanimensis in the southeastern Chukchi Sea.
1148 Benthic biology
Asterias amurensis was the dominant sea star in all
three study regions; it occurred mainly in shallow
water (0-40 m). The species also occurs in shallow
waters in the Sea of Japan, Tatar Strait, the coasts of
South Sakhalin, the southern Kuril Islands, and the
northern Japan Sea (Pavlovskii 1966). It probably
also occurs along the western Bering and Okhotsk
seas. In the early 1950's A. amurensis caused exten-
sive damage to the flourishing shellfish culture
industry of Japan, inspiring biological studies of the
species (Hatanaka and Kosaka 1958).
Evasterias echinosoma was another dominant sea
180°
175°
170°
165°
160°
155'
175
170°
165°
160°
Figure 65-29. Distribution and biomass of the sea urchin Strongylocentrotus droebachiensis in the southeastern Bering Sea.
Figure 65-30. Distribution and biomass of the sea urchin
Strongylocentrotus droebachiensis in the northeastern
Bering Sea.
170°
165°
160°
155°
fi<)°
Strongylocentrotus droebachiens
' SHHl
^^^^■1
i^^^^^^^^^^r
^^^^^^H
Chukchi Sea
Biomass (g/m')
^^^^^H
's»;
1^ T ^ 5" ^ "" ^H
■ <0.1
0.1 «i 0 <0.2
0.2 < 0 < 0-3
J
M
^^^^1
w
c » M 40 » -,«> ^1
^H
68°
- -• s -
■<D^B
^M
^m
67-
it... ,4
-J\$^
. 1 .■ .
^Hj
^H
-W^' ' V!
■^
m
iSS
^^M
P^r' *"°is
m
■
imi^H
^^^H
1 r^ ^
^
■
nn
IIH
Figure 65-31. Distribution and biomass of the sea urchin
Strongylocentrotus droebachiensis in the southeastern
Chukchi Sea.
Epifaunal invertebrates 1149
star; its highest biomass was in the northern Bering
Sea and southeastern Chukchi Sea mainly in water
0-40 m deep. The eight stations where it occurred
in the southeastern Bering Sea, however, were at
depths between >40 and 100 m. Evasterias echino-
soma is the largest sea-star species known to occur in
the northern hemisphere. An average specimen
weighs 692 g (Feder and Jewett 1978), but specimens
up to 1,362 g and 70 cm in diameter have been
collected (Feder, unpublished observation).
A third dominant sea-star species, Leptasterias
polaris acervata, was most commonly found in the
180'
175°
170°
165°
160°
155"
Figure 65-32. Distribution and biomass of the basket star Gorgonocephalus caryi in tiie southeastern Bering Sea.
Figure 65-33. Distribution and biomass of the basket
star Gorgonocephalus caryi in the northeastern Bering Sea.
Figure 65-34. Distribution and biomass of the basket
star Gorgonocephalus caryi in the southeastern Chukchi
Sea.
1150 Benthic biology
southeastern Chukchi Sea. The depth distribution
of L. polaris acervata in the southeastern and north-
eastern Bering Sea was mainly > 40-100 m and
0-40 m, respectively. In the southeastern Chukchi
Sea, where it occurred in waters up to 100 m deep,
the highest biomass came from >40-100-m stations.
Unique among this species in the northern Bering Sea
and southeastern Chukchi Sea was the high occur-
rence of the endoparasitic gastropod Asterophila
japonica (Hoberg et al. 1980). Parasitized L. polaris
acervata were observed at 7 widely dispersed stations
in Norton Sound and 11 concentrated stations in the
180'
175'
170°
165°
160°
155'
Figure 65-35. Distribution and biomass of the tunicate Styela rustica macrenteron in the southeastern Bering Sea.
170°
165°
160°
155°
69°
Styeta rustics macrenteron
Chukchi Sea
''^^M
69°
^^^^^1
„ H
Biomasi (9/m' )
^^^^^^^1 1 ^
' ' ^H
• <0.14
0.14 < 0 < 0.28
^^^^^H
- 1
0.28 < 0 < 0.42
0.42 •; Q
Jj^l
68"
V
0 >-'^^^^^^^H
68"
67°
fc .'
• . • ■ ■ '
67°
66°
66"
170"
165°
160°
Figure 65-36. Distribution and biomass of the tunicate
Styela rustica macrenteron in the northeastern Bering Sea.
Figure 65-37. Distribution and biomass of the tunicate
Styela rustica macrenteron in the southeastern Chukchi
Sea.
Epifaunal invertebrates 1151
Chukchi Sea/Kotzebue Sound area; the mean percen-
tages of parasitized specimens in the respective areas
were 15 percent and 10 percent.
Distribution of Lethasterias nanimensis was similar
to that of Leptasterias polaris aceruata; it was concen-
trated in the northeastern Bering Sea and south-
eastern Chukchi Sea and displayed varying depth
distributions. It mainly occurred in 0-40 m water in
the two northern areas but was found mostly in water
> 40-1 00 m deep in the southeastern Chukchi Sea.
The great abundance and broad distribution of sea
stars, primarily Asterias amurensis, Euasterias echino-
soma, Leptasterias polaris aceruata, and Lethasterias
nanimensis, in the eastern Bering and Chukchi seas
suggest that a common and widely distributed prey
must be available. Bivalves (e.g., Tellina lutea,
Clinocardium ciliatum, Cyclocardia spp., Spisula
polynyma, and Serripes groenlandicus), potential
sea-star prey, are broadly distributed throughout
the shelf areas inhabited by the above-mentioned sea
stars (McDonald et al., Chapter 66, this volume, give
data and maps of the distributions and abundance
of clams in the southeastern Bering Sea). It was
estimated by Hatanaka and Kosaka (1958) that in
Sendai Bay, Japan, food (primarily clams) consumed
annually by A. amurensis amounted to about 8 X 10^
mt; this value approximates the 10 X 10^ mt of food
(primarily clams) consumed annually by bottom
fishes. If the food requirements are similar for sea
stars, commercial crabs, and bottom fishes in the
Bering Sea, the size of sea-star populations clearly
has an important bearing on the production of useful
crabs and fishes in the eastern Bering Sea.
An increase in numbers of sea-star species with
direct development in cold water is documented by
Feder and Christensen (1966) and Boolootian (1966)
(see also Mileikovsky 1971 for a review of types of
larval development and their ecological significance).
Reproductive data for sea stars of Alaskan waters are
currently too fragmentary to generalize for species
here; however, some data for two species of sea stars
(Leptasterias arctica and L. polaris aceruata) occur-
ring in the northeastern Bering and southeastern
Chukchi seas are included in Feder and Jewett
(1978). These species utilize direct development in
the northern waters aind were observed brooding in
September and October (Feder and Jewett 1978).
Leptasterias arctica were brooding a few relatively
large eggs in the oral area at this time; L. polaris
aceruata were brooding young during the same
period. The fact that young L. polaris aceruata were
always attached to the shells of a clam (Macoma) or a
snail (Natica) may reflect scarcity of suitable egg
attachment surfaces.
Of the 11 dominant epifaunal species considered in
this chapter, 7 {Neptunea heros, Asterias amurensis,
Euasterias echinosoma, Leptasterias polaris aceruata,
Lethasterias nanimensis, Strongylocentrotus droe-
bachiensis, and Gorgonocephalus caryi) had their
highest biomass values in the northeastern Bering and
southeastern Chukchi seas. Stoker (1978; Chapter
62, this volume) also noted that the highest infaunal
biomass values were near the Bering Strait, and attrib-
uted this to (l)high rates of primary productivity
near the Bering Strait in early to late spring, (2) in-
flux of terrestrial detritus from the Yukon River,
(3) water-current structures of the Bering and Chukchi
seas, and (4) temperature restriction of bottom-feeding
fishes. Presumably, the factors responsible for high
infaunal biomass in the strait region are also respon-
sible for the high biomass of these seven epifaunal
species. Paramount among these factors is the
reduction in competition for food as a result of low
water temperatures on the northern shelf which
usually preclude invasion of benthic-feeding fishes.
However, occasional warming trends may allow the
fishes to forage in the infauna-rich northern waters
(Jewett and Feder 1980). Predation by Pacific walrus
is low in the northeastern Bering and southeastern
Chukchi seas: these mammals feed mainly in the
southeastern Bering and northeastern Chukchi
seas and feed very little while migrating through the
northeastern Bering and southeastern Chukchi seas
(Stoker, Chapter 62, this volume). Predation by king
and snow crabs on the infaunal benthos is also low at
these northern latitudes, since their population levels
are low. Although infaunal predation by crabs,
fishes, and marine mammals is low, year-round
predation by one important group, sea stars, does
occur. The extent of the infaunal food resources
taken from this region by these organisms is un-
known; however, it is assumed that they are primarily
utilizing large bivalve mollusks and epifaunal organ-
isms as they do elsewhere (Feder and Christensen
1966; Sloan 1980; Feder and Jewett, Chapter 69, this
volume). The effect of sea stars on the dynamics
of the benthic system of northern Alaska waters is
yet to be determined.
There is now a reasonably satisfactory body of
knowledge, on a regional basis for the months sam-
pled, of the distribution, abundance, and biomass of
the major epifaunal invertebrates of the shelf of the
eastern Bering and Chukchi seas, but we need more
seasonal data. Comparable data for the infauna
are required. Relevant infaunal data, useful for
comparison, from the southeastern Bering Sea are
available in Feder et al. (1980) and Haflinger (1978),
and an intensive investigation of the infauna of the
1152 Benthic b io logy
northeastern Bering and southeastern Chukchi seas is
reported in Stoker (1978). Further investigations of
the infauna of the northern shelf regions from areas
of ecological interest, primarily near proposed petro-
leum lease areas, are in progress (Feder and Jewett,
unpub. data). When information from further study
is available, a reasonable biological assessment of the
effect of petroleum-related activities in these areas
can be made.
ACKNOWLEDGMENTS
This study was supported under contract #03-5-
022-56 between the Institute of Marine Science
(Howard M. Feder, principal investigator) of the
University of Alaska and NOAA, Department of
Commerce, through the Outer Continental Shelf
Environmental Assessment Program, to which funds
were provided by the Bureau of Land Management,
Department of the Interior. This is Contribution
No. 431, Institute of Marine Science, University of
Alaska, Fairbanks.
Feder, H. M., and A. M. Christensen
1966 Aspects of asteroid biology. In:
Physiology of Echinodermata, R. A.
Boolootian, ed., 87-127. John Wiley
and Sons, N. Y.
Feder, H. M., K. E. Haflinger, M. Hoberg, and J.
McDonald
1980 The infaunal invertebrates of the
southeastern Bering Sea. Final
Rep. to NOAA, R.U. #5.
Feder, H. M., and S. C. Jewett
1978 Survey of the epifaunal invertebrates
of Norton Sound, southeastern
Chukchi Sea, and Kotzebue Sound.
Inst. Mar. Sci. Rep. R78-1. Univ.
of Alaska, Fairbanks.
1980 Survey of the epifaunal invertebrates
of the southeastern Bering Sea with
notes on the feeding biology of
selected species. Inst. Mar. Sci. Rep.
R78-5, Univ. of Alaska, Fairbanks.
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Alton, M. S.
1974
Bering Sea benthos as a food resource
for demersal fish populations. In:
Oceanography of the Bering Sea,
D. W. Hood and E. J. Kelley, eds.,
257-77. Inst. Mar. Sci., Occ. Pub.
No. 2, Univ. of Alaska, Fairbanks.
Boolootian, R. A.
1966 Reproductive physiology. In:
Physiology of Echinodermata, R. A.
Boolootian, ed., 561-613. John Wiley
and Sons, N. Y.
EUson, J. G., B. Knake, and J. Dassow
1949 Report of Alaska exploratory fishing
expedition, fall of 1948, to northern
Bering Sea. U.S. Fish Wildl. Serv.,
Fish. Leafl. 342:25.
Feder, H. M., and G. J. Mueller
1974 Biological studies. In: Environ-
mental study of the marine environ-
ment near Nome, Alaska, 31-85. Inst.
Mar. Sci. Rep. R74-3, Univ. of Alaska,
Fairbanks.
Fishery Market News
1942 The Alaskan king crab.
Market News 4:105.
Fishery
Haflinger, K. E.
1978 A numerical analysis of the distribu-
tion of the benthic infauna of the
southeastern Bering Sea shelf. Mas-
ter's Thesis, Univ. of Alaska, Fair-
banks.
Ellson, J. G., D. Powell, and H. H. Hildebrand
1950 Exploratory fishing expedition to the
northern Bering Sea in June and July,
1949. U.S. Fish Wildl. Serv., Fish.
Leafl. 369:56.
Hatanaka, M., and M. Kosaka
1958 Biological studies on the population
of the starfish, Asterias amurensis, in
Sendai Bay. Tohoku J. Agric. Res.
9:159-78.
Epifaunal invertebrates 1 1 53
Hoberg, M. K.
1980
Hughes, S. E.
1979
, H. M. Feder, and S. C. Jewett
Some aspects of the biology of the
parasitic gastropod, Asterophila
japonica Randall and Heath (Proso-
branchia: Melanellidae), from south-
eastern Chukchi Sea and northeastern
Bering Sea, Alaska. Ophelia 19:73-7.
and R. W. Nelson
Distribution, abundance, quality and
production fishing studies on the surf
clam, Spisula polynyma, in the
southeastern Bering Sea, 1978.
NWAFC Proc. Rep. 79-4.
Pereyra, W. T., J. E. Reeves, and R. G. Bakkala
1976 Demersal fish and shellfish of the
eastern Bering Sea in the baseline year
1975. U.S. Dep. Comm. NOAA Nat.
Mar. Fish. Serv., NWAFC Proc. Rep.
Semenov, V. N.
1964 Quantitative distribution of benthos
on the shelf of the southeastern
Bering Sea. In: Soviet fisheries
investigations in the northeast Pacific,
P.A. Moiseev, ed., 3:167-75. (Israel
Prog. Sci. Transl., 1968.)
I
Jewett, S. C, and H. M. Feder
1980 Autumn food of adult starry floun-
ders, Platichthys stellatus, from the
northeastern Bering Sea and the
southeastern Chukchi Sea. J. Cons,
int. Explor. Mer 39:7-14.
McLaughlin, P. A.
1963 Survey of the benthic invertebrate
fauna of the eastern Bering Sea.
U.S. Fish. Wildl. Serv. Spec. Sci. Rep.,
Fish. No. 401.
Merriam, C. H., editor
1904 Harriman Alaska expedition. Double-
day, Page and Co., N. Y.
Mileikovsky, S. A.
1971 Types of larval development in marine
invertebrates, their distribution and
ecological significance: A re-evalua-
tion. Mar. Biol. 10:193-213.
Neiman, A. A.
1963 Quantitative distribution of benthos
on the shelf and upper continental
slope in the eastern part of the Bering
Sea. In: Soviet fisheries investigations
irv'the northeast Pacific, P.A. Moiseev,
' ed., 1:143-217. (Israel Prog. Sci.
Transl., 1968.)
Pavlovskii, E. N.
1966 Atlas of the invertebrates of the Far
Eastern seas of the USSR. (Israel
Prog. Sci. Transl.)
Sloan, N. A.
1980 Aspects of the feeding biology of
asteroids. Oceanogr. Mar. Biol.
Ann. Rev. 18:57-124.
Sparks, A. K., and W. T. Pereyra
1966 Benthic invertebrates of the south-
eastern Chukchi Sea. In: Environ-
ment of the Cape Thompson Region,
Alaska, N. J. Wilimovsky and J. N.
Wolfe, eds., 2:817-38. U.S. Atomic
Energy Comm., Oak Ridge, Tenn.
Stoker, S. W.
1978 Benthic invertebrate macrofauna of
the eastern continental shelf of
the Bering and Chukchi seas. Ph.D.
Dissertation, Inst. Mar. Sci., Univ. of
Alaska, Fairbanks.
Wigutoff, N. B., and C. B. Carlson
1950 S.S. Pacific Explorer, V. 1948 Opera-
tions in the North Pacific and Bering.
Wolotira, R. J., Jr., T. M. Sample, and M. Morin, Jr.
1977 Demersal fish and shellfish resources
of Norton Sound, the southeastern
Chukchi Sea and adjacent w^aters in
the baseline year 1976. NWAFC Proc.
Rep.
Bivalve Mollusks of the Southeastern Bering Sea
J. McDonald, H. M. Feder, and M. Hoberg
Institute of Marine Science
University of Alaska
Fairbanks
ABSTRACT
Bivalve mollusks and other infaunal species of the south-
eastern Bering Sea shelf have patchy distributions. The
distribution of the bivalves Nucula tenuis, Nuculana fossa,
Yoldia amygdalea, Macoma calcarea. Tellina lutea, Clino-
cardium ciliatum, Cyclocardia crebricostata, and Spisula
polynyma is associated with specific sediment size, sorting
ranges, percentage of mud, and depth. There is little differ-
ence in the growth rates of Nucula tenuis, Nuculana fossa,
Yoldia amygdalea, Spisula polynyma, Tellina lutea, and
Macoma calcarea over the southeastern Bering Sea shelf.
Mortality between year -classes for each species of clam v£u:ies
significantly at specific ages. The variation in year-class
composition of specific stations indicates variable annual
recruitment success of different areas on the shelf. The data
presented here support Neiman's age-composition hypothesis,
which suggests that the prevalence of older bivalve mollusks in
the middle zone of the eastern Bering Sea results from the
exclusion of predatory bottom fishes by the low winter water
temperatures.
INTRODUCTION
Bivalve mollusks are among the dominant infauna
of the shelf of the southeastern Bering Sea with 128
described species (N. Foster, personal communica-
tion) and as many as 3,380 individuals observed per
m^ (Feder et al. 1980). Clams and cockles are an
important link in benthic food webs, leading to snow
(Tanner) crabs (Chionoecetes spp.), king crabs
{Paralithodes spp.), and flatfishes in some regions of
the Bering Sea (Feder and Jewett, Chapter 65, this
volume; Neiman 1964; Pereyra et al. 1976). It has
been suggested that predators control the densities
and age composition of bivalve populations in the
southeastern Bering Sea (Neiman 1964). A Russian
survey of the southeastern Bering Sea in 1961 re-
ported that the benthos, including bivalve mollusks,
utilized as food by flatfishes was most abundant in
the middle portion of the southeastern shelf (Fig.
66-1) (Neiman 1963). Neiman (1964) looked at four
species of bivalves from the southeastern Bering Sea
and found that they generally had a lifespan of one
to six years. A large percentage of them were be-
tween four and six years old. Because of the pre-
ponderance of these older mollusks, she suggested
that the middle shelf is probably not used extensively
by higher trophic levels and that such predators as
flatfishes may be excluded from this region for a large
part of the year by low bottom-water temperatures.
Additional data are needed to further examine the
relationships between bivalve mollusks and their
predators as well as to comprehend the biology and
distribution of bivalves in the southeastern Bering
Sea.
Bivalve mollusks are more useful than most in-
faunal organisms for examining long-term conditions
that have occurred in a benthic system. Bivalves are
long-lived and readily collected and preserved, and
their shells typically show annual growth rings the
widths of which reflect environmental conditions
Figure 66-1. Three regions of the eastern Bering Sea
(modified from Sharma 1972).
1155
1156 Ben th ic b iology
existing at the time of their formation. Thus, the
shells of bivalves show well-preserved growth histories
of their biological responses to varying environmental
conditions.
DESCRIPTION OF THE AREA
The Bering Sea is an extension of the North
Pacific, separated from it by the Aleutian and
Komandorsky islands system and the Alaska Penin-
sula (Takenouti and Ohtani 1972). The sill depths
between the western islands often exceed 4,000 m
(Filatova and Barsanova 1964), permitting nearly
unrestricted exchange of waters with the north
Pacific. In contrast, the exchange with the Arctic
Ocean is limited to the Bering Strait, where the sill
depth is less than 50 m. Thus, the fauna of the
Bering Sea is predominantly of Pacific origin, with
arctic forms limited to shallow-water organisms that
can pass through the Bering Strait (Stoker 1973,
1978).
The Bering Sea circulation south of St. Lawrence
Island forms a counterclockwise gyre with Pacific
water entering through the Aleutian passes and
moving generally north along the eastern side of the
Bering Sea, thus endowing the eastern shelf with
warmer bottom temperatures than the western side
(Filatova and Barsanova 1964, Stoker 1978).
The submarine topography of the eastern Bering
Sea shelf is uniformly level except for submarine
canyons at the shelf break and a few shallow depres-
sions. The average slope is approximately 1 m/3 km.
The distribution of the sediments is controlled
primarily by dominant currents and seasonal weather
patterns.
The eastern Bering Sea shelf can be divided into
five regions (Fig. 66-1) (Sharma 1972), only three of
which, each with its own sediment characteristics
and distributions, are relevant to this report (Figs.
66-2 to 66-6): the southeastern shelf, including
Bristol Bay; the central shelf, a broad region lying
between St. Matthew and Nunivak islands; and the
outer shelf, an area oriented north-south, parallel to
the continental margin (Nelson et al. 1972).
The southeastern Bering shelf is bounded on the
north and the east by the southern portions of the
Kilbuck Mountains and on the south by the Alaska
Peninsula. The drainage of numerous rivers and lakes,
notably the Nushagak and Togiak rivers from the
north and the Kvichak River from the east, deposits
sediments on the shelf. The bottom morphology
consists of a series of banks in the north and shallow
depressions along the Alaska Peninsula. The near-
shore sediments consist of well- to poorly sorted
gravel and coarse sand (—0.77-1.00) with moderately
to poorly sorted, medium to fine sand (1.25-3.00)
deposited on the mid -shelf of this region. Very
poorly sorted silt and clay fractions (4.25-6.00)
are deposited farther offshore (Figs. 66-2 to 66-6)
(Sharma 1972, 1975; Sharma et al. 1972).
The central Bering shelf extends from the
Kuskokwim Delta north to the southern end of the
Yukon Delta and the shores of St. Lawrence Island.
Sediments from the Kuskokwim River, St. Matthew
and Nunivak islands, and the adjacent coast are
deposited on the shelf. Nearshore sediments are well-
to poorly sorted gravel and sand (—0.77-1.00), mid-
shelf sediments are primarily poorly sorted seinds
(0.25-3.00), and offshore sediments are poorly to
very well sorted silt and clay fractions (4.25-6.00)
(Figs. 66-2 to 66-6) (Hoskin 1978; Sharma 1972,
1975; Sharma et al. 1972).
The outer Bering shelf parallels the continental
margin. The bottom contour is steepest near the
Pribilof Islands and slopes gradually to the north. At
the southern extent of the outer Bering shelf, north
of Unimak Island, the shelf is about 120 km wide; as
it extends north it narrows near the Pribilof Islands
but widens again to a maximum width of 350 km
near the Gulf of Anadyr. Sediments in general are
moderately to very poorly sorted (Fig. 66-6). Sands
are predominant at lesser depths (1.0-4.00); silt
and clay fractions (4.25-6.00) are deposited in
mid-region and farther offshore (Figs. 66-2 to 66-6)
(Sharma 1972, 1975; Sharma et al. 1972). Multiple
sediment sources and intermixing increase the com-
plex sediment distribution in the outer Bering shelf.
Sediments from the southern portions of the outer
shelf are dominated by detrital materials originating
in the Bristol Bay and Kuskokwim River drainages
(Sharma 1972). The central portion of the outer
Bering shelf is covered by sediments from the adja-
cent coast, offshore islands, and the Kuskokwim
River. There is more organic matter in the outer
Bering shelf sediments than in sediments from the
southeastern and central shelves (Sharma 1972, 1975;
Sharma et al. 1972).
In general, sediment particle size in the three shelf
regions decreases with increasing depth and distance
from shore (Fig. 66-1). Suspended load in the water
column varies seasonally. During the period of ice
cover, the suspended load of surface water is low, but
it increases during spring phytoplankton blooms.
After storms, suspended load increases because
bottom material is resuspended by wave action (see
Sharma 1972; Rees et al. 1977; Sanders 1958, 1960
for discussions). Twenty mg/1 of sediment in the
near-bottom waters have been reported (Lisitsyn
1966).
Bivalve mollusks 1157
176"
172°
168°
164°
160°
156°
Figure 66-2. Distribution of sediment size (mean phi) in the southeastern Bering Sea.
DISTRIBUTION, ABUNDANCE, AND
BIOMASS OF BIVALVES
The distribution of bivalves of the southeastern
Bering Sea shelf was incompletely known before
Outer Continental Shelf Environmental Assessment
Program (OCSEAP) investigations. Past investigations
of Bering Sea bivalves were centered primarily in the
vicinity of the Gulf of Anadyr (see Feder et al. 1977
for literature review). Recent investigations of the
infauna, including studies of bivalve mollusks (Stoker
1978, Haflinger 1978, McLaughlin 1963, Rowland
1973) from the southeastern and northeastern Bering
Sea, are also available. Rowland (1973) includes a
discussion of the distribution of clams in relation to
sediment parameters.
Methods
Samples were collected by van Veen grab from the
NOAA ships Discoverer and Miller Freeman in 1975
(Feder et al. 1980, Feder and Jewett 1980), otter
trawl from the Miller Freeman in 1975 and 1976,
clam dredge from F/V Smaragd in 1977, and pipe
dredge (0.7 X 0.5 m) in 1976 from the Miller
1158 Benthic biology
176°
172°
168°
164°
160°
156°
Figure 66-3. Distribution of sand fractions in tiie soutiieastern Bering Sea.
Freeman (Feder et al. 1980, Feder and Jewett 1980)
(Fig. 66-7). A stainless steel screen with a mesh of
1 mm^ was inserted at the base of the pipe dredge on
sandy bottom; screen with a mesh of 2 mm^ was used
on fine sediments. Samples were washed over a
1-mm^ screen. Sediments collected from van Veen
grab samples were analyzed by Hoskin (1975,1978).'
Values, based on Hoskin (1975, 1978), of mean
sediment size, distribution of gravel, percentage of
sand, percentage of mud, and sorting characteristics
are included in Table 66-1 (see also Fig. 66-7 and
Table 66-2), and illustrated in Figs. 66-2 to 66-6. The
infauna taken by van Veen grab was analyzed by
Feder et al. (1980) and Haflinger (1978); the data are
The grade scale often used in tiie past for sediments is thie
Wentwortii scale, a logaritiimic scale of sizes in millimeters.
The 0 scale, devised by Krumbein (see Pettijohn 1957) is a
much more convenient way of presenting data and is used
almost entirely in recent work. Phi (0) is the negative logar-
ithm (to the base 2) of the diameter of particles. To avoid
negative numbers for the various sand grades and finer material
the log was multiplied by —1, or phi = 2~log2 diameter (mm).
Phi values represent the inverse of any mean sediment size,
e.g., gravel = > -10 (Folk 1974, Folk and Ward 1975, Pettijohn
1957) (Tables 66-1 and 66-2).
Bivalve mollusks 1159
156°
Figure 66-4. Distribution of gravel in the southeastern Bering Sea.
reported as density (no./m^ ) and biomass (g/m^ ).
Eight of the most common species of bivalve
mollusks collected— A/^ucu /a tenuis, Nuculana fossa,
Yoldia amygdalea, Cyclocardia crebricostata, Clino-
cardium ciliatum, Spisula polynyma, Tellina lutea,
and Macoma calcarea — were selected for detailed
study. Tellina lutea and Spisula polynyma, although
not frequently taken or collected quantitatively
with the gear used, are included because of their
potential commercial value; they were commonly
taken by hydraulic clam dredge (Hughes and Bourne,
Chapters?, this volume; Feder et al. 1978a). All
calculations and distribution maps for the eight
bivalve species are based on 1975 infaunal collections
(Feder et al. 1977, Feder et al. 1980, Haflinger
1978). A compilation of density and biomass data
for all other species of pelecypods collected by van
Veen grab and pipe dredge in the study is also pre-
sented. Density and biomass figures for all species are
available at the National Oceanographic Data Center.
The percentage of the total number and biomass of
each of the eight species of clams collected by grab is
calculated relative to (1) sediment size (phi, 0),
(2) sorting, and (3) depth range.
1160 Ben th ic b iology
176
•)4'
I7S«
Figure 66-5.
166° I64' 160°
Distribution of mud fractions in the southeastern Bering Sea.
Two types of maps are included for each species of
clam {except Spisula poly ny ma): a total distribution
for each species of clam taken by all gear (grab, pipe
dredge, clam dredge, trawl) used on cruises by Feder
and associates (Feder et al. 1978b), and a quantitative
distribution of each species of clam taken by grab in
1975 (Feder etal. 1980).
RESULTS
Thirty-three species of bivalve mollusks were
collected on the southeastern Bering Sea shelf (Table
66-3).
Nucula tenuis was broadly distributed (Fig. 66-8)
over the southeastern Bering Sea shelf with greatest
abundance at Stations 1, 11, 12, 18, 19, 28, 29, 30,
63, 71, 72, 82, 83, 935, 937, 939, and 942 (Figs.
66-8, 66-9, and 66-10; Table 66-4). It was present at
77 percent of the stations sampled by van Veen grab,
in greatest biomass at Stations 19, 28, 29, 63, 71, 83,
and 935 (Table 66-4). It was associated with sedi-
ment types ranging from fine sand to medium silt
(2.25-5.70; Tables 66-1 and 66-2, Figs. 66-3 to 66-6;
Table 66-5). Major Component of Collection:
Ninety-one percent of N. tenuis collected occurred in
fine sand to medium silt (3.0-5.00); 75 percent of the
Bivalve mollusks 1161
< .35 Very well sorted
I I .35 ■ .50 Well sorted
23 > .50 ■ .71 Moderately well sorted
II I ll>.71 • 1.0 Moderately sorted
1.0 2.0 Poorly sorted
2.0 - 4.0 Very poorly sorted
(66' l«4." 160°
Figure 66-6. Sediment sorting in the southeastern Bering Sea.
ims were at sediment sorting values from >1.0 to
0 (Table 66-6). Ninety-two percent of N. tenuis
is collected at 50-100 m (Table 66-7). Minor
ymponent of Collection: Nine percent of iV. tenuis
IS collected in either fine sand (3-80) or medium silt
.70); 3 percent was at sediment sorting values of
3.35, 4 percent at 0.35-0.50, 8 percent at 0.71-1.0,
id 10 percent at 2.0-4.0. One percent of N. tenuis
:curred at a depth <25 m (coarse sand), 1 percent at
)-50 m (fine sand), and 6 percent at 100-150 m
ledium silt).
Nuculana fossa was well distributed over the outer
)rtion of the southeastern shelf and part of the
outer shelf (Figs. 66-1, 66-2, and 66-10). The greatest
abundance of this species occurred at Stations 18, 28,
29, 36, 47, 49, 64, 65, 70, 71, and 72 (Figs. 66-2 and
66-11; Table 66-4). It was present at 36 percent of
the stations sampled by van Veen grab. The greatest
biomass occurred at Stations 29, 47, 64, and 71
(Table 66-4). Nuculana fossa was associated v^rith
sediment types ranging from fine sand to medium silt
(3.0-5.70; Tables 66-1 and 66-2, Figs. 66-2 to 66-6,
66-10, and 66-11, Table 66-5). Major Component of
Collection: Eighty-four percent of A'^. fossa occurred
in very fine sand to medium silt (4.0-5.00) with 96
percent of the clams at sediment sorting values from
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1163
TABLE 66-2
A comparison of five methods used to describe sediments (Folk 1974)
U.S. Standard
sieve mesh no.
Millimeters
(1 Kilometer)
Microns
Phi (0)
Wentworth size-class
>
Si
O
T3
C
3
Use
wire
squares
5
6
7
8
10
12
14
16
18
20
25
30
35
1/2
40
45
50
60
1/4
70
80
100
120
1/8
140
170
200
250
1/16
270
325
1/32
Analyzed
1/64
1/128
by
1/256
Pipette
or
Hydrometer
4096
1024
256
64
16
4
3.36
2.83
2.38
2.00
1.68
1.41
1.19
1.00
0.84
0.71
0.59
0.50
0.42
0.35
0.30
0.25
0.210
0.177
0.149
0.125
0.105
0.088
0.074
0.0625
0.053
0.044
0.037
0.031
0.0156
0.0078
0.0039
0.0020
0.00098
0.00049
0.00024
0.00012
0.00006
-20
-12
-10
-8
Boulder (—8 to —120)
-6
Cobble (—6 to —80)
-4
Pebble (-2 to —60)
-2
Pebble (-2 to -60)
-1.75
Granule
-1.5
Granule
-1.25
Granule
-1.0
Granule
-0.75
Very coarse sand
-0.5
Very coarse sand
-0.25
Very coarse sand
0.0
Very coarse sand
0.25
Coarse sand
0.5
Coarse sand
0.75
Coarse sand
500
1.0
Coarse sand
420
1.25
Medium sand
350
1.5
Medium sand
300
1.75
Medium sand
250
2.0
Medium sand
210
2.25
Fine sand
177
2.5
Fine sand
149
2.75
Fine sand
125
3.0
Fine sand
105
3.25
Very fine sand
88
3.5
Very fine sand
74
3.75
Very fine sand
62.5
4.0
Very fine sand
53
4.25
Coarse silt
44
4.5
Coarse silt
37
4.75
Coarse silt
31
5.0
Medium silt
15.6
6.0
Medium silt
7.8
7.0
Fine silt
3.9
8.0
Very fine silt
2.0
9.0
Clay (some use 2n or
0.98
10.0
90 as the clay
0.49
11.0
boundary)
0.24
12.0
0.12
13.0
0.06
14.0
1164
176°
172°
168°
164°
160°
156°
Figure 66-7. Infaunal stations occupied in the eastern Bering Sea, May 1976.
Nucula tenuis
Nuculana fossa
Yoldia amygdalea
Y. myalis
Y. scissurata
Y. montereyensis
Musculus niger
Dacrydium vitreum
TABLE 66-3
Thirty -three species of bivalve mollusks collected on the
southeastern Bering Sea shelf by van Veen grab and pipe
dredge (Feder et al. 1980)
Thyasira flexuosa Clinocardium ciliatum
Axinopsida serricata C. fucanum
Diplodonta aleutica Spisula polynyma
Mysella planata Siliqua alta
Cyclocardia crebricostata Tellina lutea
Astarte borealis Macoma calcarea
A. montegui M. moesta moesta
Serripes groenlandicus M. crassula
M. lama
M. corrugatus
Liocyma fluctuosa
My a priapus
Hiatella arctica
Lyonsia norvegica
Pandora glacialis
Thracia sp.
Periploma alaskana
1165
1166 Benthic biology
176°
172°
168°
164°
160°
156°
Nucula tenuis
54° -
Figure 66-8. Distribution of Nucula tenuis based on collections taken with a grab, pipe dredge, clam dredge, and otter
trawl.
>1.0 to 2.0 (Table 66-6). Ninety-six percent of
N. fossa occurred at 75-125 m (Table 66-7). Minor
Component of Collection: Twelve percent of the
clams occurred in fine to very fine sand (3.0-4.00)
and 4 percent in medium silt (5.70) with 1 percent of
the species at sediment sorting values of >0. 71-1.0
and 3 percent at > 2.0-4.0. Four percent of N. fossa
occurred at depths of 50-75 m (medium silt) and
2 percent at 150->175 m (medium silt).
Yoldia amygdalea was present on the central and
northwestern portions of the southeastern shelf and
north and south on the central shelf (Figs. 66-1,
66-12, and 66-13). The greatest abundance of this
species occurred at Stations 63, 64, 70, 70A, 71, and
72 (Figs. 66-12 and 66-13; Table 66-4). It was
present at 23 percent of the stations sampled by van
Veen grab. The greatest biomass occurred at Sta-
tions 63, 64, 70, 71, 72, 82, 83, and 937 (Table
66-4). Yoldia amygdalea was associated with sedi-
ment types ranging from medium sand to medium silt
(2.0-5.70; Tables 66-1 and 66-2, Figs. 66-2 to 66-6,
66-12, and 66-13, Table 66-5). Major Component of
Bivalve mollusks 1167
180°
175'
170°
165°
160"
155'
175'
170°
165°
160'
Figure 66-9. Qualitative distribution of Nucula tenuis taken in the southeastern Bering Sea by van Veen grab (Feder et al.
1980).
Collection: Eighty-nine percent of Y. amygdalea
occurred in very fine sand to medium silt (4.0-5.00)
with 89 percent of the clams at sediment sorting
values from 1.0 to 2.0 (Table 66-6). Ninety-two
percent of Y. amygdalea occurred from 50 to 100 m
(Table 66-7). Minor Component of Collection: One
percent of the clams occurred in medium to fine
sand (2.0-3.00), 3 percent in fine to very fine sand
(3.0-4.00) and 7 percent in medium silt (5.70) with
3 percent of the species at sediment sorting values
of 0.35-0.50, 1 percent at > 0.7 1-1.0, and 7 percent at
> 2. 0-4.0. Seven percent of Y. amygdalea occurred at
depths of 100-125 m and 1 percent at 150->175m
(medium silt).
Macoma calcarea was mainly distributed on the
southern portion of the southeastern shelf but
extended north and west into the outer shelf and
immediately adjacent to the central shelf (Figs. 66-1,
66-14, and 66-15). The greatest abundance of this
species occurred at Stations 10, 12, 28, 45, 63,
64, 65, 70A, 71, and 83 (Figs. 66-1, 66-14, and
66-15; Table 66-4). The species was present at 23
percent of the stations sampled by van Veen grab.
The greatest biomass occurred at Stations 10, 22,
45, 63, and 64. Macoma calcarea was associated with
sediment types ranging from medium sand to medium
silt (2.0-5.70; Tables 66-1 and 66-2; Figs. 66-2 to
66-6, 66-14 and 66-15; Table 66-6). Major Compon-
ent of Collection: Ninety-four percent of M. calcarea
occurred in very fine sand to medium silt (4.25-
5.70) with 98 percent of the clams at sediment
sorting values from >1.0 to 2.0 (Table 66-6). Ninety-
seven percent of M. calcarea occurred at depths
from 50 to 100 m (Table 66-7). Minor Component
of Collection: Two percent of the clams occurred in
medium to fine sand (2.0-3.00) and 4 percent in fine
to very fine sand (3.0-4.00) with 1 percent of the
species at sediment sorting values of <.35 and 1 per-
cent at > 0.51-71. Three percent of M. calcarea
occurred at depths of 100-125 m (fine to very fine
sand).
Tellina lutea was present on the nearshore and
central portions of the southeastern shelf and ex-
tending northwest to Nunivak Island (Figs. 66-1,
1168 Benth ic b iology
176°
172'
168°
164°
160°
— I—
156°
Nuculana fossa
Figure 66-10. Distribution oi Nuculana fossa based on collections taken with grab, pipe dredge, clam dredge, and otter trawl.
66-16, and 66-17). The greatest abundance of this
species occurred at Stations 5, 8, 23, and 28 (Figs.
66-16 and 66-17, Table 66-4). The species was
present at 28 percent of the stations sampled by van
Veen grab. The greatest biomass occurred at Stations
5, 7, 9, 22, 23, 25, 41, 59, and 60 (Table 66-4).
Tellina lutea was associated with sediment types
ranging from very coarse to medium silt (—0.77-5.00;
Tables 66-1 and 66-2, Figs. 66-2 to 66-6, 66-16, and
66-17, Table 66-5). Major Component of Collection:
Seventy percent of T. lutea occurred in medium to
fine sand (2.0-3.00) with 83 percent of the clams at
sediment sorting values from 0.35 to 0.5 (39 percent)
and 1.0 to 2.0 (44 percent) (Table 66-6). Seventy-
eight percent of T. lutea occurred at depths from <25
to 50 m (Table 66-7). Minor Component of Collec-
tion: Nine percent of the clams occurred in very
coarse to medium sand (0.0-2.00) and 21 percent in
fine sand to medium silt (3.0-5.00) with 4 percent of
the species at sediment sorting values of <0.35,
12 percent at 0.50-1.0 and 2 percent at 2.0-4.0.
Twenty -two percent of T. lutea occurred at depths of
50-75 m (fine sand to medium silt).
Clinocardium ciliatum was present on the southern,
outer portion of the southeastern shelf and extended
north along the outer portion of the southeastern
TABLE 66-4
Stations of greatest abundance (No./m^ ) and biomass (g/m^ ) of eight species of
bivalves in the southeastern Bering Sea (see Figs. 66-1 and 66-2 for location of stations)
Bivalve species
Nucula tenuis
Nuculana fossa
Yoldia amygdalea
Cyclocardia crebricostata
Clinocardium ciliatum
Spisula polynyma^
Tellina lutea^
Macoma calcarea
28 species
(Table III)
Stations of greatest
abundance (No./m^)
Stations of greatest
biomass (g/m^ )
1,11,12,18,19,28,29,30,63,
71, 72, 82, 83, 935, 937, 939, 942
18,28,29,36,47,49,64,
65,70,71,72
63, 64,70, 70A, 71,72
1,10,11,20,23,55
18, 28,47, 47A, 49
9,25,55,64
5,8,23,28
10, 12, 28, 45, 63, 64, 65, 71, 70A, 83
28, 29, 19, 935, 12, 63, 64, 71, 83
19,28,29,63,71,83,935
29,47,64,71
63,64,70,71,72,83,937
1,6,20,24,55,60
28,29,47
9,55,64
5,7,9,22,23,25,41,59,60
10,22,45,63,64
1,5,9,22,28,41,59,60,
63,64,71
^ Adult Spisula poly ny ma and Tellina lutea were not sampled quantitatively with the van Veen grab. All stations listed here
reflect juvenile clams only.
TABLE 66-5
Percentage of pelecypods collected at each phi
(values based on grab samples)
(based on No./m^ )
Species
.8-<0
0-<l
Phi values
l-<2
2-<3
3-<4
4-<5
5-<6
Nucula tenuis
Nuculana fossa
Yoldia amygdalea
Cyclocardia crebricostata
Clinocardium ciliatum
Spisula polynyma
Tellina lutea
Macoma calcarea
3
40
51
6
12
84
4
1
3
89
7
18
76
1
1
98
1
41
14
45
70
3
18
2
4
94
1169
TABLE 66-6
Percentage of pelecypod species by sediment sorting values based
on soutiieastern Bering Sea grab data 1975
(Based on No./m^)
Species
<0.35
>0.35-0.5
>0.5-0.71
Sorting values
>0.71-1
>l-2
>2-4
>4-10
Nucula tenuis
3
4
0
8
75
10
0
Nuculana fossa
0
0
0
2
96
3
0
Yoldia amygdalea
0
3
0
1
89
7
0
Cyclocardia crebricostata
0
8
13
58
20
1
0
Clinocardium ciliatum
0
0
0
0
100
0
0
Spisula polynyma
5
0
32
1
59
3
0
Tellina lutea
3
39
11
1
44
2
0
Macoma calcarea
1
0
1
0
98
0
0
shelf some distance into the outer shelf (Figs. 66-1,
66-18, and 66-19). The greatest abundance of this
species occurred at Stations 18, 28, 47, 47A, and 49
(Figs. 66-18 and 66-19, Table 66-4). It was present at
21 percent of the stations sampled by van Veen grab.
The greatest biomass occurred at Stations 28, 29, and
47 (Table 66-4). Clinocardium ciliatum was asso-
ciated with sediment types ranging from fine sand to
medium silt (3.4-5.7(^; Tables 66-1 and 66-2; Figs.
66-2 to 66-6, 66-18, and 66-19; Table 66-5). Major
Component of Collection: Ninety-eight percent of C.
ciliatum occurred in very fine sand to medium silt
TABLE 66-7
Percentage of pelecypod species by depth, based on southeastern Bering Sea grab data 1975
(Based on No./m^)
Species
0-25
25-50
Depth!
50-75
5 in percentages
75-100
100-125
125-150
150-175
Nucula tenuis
1
1
52
40
2
4
0
Nuculana fossa
0
0
4
70
24
0
2
Yoldia amygdalea
0
0
28
64
7
0
1
Cyclocardia crebricostata
1
53
46
0
0
0
0
Clinocardium ciliatum
0
0
97
2
1
0
0
Spisula polynyma
1
5
49
45
0
0
0
Tellina lutea
40
38
22
0.
0
0
0
Macoma calcarea
0
1
32
65
2
0
0
1170
I
Bivalve mollusks 1171
Figure 66-11.
1980).
Qualitative distribution of Nuculana fossa taken in the southeastern Bering Sea by van Veen grab (Feder et al.,
(3.4-5.00), with 100 percent of the clams at sediment
sorting values from > 1.0 to 2.0 (Table 66-6). Ninety-
seven percent of C. ciliatum occurred at depths from
50 to 75 m (Table 66-7). Minor Component of
Collection: One percent of the clams occurred in fine
to very fine sand (3.0-4.00) and 1 percent in medium
silt (5.0-5.70). Two percent of C. ciliatum occurred
at depths of 75-100 m and 1 percent at 100-125 m
(medium silt).
Cyclocardia crebricostata was distributed primarily
within Bristol Bay and northwest of the bay, with a
small pocket north of the Pribilof Islands (Figs. 66-1,
66-20, and 66-21). The greatest abundance of this
species occurred at Stations 1, 10, 11, 20, 23, and 55
(Figs. 66-2, 66-20, and 66-21; Table 66-4). The
species was present at 25 percent of the stations
sampled by van Veen grab. The greatest biomass
occurred at Stations 1, 6, 20, 24, 55, and 60 (Table
66-4). Cyclocardia crebricostata was associated with
sediments ranging from very coarse sand to coarse silt
(-0.77-4.80; Tables 66-1 and 66-2, Figs. 66-2 to
66-6, 66-20, and 66-21; Table 66-5). Major Com-
ponent of Collection: Seventy-six percent of C.
crebricostata occurred in fine sand to very fine sand
(3.0-4.00) with 58 percent of the clams at sediment
sorting values from >0.71 to 1.0 (Table 66-6).
Ninety-nine percent of C crebricostata occurred at
depths from 25 to 75 m (Table 66-7). Minor Com-
ponent of Collection: Five percent of the clams
occurred in coarse to medium sand (1.0-2.00),
18 percent in medium to fine sand (2.0-3.00), and
1 percent in coarse sand to medium silt (4.8-5.00)
with 8 percent of the sediment sorting at 0.35-0.50,
13 percent at >0. 50-0. 71, 20 percent at >1.0-2.0,
and 1 percent at > 2.0-4.0. One percent of C. crebrico-
stata occurred at depths of <25 m (coarse sand).
The older and larger Spisula polynyma were not
collected quantitatively by van Veen grab, and all
data discussed below refer to juvenile clams only.
Some quantitative data for S. polynyma are included
in Feder et al. (1980), Hughes (1977), and Hughes
and Bourne, Chapter 67, this volume. Spisula polyn-
yma was distributed over the southeastern Bering Sea,
but mainly on the southeastern part of the southeast-
em shelf. It also occurred southwest of Nunivak
Island, northeast of the Pribilof Islands, and at
1172 Benthic biology
176°
172°
168°
164°
160°
156°
Yoldia amygdalea
62'
60°
58°
56'
54°
Figure 66-12. Distribution of Yoldia amygdalea based on collections taken with a grab, pipe dredge, clam dredge, and otter
trawl.
shallow depths off the Alaska Peninsula and Unimak
Island (Figs. 66-2, 66-22, and 66-23). The greatest
abundance of young of the species occurred at
Stations 9, 55, and 64 (Table 66-4). Spisula polynyma
was associated with sediment types ranging from
medium sand to medium silt (2.0-5.00) (Tables
66-1 and 66-2, Figs. 66-2 to 66-6, 66-22, and 66-23,
Table 66-5). Major Component of Collection:
Fifty-nine percent of S. polynyma occurred in fine
sand to medium silt (3.0-5.00) with 59 percent of the
clams at sediment sorting values from >1.0 to 2.0
(Table 66-6). Ninety -four percent of S. polynyma
occurred at depths from 50 to 100 m (Table 66-7).
Minor Component of Collection: Forty -one percent
of the clams occurred in medium to fine sand (2.0-
3.00) with 5 percent of the species at sorting values
of <0.35, 33 percent at > 0.50-1.0, and 3 percent at
> 2.0-4.0. Seven percent of S. polynyma occurred at
depths of < 25-50 m (medium to fine sand).
Bivalve mollusks (mixed species) were most
numerous at stations on the midportion of the
southeastern shelf (Figs. 66-1, 66-2, and 66-24; Table
66-8); for example, Station 28 had 3,374 clams /m ^ ,
Station 29, 834/m^ ; Station 19, l,770/m2 ; Station
935, 796/m^ ; and Station 12, 482/m2 . Large num-
bers of clams were also found at Stations 63 and 64
Bivalve mollusks 1 173
180'^
175'
170°
165"
160'
155°
175"
170
165"
160"
Figure 66-13. Qualitative distribution of Yoldia amygdalea taken in tiie southeastern Bering Sea by van Veen grab (Feder et
al., 1980).
(554 and 1,380 clams/m^ , respectively) on the outer
shelf and Station 71 (774 clams/m^ ) and Station 83
(574 clams/m^ ) on the central shelf .
Of the 28 species of bivalve mollusks collected in
the southeastern Bering Sea, 12 were found in at least
18 percent of the stations sampled by grab (Feder et
al. 1980): Nucula tenuis (77 percent of the stations
sampled), Axinopsida serricata (56 percent), Thyasira
flexuosa (39 percent), Nuculana fossa (36 percent),
Yoldia scissurata (28 percent), Tellina lutea (28 per-
cent), Cyclocardia crebricostata (25 percent), Yoldia
amygdalea (23 percent), Macoma calcarea (23 per-
cent), Clinocardium ciliatum (21 percent), Spisula
polynyma (20 percent), and Serripes groenlandicus
(18 percent).
Bivalve (mixed species) biomass was generally
greatest at stations on the inshore portion of the
southeastern shelf (Figs. 66-1, 66-2, and 66-25, Table
66-9); for example. Station 5 had 573.1 g/m^ ;
Station 9, 158.4 g/m^ ; Station 22, 87.6 g/m^ ; Sta-
tion 41, 90.1 g/m^ ; Station 60, 72.1 g/m^ ; and Sta-
tion 59, 98.6 g/m^ . Large biomass values were also
noted on the mid-portion of the shelf at Station 28,
2193.3 g/m^ ; Station 63, 89.0 g/m^
65.3 g/m^ and Station 64, 63.3 g/m^ .
DISCUSSION
Station 71,
Although bivalve mollusks and other infaunal
species have patchy distribution, it is often possible
to predict their occurrence on the basis of sediment
particle size, sediment sorting (Sanders 1958, 1960;
Stoker 1973, 1978; Shevtsov 1964), and depth. The
data presented in this section suggest that, in general,
the distribution of the bivalves Nucula tenuis,
Nuculana fossa, Yoldia amygdalea, Cyclocardia
crebricostata, Clinocardium ciliatum, Spisula
polynyma, Tellina lutea, and Macoma calcarea is
associated with specific sediment size, sorting ranges,
percentage of mud, and depth (Table 66-10).
Five of the species of clams examined— Nucu/a
tenuis, Nuculana fossa, Yoldia amygdalea, Tellina
lutea, and Macoma calcarea— 2txe representatives of a
major trophic group, detrital or deposit feeders, in
the Bering Sea (Kuznetsov 1964, Filatova and
Barsanova 1964). These clams are typically found in
1174 Benth ic b io logy
176"
172°
168°
164°
160°
156°
62°
60°
58°
56°
54°
Macoma calcarea
Nushagak Kvichak
Togiak River River River
CS 9^""
Figure 66-14.
trawl.
Distribution of Macoma calcarea based on collections taken with a grab, pipe dredge, clam dredge, and otter
fine sand and coarse silt (Table 66-10). Nucula tenuis,
N. fossa, and Y. amygdalea are primarily deposit
feeders; M. calcarea and T. lutea may also function as
suspension feeders (Filatova and Barsanova 1964,
Kuznetsov 1964). The filter-feeding bivalves Cyclo-
cardia crehricostata, Clinocardium ciliatum, and
Spisula polynyma may also occur in similar sediment
regimes, and the former two species are probably able
to utilize resuspended detrital debris over the water-
sediment interface in such areas (Ho skin et al. 1976,
Hoskin 1977, Mueller et al. 1976).
The organic carbon of marine sediments may be
derived from remote regions (allochthonous), such as
river systems, or produced in the overlying water
column (autochthonous), or both. The quality and
quantity of the organic carbon available to benthic
organisms are related to the distance and source of
allochthonous material, the productivity and carbon
coupling activities in the overlying water column,
suspended load-type of sediment, particle size and
settling rates, and resuspension mechanisms present.
Organic carbon is concentrated in sediments near
Togiak Bay and the outer Bering shelf regions (Figs.
66-1 and 66-7). In these regions, the organic carbon
content of sediments is directly proportional to the
clay content of the sediment (Sharma 1972). It has
Bivalve mollusks 1175
Figure 66-15. Qualitative distribution of Macoma calcarea taken in the southeastern Bering Sea by van Veen grab (Feder et
al. 1980).
been suggested that organic material is generally
transported and deposited with fine silts or clay-sized
sediments. These processes may result from adsorp-
tion of organics on the clay-sized particles or from
current systems which control distribution and
deposition of materials carried in suspension, or both
(Sanders 1958, Sharma 1972, Hoskin 1978, Driscoll
and Brandon 1973). The greater silt, clay, and
organic matter in the outer Bering Sea shelf region
and adjacent areas may partly explain the high
numbers and biomass of bivalves at Stations 55, 63,
64, 65, 71, 72, and 83 northwest of the Pribilof
Islands and south of St. Matthew Island.
There are other factors not considered in this
section that probably influence the distribution of
pelecypods in the southeastern Bering Sea. Further
data are needed to assess their importance. These
include predation (Shubnikov and Lisovenko 1961,
Mineva 1961, Skalkin 1960, Neiman 1964), in-
tensity of circulation in the overlying waters
(Takenouti and Ohtani 1972), concentrations of
suspended material in the overlying water (Sharma et
ai. 1972, Sharma 1972), organic content of the
sediments (Driscoll and Brandon 1973, Franz 1976),
bottom temperature (Neiman 1960, 1964; Semenov
1964), and effectiveness of grazing in the overlying
water column, i.e., efficiency of carbon coupling in
the water column (Alexander and Cooney 1979).
Alexander and Cooney (1979) have suggested that
the carbon system within the water column of the
midportion of the southeastern Bering Sea shelf may
be poorly coupled (Fig. 66-1). The zooplankton here
are apparently unable to graze either the phytoplank-
ton as rapidly as it is produced or the larger species of
diatoms. Consequently, it is assumed that much of
the carbon produced as phytoplankton reaches the
bottom, where it becomes available for suspension-
feeding and deposit-feeding invertebrates. The
presence of dense populations of some species of
bivalve mollusks on the midportions of the south-
eastern Bering Sea shelf (Stations 11, 12, 18, 19, 28,
29, 30) may reflect the periodic fallout of phyto-
plankton in an uncoupled system. Furthermore, the
trophic importance of the mid-shelf region and its
resident clam and other infaunal species is indicated
by the presence of commercial quantities of snow
1176 Benthic biology
176°
172°
168°
164°
160°
156°
Tellina lutea
^ V^^^
I
Figure 66-16. Distribution of Tellina lutea based on collections taken with a grab, pipe dredge, clam dredge, and otter trawl.
crab, king crab, and yellowfin sole that feed on
infauna there (Feder et al. 1978b; Feder et al. 1980;
Feder and Jewett 1980; Pereyra et al. 1976; Otto,
Chapter 61, this volume).
BIVALVE AGE AND GROWTH
Neiman (1964) examined the age composition of
bivalve moUusks in the middle zone of the eastern
Bering Sea shelf and found that a large percentage
of the population consisted of clams between four
and six years old. She hypothesized that the benthos
of the middle shelf was not heavily utilized as food
by higher trophic levels and that such predators as
flatfishes were excluded from the area by the pres-
ence of low water temperatures during the winter. In
May 1976, we collected bivalves in the area from
which the 1961 collections were made in an effort to
extend the information on abundance, age composi-
tion, and growth history. The size and age data and
growth histories of Nucula tenuis, Nuculana fossa,
Yoldia amygdalea, and Macoma calcarea were deter-
mined . Growth information is also presented for two
larger species of clams, Spisula polynyma and Tellina
lutea.
Bivalve mollusks 1 177
59°
56°
53°
180"
175" 170" 165"
160" 155"
-i Tellina lutea
\ S.E. Bering Sea
/ Abundance (N/m^)
/ — 0 < 24
24 < O < 48
48 < O < 72
_ 72<Q
/ 1
ifm^H
59
56°
53"
r
)
i|i
^fi
\
^1
T.^
\
\
^,
M" 11
— e -r
^
\\
-x^y
^
■C^
^
"^
hi] -I
ty
c
h
\
— r?"";^ai
\ {
— X
'^^&^
1 •^MnH-^i>'t4---T
A
100 0 100 200 km
(
r
4$
'£
Pu2
50 0 50 100 miles
Wx^
y-
i/&
p
r —
'^"1 1
^ /
V-
1 1 1 I I I _w-
\-^
175"
170' 165'
160
Figure 66-17.
1980).
METHODS
Qualitative distribution of Tellina lutea taken in the southeastern Bering Sea by van Veen grab (Feder et al.
Clams were collected in May 1976 with a pipe
dredge (100 cm X 35 cm) from the NOAA ship Miller
Freeman, on a grid established for the OCSEAP
benthic infaunal program (Feder et al. 1977, Feder et
al. 1980) (Table 66-11, Fig. 66-26). Sediments were
washed through a screen of 1 mm^ mesh, and
clams were separated from other benthic organisms.
Since this technique probably causes some loss of
fragile young clams, the abundance of early year-
classes may be underestimated. Another collection of
Spisula polynyma was made in July and August 1977
from the F/V Smaragd with a hydraulic clam dredge,
rings 75 mm in diameter in the retaining bag, along
the west side of the Alaska Peninsula (Table 66-11,
Fig. 66-26).
Six common, relatively ubiquitous species were
selected for detailed study: Nucula tenuis, Nuculana
fossa, Yoldia amygdalea, Spisula polynyma, Macoma
calcarea, and Tellina lutea. Clinocardium ciliatum
was common, but severe abrasion of the umbos
prevented accurate aging of the available mate-
rial. Clams selected for age determination came from
stations where the species were most abundant. Age
was determined by the annular method (Weymouth
1923). Annuli, a series of closely spaced concentric
growth rings, are formed during the winter months in
Alaskan waters (Paul and Feder 1973). The term
0-age refers to clams of the settling year-class that
have undergone only one growing season, less than six
months, before forming their first winter annulus.
Thus, clams referred to as 1 year of age are actually
17 or 18 months old and have lived through two
growdng seasons. The 0-age groups in this chapter and
the 1-year groups of Neiman's paper (1964) are
analogous. Neiman's one-year-old clams are recorded
as 0-age clams in this chapter. The 0 annulus was
measured only on 0-age clams, because abrasion of
the umbos of most older shells obliterated this
annulus. Two types of measurements were made on
all shells; total shell length and length at each annulus.
Growth history figures were deduced from the shell
length at each annulus. Since the last annulus on all
specimens was formed in the vdnter months during
overlapping calendar yeeirs, length values for these
1178 Benthic biology
176
62°
60°
58°
56°
54°
172°
168°
164°
160°
156°
Clinocardium ciliatum
Nushagak Kvichak
Togiak River River River
I
""^-,__^,^ y'V^fi^ ^Un/mok Pass
^^>^^
Figure 66-18. Distribution of Clinocardium ciliatum based on collections taken with a grab, pipe dredge, clam dredge,
and otter trawl.
annuli were assigned to the year which includes the
entire growing season. For example, the last annulus
on the specimens from the pipe-dredge collection was
formed during the winter months of 1975-76, and
the last length values were assigned to the growing
year 1975 in the growth history figures.
Mean shell length, range, standard deviation, and
standard error of the mean were plotted to show the
relationship between shell length and age for the six
species of clams. The mean is denoted in the last-
mentioned plot by the horizontal line, the range by
the vertical line, the two standard deviations by the
white box, and the two standard errors of the mean
by the cross-hatched box. The standard deviations
and the standard errors of the mean are not shown
for age-classes with a sample size of 29 or fewer.
Mortality rates for Nucula tenuis, Nuculana fossa,
and Macoma calcarea were determined by the method
of Gruffydd (1974), which assumes that although
recruitment varies from year to year at specific
stations, overall recruitment to a large area is constant
for an unfished population. Thus, the total number
of each species of clam was plotted against age. The
calculated curves eliminate the effect of uneven
Bivalve mollusks 1179
180°
175'
170°
165°
160'
155°
50 100 miles
I I
175
170
165°
160°
Figure 66-19. Qualitative distribution of Clinocardium ciliatum taken in the southeastern Bering Sea by van Veen grab
(Federetal. 1980).
recruitment apparent in individual samples. Using the
number of individuals calculated from the curve
rather than the actual catch, the percent mortality at
each age is estimated. The numbers at age from the
curves are calculated using the expression :
where N = number of clams, z = mortality coefficient,
t = time, t + 1 = time at the next year, and the
constant e = 2.718. The mortality curves were drawn
by a Honeywell 66/40 computer, a modification of
Gruffydd's technique (1974) in which the curves
were plotted by eye on semilog paper.
RESULTS
Growth
Increases in shell length of 0.5-4.0 mm/yr occur in
the small species Nucula tenuis, Nuculana fossa,
Yoldia amygdalea, and Macoma calcarea (Tables
66-12 to 66-15, Figs. 66-27 to 66-30, 66-34 to
66-37), and 0.9-6.2 mm/yr for the larger clams
Spisula poly ny ma (Hughes and Bourne, Chapter 67,
this volume) and Tellina lutea (Tables 66-16 and
66-17, Figs. 66-31 to 66-33, 66-38, and 66-39). The
small clams are relatively long-lived; N. tenuis and N.
fossa reach 9 years of age and 13 and 21 mm in shell
lengths, respectively, Y. amygdalea reach 13 years
and 32 mm, and M. calcarea 11 years and 49 mm
(Figs. 66-34 to 66-37). The larger clams grow at
faster rates and seem to live even longer; S. polynyma
and T. lutea live 14 years and attain 135 and 83 mm
in shell length, respectively (Figs. 66-38 and 66-39).
Hughes and Bourne (Chapter 67, this volume) have
reported a 19-year-old S. polynyma at 123 mm. No
radical differences in size and age within each of the
six species of bivalves examined were observed
relative to their point of collection on the southeastern
Bering Sea shelf (Tables 66-11 to 66-17, Fig. 66-26).
Age composition
The age analyses of those small species of clams
taken by pipe dredge, Nucula tenuis, Nuculana fossa,
Yoldia amygdalea, and Macoma calcarea, show that
these clams are generally long-lived, reaching ages of
1180 Benthic biology
156°
Q> .^^^
Figure 66-20. Distribution of Cyclocardia crebricostata based on collections taken with a grab, pipe dredge, clam dredge, and
otter trawl.
8-13 years (Tables 66-12 to 66-15). The age composi-
tion of a species at different stations was variable.
Furthermore, at stations where a species was abun-
dant, there were several year-classes rather than large
numbers of new recruits. The age composition of
these small infaunal species at the stations examined
is dominated by older clams; however, large numbers
of young N. tenuis occurred at Station 12 (Tables
66-12 to 66-15).
Mortality
Mortality between year-classes for Nucula tenuis,
Nuculana fossa, and Macoma calcarea generally
exceeded 20 percent (Tables 66-18 to 66-20; Figs.
66-40 to 66-42). The year-classes five and six are the
first that are subject to 50-percent mortality (Tables
66-18 to 66-20). Although these species are relatively
long-lived, 44 percent of N. tenuis were less than
three years of age. Eighty percent of N. fossa and
87 percent of Macoma calcarea were less than five
years of age. The mortality estimations for Spisula
polynyma are reported by Hughes and Bourne
(Chapter 67, this volume). The samples of Yoldia
amygdalea and Tellina lutea were not adequate for
mortality estimations.
Bivalve mollusks 1181
Figure 66-21. Qualitative distribution of Cyclocardia crebricosta taken in the southeastern Bering Sea by van Veen grab
(Federetal. 1980).
GENERAL DISCUSSION
The clam age studies presented in Table 66-21
compare the results of Neiman (1964) and Feder et
al. (1980) in the southeastern portion of the Bering
Sea with those of Stoker (1978) in the northern
Bering Sea and the Chukchi Sea. Neiman (1964) and
Feder et al. (1980) report similar sizes at age for
Nucula tenuis, Nuculana fossa, and Macoma calcarea
for agesO through 3 (Table 66-21). Data from
Neiman (1964) for older clams indicate differences of
0.5-5.2 mm in shell lengths greater than the sizes at
age reported by Feder et al. (1980; Table 66-21).
Accurate determinations of true annuli in older clams
are difficult, and the disparities in the two studies are
probably due to differences in aging technique rather
than actual differences in growth rates. Shell lengths
of M. calcarea at a given age in the Chukchi Sea are
2-3 mm shorter (Stoker 1978) than those reported
for the southeastern Bering Sea in Table 66-21.
Growth history data (Figs. 66-27, 66-28, and 66-30)
and previous work by Feder et al. (1980), Neiman
(1964), and Stoker (1978) suggest that growth rates
of these species have not exhibited marked fluctua-
tions from 1961 to 1976 (Table 66-21). Growth
history data for individual stations in the Bering Sea
are reported in Feder et al. (1980).
Since the 0-age Spisula polynyma were collected in
May, they were assumed to have overwintered rather
than to be newly settled clams. Hughes and Bourne
reported (Chapter 67, this volume) that S. polynyma
spawn from late June through early August. The
shell lengths of age 0 ranged from 3.3 to 5.0 mm (Fig.
66-38). There is poor agreement for size at age of 5.
polynyma from ages 0 to 9 between this report and
that of Hughes and Bourne (Chapter 67, this volume;
Feder et al. 1978a), although the sizes reported by
the two studies are similar for clams older than
10 years of age. A field study program is necessary to
accurately describe the growth of this species.
The variation in year-class strengths observed at
different stations for the bivalve species examined in
this study indicates variable annual recruitment
success for any specific location. However, when the
age composition of clams from all examined stations .
1182 Benthic biology
176°
172°
168°
164°
160°
156°
62°
60°
58°
56°
54°
Spisula polynyma
Nushagak Kvichak
Togiak River pjver River
<^\
^~-~--__^ /- /^C^ Jz^Unimok Pass
Figure 66-22. Distribution of Spisula polynyma based on collections taken with a grab, pipe dredge, clam dredge, and otter
trawl.
combined (Tables 66-12 to 66-17) is considered, no
cases of total year-class failure were observed. Cur-
rently, the factors affecting recruitment success in
bivalve populations of the area are unknown. The age
composition of all six species was characterized by
the occurrence of numerous older clams (Tables
66-12 to 66-17). The data for these calculations are
taken primarily from areas where these species are
abundant and predators are rare or absent (Tables
66-11, 66-22, and 66-23, Fig. 66-26). Neiman (1964)
observed a similar age-distribution in the southeastern
Bering Sea (Table 66-21) and suggested that the large
number of older clams indicated that predation was
not a significant factor affecting bivalve densities
there. Since Nuculana fossa, Yoldia amygdalea, and
Macoma calcarea are small species, predators probably
do not discriminate between old and young by size.
The typically low densities of N. fossa, Y. amygdalea.
Bivalve moUusks 1183
180'
175"
170°
165'
160'
155"
160
Figure 66-23. Qualitative distribution of Spisula polynyma taken in the southeastern Bering Sea by van Veen grab (Feder et
al. 1980).
and M. calcarea in the areas where there are large
numbers of crabs and flatfishes (Tables 66-13 to
66-15, 66-22, 66-23, and Figs. 66-11, 66-13, and
66-15) (Pereyra et al. 1976) suggest that mortality
rates in these areas are much higher. The presence of
large numbers of N. tenuis throughout the study area
suggests that this species is not heavily preyed upon
by crabs and flatfishes (Tables 66-11, 66-22, and
66-23; Fig. 66-9). Nuculana and Macoma have been
identified as major prey species of the snow crab
Chionoecetes opilio and king crab Paralithodes
camtschatica in the Bering Sea (Feder et al., 1980),
and of the snow crab C. bairdi and king crab in
Cook Inlet (Feder et al. 1979, Paul et al. 1979).
Tarverdieva (1976) also states that bivalves are an
important prey for all three species of crabs in
the southeastern Bering Sea. The results of the
present survey support Neiman's age-composition
180'
175'
170°
165'
160'
155'
Figure 66-24. Abundance of clams (28 species), southeastern Bering Sea.
analysis. Further study is necessary to quantify the
predator-prey interactions occurring in the Bering
Sea.
In the six species of Bering Sea clams, the variable
recruitment success at individual stations and non-
random distributions make population monitoring
at stations impractical. However, growth rates of the
species examined, as evidenced by growth histories.
have been relatively stable over time. Monitoring
growth and growth histories could be used to detect
changes in the environment capable of affecting rates
of shell formation. The growth history technique
could be used to detect this type of change even after
a change in the environment, such as an oil spill,
because normal growth rates could be determined for
the area by examining growth histories.
1184
TABLE 66-8
Total number of clams/m^ by station on the southeastern Bering Sea shelf
(Table based on data in Feder et al. 1980)
Station
Total No./m^
Station
No./m^
Station
No./m^
1
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
22
23
756
36
20
105
6
6
162
206
52
264
482
93
4
16
56
206
590
1770
52
15
42
25
43
27
14
28
3374
29
834
30
278
31
183
35
26
36
142
37
6
38
46
39
12
40
11
41
15
42
32
43
26
45
664
47
232
49
182
55
186
57
14
TABLE 66-9
59
60
61
62
63
64
65
70
71
72
73
82
83
924
935
937
939
941
942
21
12
8
26
554
1380
446
87
774
250
6
262
574
54
796
426
242
42
91
Total clam biomass (g/m^ ) by station on the southeastern Bering Sea shelf
(Table based on data in Feder et al. 1980)
Station
g/m'
Station
g/m^
Station
g/m'
1
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
22
23
140.96
9.24
0.05
573.14
23.63
61.86
8.71
158.35
57.53
5.99
13.51
4.22
0.07
0.34
0.29
1.35
12.93
101.43
14.49
87.58
74.03
24
25
27
28
29
30
31
35
36
37
38
39
40
41
42
43
45
47
49
55
57
45.61
59
41.14
60
6.18
61
2193.26
62
67.37
63
3.50
64
2.20
65
0.61
70
2.39
71
1.54
72
0.57
73
0.43
82
0.75
83
90.09
924
1.93
935
0.93
937
26.62
939
23.05
941
2.10
942
40.76
0.22
98.55
72.12
7.55
11.61
89.01
63.34
9.76
13.89
65.32
26.15
0.07
18.07
50.08
2.88
11.18
14.12
11.05
5.65
6.69
1185
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180°
175'
170°
165°
160'
155'
175"
170'
165'
160
Figure 66-25. Total clam biomass (28 species), southeastern Bering Sea.
1187
176
Location of stations where the
clam samples were collected by
pipe dredge.
D Location of stations where clam
samples were collected by clam
dredge.
54'
176° I '2° '68° i64
Figure 66-26. Location of stations wiiere pipe-dredge and hydraulic clam-dredge clam samples were collected.
1188
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1189
TABLE 66-12
Age composition and mean siiell lengtli (ML) of Nucula tenuis from stations
12, 18, 19, 30, 38, and 70 in the southeastern Bering Sea
(ML = in mm, N = number of specimens)
Year-
Station
il2
Station 18
Station 19
Station 30
Station 38
Station 70
class
N
ML
N
ML
N
ML
N
ML
N
ML
N
ML
0
96
1.4
0
—
0
—
0
—
5
1.7
1
1.7
1
96
2.2
0
—
1
2.0
7
2.5
6
2.4
11
2.7
2
20
3.3
4
3.7
10
3.7
18
3.6
13
3.4
14
3.5
3
4
4.1
8
4.9
23
4.8
27
4.7
2
4.7
20
4.9
4
17
6.1
6
5.8
2
5.6
0
—
20
6.0
5
6
7.1
10
7.2
1
6.9
0
—
10
7.2
6
13
8.4
12
8.8
0
—
5
8.1
7
6
9.8
23
10.1
0
—
2
9.2
8
10
10.5
1
10.2
9
5
12.3
Totals
216
54
100
55
27
83
TABLE 66-13
Age composition and mean shell length (ML) o( Nuculana fossa from stations
17, 18, 28, 30, 64, A69, 70, A70, and B86 in the southeastern Bering Sea
(ML = in mm, N = Number of specimens)
Year-
Station 17
Station 18
Station 28
Station 30
Station 64
Station A69
Station 70
Station A70
Station B86
class
N
ML
N
ML
N
ML
N
ML
N
ML
N
ML
N
ML
N
ML
N
ML
0
0
—
0
—
0
—
1
2.5
0
—
0
—
0
—
0
—
0
—
1
3
4.2
3
4.3
0
—
1
3.0
15
4.2
1
2.8
9
3.9
4
3.9
1
3.5
2
0
—
1
6.5
12
6.0
5
6.5
10
5.7
6
6.6
3
5.3
3
2
8.3
0
—
40
8.5
3
8.5
26
8.8
2
7.7
2
9.3
4
0
—
0
—
47
10.9
1
10.7
20
10.8
2
10.7
6
10.6
5
1
13.7
2
13.1
6
12.4
19
12.8
2
12.8
6
0
—
5
14.5
1
13.1
8
14.1
2
14.3
7
2
17.3
30
16.9
8
11
18.4
9
6
19.9
Totals
3
8
55
2
121
10
92
18
12
1190
TABLE 66-14
Age composition and mean shell length (ML) of Yoldia amygdalea from
stations 38, 70, and A70 in the southeastern Bering Sea
(ML = in mm, N = number of specimens)
Year-
class
Station 38
N
ML
N
Station 70
ML
N
Station A70
ML
0
1
2
3
4
5
6
7
8
9
10
11
12
13
Totals
11
1
2.0
3.2
12
0
2
3
4
5
4
5
12
6
0
0
2
1
1
45
3.7
5.6
7.6
9.7
11.6
14.4
17.1
19.2
27.7
28.8
32.1
0
—
0
—
1
6.3
0
—
7
10.0
7
12.1
13
14.3
25
16.5
10
18.2
2
20.0
1
23.8
2
27.0
2
28.3
2
72
30.7
TABLE 66-15
Age composition and mean shell length (ml) oiMacoma calcarea from Stations
10, 28, 64, 70, and A70 in the southeastern Bering Sea
ML = in mm, N = number of specimens
Year-
Station 10
Station 28
Station 64
Station 70
Station A70
class
N
ML
N
ML
N
ML
N
ML
N
ML
0
0
—
0
—
0
—
1
2.1
0
—
1
0
—
0
—
0
—
9
3.9
1
3.5
2
0
—
2
7.1
35
4.5
37
5.7
76
6.6
3
0
—
16
9.2
171
6.5
109
7.5
131
8.6
4
0
—
61
11.4
25
8.8
127
9.5
8
12.3
5
0
—
96
12.9
4
11.0
12
12.6
2
14.9
6
0
-
8
15.0
0
—
2
17.8
7
0
—
0
—
0
—
8
0
—
0
-
1
20.7
9
0
—
0
—
1
25.1
10
0
-
0
—
11
0
—
1
48.8
12
1
39.2
13
2
41.5
Totals
3
183
236
299
218
1191
MSL - Mean Shell Length In mm
Figure 66-27. Growth history of Nucula tenuis from six
stations in the eastern Bering Sea.
MSL - Mean Shell Length in mm
Figure 66-28. Growth history of Nuculana fossa from nine
stations in the eastern Bering Sea.
i2
(0
<s
O
!5
4)
>-
•^ (A
s <
eg
(0 3
s <
rt
15 S
IS s
-1 5
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S <
in
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ra 3
si
(0
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IS 3
(A c
00
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at
« s
(A c
0
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n
13§
1
4.%s^
6!4k,
■£2i\
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15.6\
20.7\
25X
\
48^
45
2
3.7*i|
286
3
ai'six
5.7^
281
4
3.6\
5.7\^
8.0\
200
5
3.5>\
5.8\
8.3V
10.4\
110
6
3.3\
5.3\
7.6\
10.4\
12.8\
10
7
\
\
\
\
\
\;
0
8
3.5\
5.l\
8.7\
10.4\
15.3\
17.7\
19.2\
1
9
3.8\
6.0\
8.3\
10.8\
13.8\
16.3\
19.9\
22.4N
1
10
^:
\
\
\
\
\
\
0
11
3-%s.
6.P|
8.9>\
I2!4N|
17 VS.
^!
29.9\
36!r|
40X,
45.S*Si
1
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975
Total
Year of Annulus Formation
935
MSL - Mean Shell Length in mm
Figure 66-29. Growth history of Yoldia amygdalea from
three stations in the eastern Bering Sea.
MSL - Mean Shell Length in mm
Figure 66-30. Growth history of Macoma calcarea from
four stations in the eastern Bering Sea.
1192
(0
(0
(0
O
k.
(0
o
>
MSL at
Annulus 1
MSL at
Annulus 2
MSL at
Annulus 3
Number In
Year Class
1
6.9\
10.2k
16.4K
24
2
5.3\
3
3
\
13.0\
1
1973
1974
1975
Total
Year of Annulus
Formation
28
MSL - Mean Shell Length in mm
Figure 66-31. Growth history of Spisula polynyma from
two pipe-dredge stations in the eastern Bering Sea.
MSL - Mean Shell Length in mm
Figure 66-32. Growth history of Spisula polynyma from
five hydrauUc clam dredge stations in the eastern Bering
Sea.
MSL - Mean Shell Length in mm
Figure 66-33. Growth history of Tellina lutea from six
stations in the eastern Bering Sea.
NUCULA TENUIS
Six Stations
Bering Sea
-^¥
+
Age (in years)
Figure 66-34. The relationship between shell length and
age of Nucula tenuis from six stations in the eastern Bering
Sea. Mean is denoted by the horizontal line, two standard
deviations by the white box, two standard errors of the
mean by the cross-hatched box, and range by the vertical
line.
1193
20
19
1
18
r NUCUI.ANA FOSSA J
Nine Stations f
1^
Bering Sea "y
r
16
-
15
-
14
-
—
13
4
:5-
_ 12
E
E 11
£
1 '°
1 9
■ i
I
\'
8
I
I
7
6
^
}- '
5
1
4
4
f
3
— 1 —
2
1
0
0123456789
Age (in years)
Figure 66-35. The relationship between shell length and
age of Nuculana fossa from nine stations in the eastern
Bering Sea. Mean is denoted by the horizontal line, two
standard deviations by the white box, two standard errors
of the mean by the cross-hatched box, and range by the
vertical line.
20
— K
19
-
18
YOLDIA AMYGDALEA
17
Three Stations
Bering Sea
4
I-
16
-
L
J
IS
-
14
-
13
-
12
E
E 11
a
I 9
-
—
—
8
1
7
6
-^
5
4
3
1
2
1
0
0 1 2
3 4 S 6 7 8 9
Age (in years)
Figure 66-36. The relationship between shell length and
age of Yoldia amygdalea from three stations in the eastern
Bering Sea. Mean is denoted by the horizontal line, two
standard deviations by the white box, two standard errors
of the mean by the cross-hatched box, and range by the
vertical line.
20
19
18
MACOMA CALCAREA
Four Stations
17
Bering Sea
16
-
15
14
-
1
13
-
-ii
5S-
12
.
E
|-
-, L
J
E 11
-
1 9
-
I
A
!9-
8
-
i
■ *~
7
i
1 ^
-'
6
i
r
4
- i
f
3
-
2
-
0 1
I 3 <
A
l 5 (
ja (tn years)
) 7 8 9
150
-
140
SPISULA POLYNYMA
130
Seven Stations
r
, —
120
Bering Sea
, i
i^
v- 1
110
-
f
i4
it
100
-
J
n
fi
J
E 90
E
-
4
P
V
J
B 80
-
-1
1
'
a 70
I 60
-
—
-
50
AV^
40
30
A
y'
20
-
10
I
0
1 1
0 1 2 3 4 5 6 7 8 9 10 1 1 12 13 14 15 16 |
Age (In years)
Figure 66-37. The relationship between shell length and
age of Macoma calcarea from four stations in the eastern
Bering Sea. Mean is denoted by the horizontal line, two
standard deviations by the white box, two standard errors
of the mean by the cross-hatched box, and range by the
vertical line.
Figure 66-38. The relationship between shell length and
age of Spisula polynyma from seven stations in the eastern
Bering Sea. Mean is denoted by the horizontal line, two
standard deviations by the white box, two standard errors
of the mean by the cross-hatched box, and range by the
vertical line.
1194
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TELLINA LUTEA
f ' • —
70
Six Stations
60
Bering Sea
—
—
-
-
-*
-
— '
1 50
-
5 40
m 30
- +-
,+^
■^ 20
: +
10
0
'_ -f—
1 1 1 1 1
0 1 2 3 4 5
6 7 8 9 10 11 12 13 14 15 16
Age (In years)
Figure 66-39. The relationship between shell length and
age of Tellina lutea from six stations in the eastern Bering
Sea. Mean is denoted by the horizontal line, two standard
deviations by the white box, two standard errors of the
mean by the cross-hatched box, and range by the vertical
line.
ISOr
NUCULA TENUIS
ca
«
>
n
a
-i^
O
}-i
3
-^
XJ
O
O
c
E
s
CD
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a
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J
T3
cd
0)
2
CO
C
CO
0)
Etc
0)
^^
3
O
Si
B
3
2
oi
Figure 66-40. Graph of abundance vs. age for Nucula
tenuis in the eastern Bering Sea.
100
NUCULANA FOSSA
y x;
•a
C
3
Xi
Oi
>> c
13 '3
0)
OB
-^
03
c
CO
oc
m
ni
o
eo
a
S
T3
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o
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3
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'c
x:
o
OI
x:
c
o
«
Figure 66-41. Graph of abundance vs. age for Nuculana
fossa in the eastern Bering Sea.
1197
TABLE 66-19
The distribution of Nuculana fossa at each age and the relationship between age and
natural mortality in the southeastern Bering Sea
Age
Number at age
from original
data
Number at age
from curve
Fig. 66-41^
Natural mortality
% from curve
Fig. 66-4P
Mortality
coefficient
1
37
37
75
76
30
16
32
11
6
78
68
54
32
13
6
3
13
21
41
59
54
50
0.1372
0.2305
0.5232
0.9008
0.7732
0.6931
Total
321
'Based on the technique of Gruffydd (1974)
TABLE 66-20
The distribution of Macoma calcarea at each age of year-classes and the relationship between age and natural mortality
in the southeastern Bering Sea
Age
Number at age
from original
data
Number at age
from curve
Fig. 66-42^
Natural mortality
% from curve
Fig. 66-42^
Mortality
coefficient
0
1
2
3
4
5
6
7
8
9
10
11
1
45
286
281
200
110
10
0
1
1
0
1
320
230
145
80
30
0
0
0
0
0
28
37
45
63
0.3302
0.4613
0.5947
0.9808
Total
936
'Based on the technique of Gruffydd (1974).
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TABLE 66-22
Grab counts for southeastern Bering Sea stations wiiere bivalves were
collected for age and growth studies (See Feder et al. 1980)
(Based on No./m^)
Station
Nucula
tenuis
Nuculana
fossa
Yoldia
amygdalea
Spisula
polynyma
Tellina
lutea
Macoma
calcarea
4
5
6
9
10
12
18
19
22
23
25
28
30
38
55
64
A69^
70
A70^
B86^
0
0
0
0
0
0
3
0
8
0
458
0
224
18
556
10
0
0
0
0
0
0
142
14
268
4
28
0
6
2
20
620
0
0
0
0
0
0
0
254
0
0
2
0
0
0
2
0
0
2
0
0
0
36
4
0
0
0
0
2
0
76
2
256
0
0
36
0
2
0
10
0
0
8
0
10
0
0
0
0
16
2
24
0
2
0
66
16
0
0
0
0
0
0
0
364
18
12
12
Totals
1731
680
132
626
156
400
'Pipe dredge stations.
350
300
- 200
9
a
E
a
Z 150-
100
50
MACOMA CALCAREA
Age in years
Figure 66-42. Graph of abundance vs. age for Macoma
calcarea in the eastern Bering Sea.
1200
Bivalve mollusks 1201
TABLE 66-23
Catch of bivalve predators in kglkm fished from the
BLM/OCS baseUne survey, August-October 1975
(Pereyra et al., 1976)
Station
Chionoecetes
bairdi
Chionoecetes
Paralithodes
Limanda
opilio
camtschatica
aspera
0
5-20
25-100
0
<5
0
0
5-20
<25
0
5-20
100-250
2-10
>35
100-250
10-25
>35
25-100
<2
5-20
<25
10-25
0
100-250
0
5-20
25-100
0
0
<25
0
<5
<25
10-25
0
25-100
<2
0
0
25-50
0
25-100
2-10
0
<25
>50
0
<25
<2
0
0
<2
0
<25
10-25
0
<25
10-25
0
<25
4
5
6
9
10
12
18
19
22
23
25
28
30
38
55
64
A69
70
A70
B86
<2
0
0
2-10
<2
10-25
<2
<2
2-10
0
0
2-10
10-25
0
2-10
<2
2-10
2-10
<2
2-10
ACKNOWLEDGMENTS
We thank the following Institute of Marine Science
personnel for assistance during this study: Cydney
Hansen and Robert Sutherland for assistance in
data processing, and Ana Lea Vincent and Rosanne
Lamoreaux for drafting.
This work, Contribution No. 432, Institute of
Marine Science, University of Alaska, Fairbanks, was
supported by the National Oceanic and Atmospheric
Administration Outer Continental Shelf Environ-
mental Assessment Program, through interagency
transfer of funds from the Bureau of Land Manage-
ment, Department of the Interior.
1202 Benthic biology
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Stock Assessment and Life History
of a Newly Discovered Alaska Surf Clam Resource
in the Southeastern Bering Sea
Steven E. Hughes' and Neil Bourne^
' Northwest and Alaska Fisheries Center,
Seattle, Washington
^ Pacific Biological Station, Fisheries and Oceans,
Nanaimo, B.C., Canada
ABSTRACT
A 1977 exploratory survey of subtidal clam resources in the
southeastern Bering Sea revealed extensive concentrations of
Alaska surf clams {Spisula poly ny ma Stimpson) along the
north coast of the Alaska Peninsula. Using east-coast hy-
draulic clam harvesters, 1977 and 1978 stock assessment
surveys delineated a geographically isolated stock with an
estimated exploitable biomass of 329,000 mt ± 52,000 and
potential annual yield of 17,800 mt (maximum sustainable
yield) of whole clams. Production fishing trials at 13 sites in
1978 produced an average catch-per-unit -effort of 815 kg/hr
with a clam harvester 1.84 m wide.
Life-history studies indicated that the species is long-lived
(25), slow growing (K = 0.135), fully recruited to the spawn-
ing population at the age of eight, and subject to low natural
mortality (M = 0.135); it attains maximum cohort biomass at
9.4-13 years. A biological rationale for management meas-
ures is presented.
INTRODUCTION
Broad-range studies, funded by federal and State of
Alaska agencies and eight private companies, were
conducted in 1977-78 to investigate the possibility of
establishing a fishery for the Alaska surf or pink neck
clam {Spisula polynyma Stimpson) in the subtidal
waters of the southeastern Bering Sea.
Exploratory surveys resulted in the discovery of a
resource of S. polynyma distributed over an area of
6,800 km^ on the continental shelf near the north
coast of the Alaska Peninsula. Reports have described
fishing gear, general distribution, harvesting feasibility,
preliminary estimates of abundance, and meat quality
(Hughes et al. 1978, Hughes and Nelson 1979). The
surveys and this study also aimed to ascertain the life
history of S. polynyma and to assess the resource in
detail for management purposes. Results repre-
sent the first detailed study of the species in its
1205
predominantly subtidal habitat, although it is known
to have a circumpolar distribution and to occur
near the heavily harvested Atlantic surf clam {S.
solidissima) resources in the north Atlantic.
It seems likely that a fishery for the Alaska surf
clam will be established; consequently it is desirable
(and somewhat unusual) to have baseline biological
data available for managing the resource before it is
harvested commercially.
MATERIALS AND METHODS
Field operations were conducted from the 29-m
fishing vessel Smaragd (750 hp) in 1977 and the 30-m
fishing vessel Sea Hawk (650 hp) in 1978. Survey
gear in 1977 consisted of a 6,000-kg east-coast,
hydraulic-jet clam harvester with 0.9 m knife (fishing
width). The 1978 harvester was lighter (3,000 kg)
and equipped with a 1.8-m knife. Water was supplied
to the harvesters' jet manifolds through a hose 15 cm
in diameter from a 3,000-gal/min pump (1977)
and 4,000-gal/min pump (1978) driven by a 350-hp,
deck-mounted diesel engine. The harvesters were set
and retrieved by trawl winches and towed behind the
vessel with polypropylene line 7.5 cm in diameter
(Hughes et al. 1978, Hughes and Nelson 1979).
Survey design
Three types of survey operations were conducted:
exploratory fishing, resource assessment, and produc-
tion fishing. Initial exploratory fishing and the first
resource-assessment survey were completed during a
1206 Benthic biology
32-day period in July-August 1977. The second
resource-assessment survey and production fish-
ing studies were completed during a 38-day period in
July and August 1978.
The exploratory fishing survey was designed to
find general areas of clam concentration and covered
a wide geographic area at low sampling density.
Accordingly, 106 tows, each lasting 15-30 minutes,
were completed over an area of 20,000 km^ in the
southeastern Bering Sea (Fig. 67-1, Blocks 1-66).
Resource-assessment surveys in 1977 and 1978 were
designed to determine geographic and bathymetric
distribution and abundance of S. polynyma in areas
where concentrations were detected during the
exploratory survey. A total of 365 tows of 10-15
minutes' duration at random sites were completed
along the north coast of the Alaska Peninsula in
survey blocks 40-66 (Fig. 67-1), which collectively
comprise an area of 6,800 km^ . Thirteen areas of high
clam density encountered during the assessment
surveys were fished intensively to determine commer-
cial production catch rates. During this operation,
254 tows of 10-30 minutes' duration were completed.
Catch sampling
Standard deck sampling procedures (Hughes 1976)
were employed to determine species catch composi-
tion, catch rates, size composition, age composition,
and maturity. Shell-length-frequency measurements
(nearest millimeter) were randomly collected from
each 1977 resource-assessment tow and at each 1978
production-fishing site; the desired sample size was
300 clams. Two 1977 and two 1978 independent
stratified samples of S. polynyma shells (25 clams /5
mm length interval) were collected for age analysis,
and one 1977 stratified sample of whole animals (10
clams/5 mm length interval) was collected to deter-
mine the shell length/round weight relationship.
Figure 67-1. Numbered survey blocks in the southeastern Bering Sea where surveys of the Alaska surf clam (S. polynyma)
were completed. Initial explorations were conducted in each block; the 1977 and 1978 resource- assessment surveys were
conducted within blocks 40-66 along the north coast of the Alaskan Peninsula, production fishing studies in 1978 at the 13
dotted locations within survey blocks. Each survey block represents 343 km^.
New Alaska surf clam resource 1207
Gonads collected in 1977-78 for stage-of-
development studies (5 clams/5 mm length inter-
val) were cross-sectioned and fixed in the field with
modified Davidson's Fixative (formalin: 95 percent
ethanol: glacial acetic acid: distilled water; 2:1:3).
In the laboratory, gonads were washed in 5-percent
ethanol, dehydrated, and blocked in paraffin, sec-
tioned at 6-10 microns, and stained with Harris
Modified Hematoxylin and Eosin (H -I- E).
Data analysis
Shell-length-frequency distributions determined
from the 1977 resource-assessment survey were
weighted by catch magnitude and area within survey
blocks; length data collected during the 1978 produc-
tion fishing studies were weighted only by catch
magnitudes.
Growth was determined by measuring shell length
at each annulus after the method of measuring age
and growth in bivalves described by Weymouth et al.
(1925) and discussed by Wilbur and Owens (1964).
Measurements were made with calipers to the nearest
millimeter; length was the straight-line distance
between the margins of an annulus. Use of this
method to determine age and growth depends on
whether annuli are formed and whether they can be
distinguished on the surface of the shell. Surf clams
from the Bering Sea usually have distinct annuli;
those with indistinct annuli (less than 5 percent of
the sample) were discarded. Annuli up to about age
14 were distinct and easily read, but beyond age 14
they tended to be more obscure. Measurements of S.
polynyma past this age cannot be considered as
precise as those of younger clams.
Mean observed (total) shell-length-at-age data
obtained from the two 1977 and two 1978 stratified
shell samples were compared for within-year varia-
tions and, since differences were insignificant, subse-
quently combined into one 1977 and one 1978
age-length key. Resulting proportions of observed
ages at each length were applied to respective 1977
and 1978 weighted length frequencies. For this we
used a computer program by Allen (1966) modified
to exclude extrapolations beyond the age-length
range and to include the calculation of mean length-
at-age as well as numbers-at-age. This analysis pro-
vided weighted age-composition data and mean
length-at-age data for growth studies.
Von Bertalanffy growth-in-length parameters were
determined from the above observed age-length data
and separately from 1977 and 1978 age -length
data obtained from back-measured age rings. Both
techniques have been used in past studies, but they
do not appear to have been compared from a given
sample. Although back-measured age-length data are
of limited value to management since year-classes are
not distinguished, we considered it of scientific
interest to compare growth parameters resulting from
the observed and back-measured age-length data sets.
An area-swept technique (Alverson and Pereyra
1969) was employed to estimate exploitable biomass
using the relationship
P^ = (CPUE)(A)/ca,
where P^ is equal to the average standing stock in
weight of the catchable population, CPUE is catch
per standard unit of effort, A is the total area, a is the
bottom area covered by the clam harvester, and c is a
coefficient related to the effectiveness of the har-
vester in capturing S. polynyma. In this study, c was
assumed to equal one (100-percent efficiency). Al-
though c is undoubtedly less than one, the true value
is unknown, and hence biomass estimates are prob-
ably conservative.
Stock yield was obtained from the relationship
MSY = 0.4 M P^
where MSY is the maximum sustainable yield, M is
the instantaneous mortality coefficient, and P^ is
the estimated exploitable biomass (Alverson and
Pereyra, 1969).
All data are stored at the computer facility. North-
west and Alaska Fisheries Center, NMFS, Seattle,
Washington.
RESULTS
Stock description
The initial exploratory survey indicated no S.
polynyma or extremely low concentrations in the
offshore southeastern Bering Sea, blocks 1-39 (Fig.
67-1) but a potential resource along the north coast
of the Alaska Peninsula between Port Moller and
Ugashik Bay. Ensuing resource-assessment surveys in
1977 and 1978 delineated a S. polynyma resource
throughout survey blocks 40-65, an area of 6,800
km^ . Concentrations were not found southwest of
Port Moller or northeast of Ugashik Bay, perhaps
because of reduced salinities in those areas. Within
the resource area, S. polynyma was most dense at
depths of 30-32 m (Fig. 67-2). The resource appears
to be an isolated stock unit because of unfavorably
low salinities at the northern and southern extremes,
excessive depths in a western direction, and the
landmass of the Alaska Peninsula to the east. Fur-
thermore, a free genetic exchange within that area
seems apparent from the massive spawning activity
which occurred throughout the stock's geographic
1208 Benthic biology
30-1
20-
10-
22-24 26-28 30-32 34-36
Depth (meters)
38-40
42-44
Figure 67-2. Depth-dependent density distribution of tiie
S. polynyma stock off the north coast of the Alaska Penin-
sula as determined during the 1977 resource assessment
survey using a hydraulic clam harvester 0.92 m wide.
-I r
70-74 80-84 90-94 100-104 110-114 120 124 130-134 140-144
Length (mm, by 5-mm increments)
Figure 67-3. Weighted shell-length size-composition of
the S. polynyma stock off the north coast of the Alaska
Peninsula, 1977.
distribution during July and early August 1977 and
1978.
Size, age, and sexual maturity
Size, age, and maturity composition of the stock
were assessed during the initial resource-assessment
survey in 1977. That assessment was conducted
within an area of 5,440 km^ representing 70 percent
of the area occupied by the stock. Shell-length
size compositions of 10,318 animals measured during
that survey were weighted by catch magnitude and
area within sampling blocks to determine a weighted
size composition of the stock (Fig. 67-3). Weighted
age composition (Fig. 67-4) was determined from the
1977 age-length key and the weighted shell-length
composition presented above.
All S. polynyma examined were dioecious. Males
and females collected in July and August 1977 and
1978 were ripe, spawning, or recently spent. Some
male and female animals as young as five years of age
(mean shell length 63 mm) were found to be sexually
active but represented only 10 percent of that age-
group. All eight-year-old clams (mean shell length 83
mm) were sexually active; this was the youngest
age-group fully recruited to the spawning population.
Length-weight relationship and meat yield
Length-weight data for males and females com-
15-
10-
5-
t t t
I I — I — r
4 6
I ' I
10
111
12
I ■ 1 I I
14 16
I
20
Age (years)
Figure 67-4. Weighted age-composition of the S. poly-
nyma stock off the north coast of the Alaska Peninsula,
1977.
bined were determined from 184 animals collected
during the 1977 resource-assessment survey. The
length-weight relationship of clams 30-146 mm long,
determined by fitting the logarithmic form of the
equation W = gL^ when W is whole body weight in
grams and L is shell length in millimeters, is shown in
Fig. 67-5.
Yield of edible meat was determined by hand
shucking 100 kg of fresh S. polynyma and weighing
the meat and liquid fractions. Total whole meats and
liquid weighed 55 kg, drained whole meats 37 kg,
and drained eviscerated meats 29 kg.
New Alaska surf clam resource 1209
Estimates of standing stock
Exploitable biomass estimates were calculated by
survey block for the 1977 and 1978 resource-
assessment surveys and for the two combined (Table
67-1). Although most survey blocks were assessed
each year, work was not completed in blocks 44, 46,
and 56 in 1977 nor in 40, 46, 54, 55, 58, and 61
in 1978. Thus the 1977-78 combined surveys pro-
vided coverage of all blocks occupied by the resource,
40-65, but because of these differences in geographic
coverage total biomass estimates for 1977 and 1978
are not directly comparable. We believe the com-
bined 1977-78 survey data provide the most accurate
estimate of the described S. polynyma exploitable
stock, 329,179 mt ± 52,000 mt of whole clams
(95-percent confidence level).
Production tests
Production fishing tests were completed in 1978 at
13 sites along the north coast of the Alaska Peninsula
(Fig. 67-1) to assist industry and management's
evaluation of potential for a future commercial
fishery. Table 67-2 summarizes catch-effort data and
mean shell length of S. polynyma obtained at each
production site. Weighted size and age composition
of combined catches at all production sites (Fig.
67-6) represent the distribution of size and age
expected in commercial harvests of the resource.
450
400
350
300 -
250
200
150 -
100
50 -
40 50 60 70 SO 90 100 110 120 130 140 150
Shell length (mm)
Figure 67-5. Shell-length/round weight relationship of S.
polynyma off the north coast of the Alaska Peninsula,
1977.
-
.. /
/■
.':■/■
Alaska Surf Clam
i 7'
Antilog intercept = 0.000103
Slope = 3.0583
Sample size = 184
V
"X?""
\ yf
V
i^""
1
Growth
Length-at-age data from the 1977 and 1978
surveys were fitted by the Von Bertalanffy relation
't ^ ^oo (1-e" (^'^0 ^ ), with computational procedures
by Fabens (1965).
15
10-
5 -
t t
10 12
Age (years)
14
I I
1£
15 -|
10
5-
Spisula polynyma
Mean shell length 1 13 mi
N= 9676
T 1 r
70-74 80-84 90 94 100 104 110114 120 124 130 134 140 144
Shell Length (mm)
Figure 67-6. (a) Weighted shell-length size-composition
and (b) weighted age-composition of S. polynyma catches
at 13 production fishing sites along the north coast of the
Alaska Peninsula, 1978. Data represent the projected size-
and age-composition of landings using a hydraulic clam
harvester equipped with a collecting bag with a ring-
diameter of 5 cm.
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New Alaska surf clam resource 1211
TABLE 67-2
Catch rates and mean shell-length size-composition oi Spisula polynyma at 13 production fishing sites along the north coast of
the Alaska Peninsula, 1978. Fishing was conducted with a hydraulic clam harvester 1.84 m wide equipped with a
5-cm ring collecting bag
Production
Survey
Fishing
Total
Catch/Hour
Mean shell length
site no.
block no.
effort (h)
catch (kg)
kg
bu
mm
1
44
1.67
686
411
11.3
124
2
45
1.40
855
611
16.8
124
3
50
2.47
1,667
675
18.6
107
4
57
11.08
8,100
731
20.1
103
5
57
2.60
2,326
894
24.6
111
6
57
9.15
7,327
801
22.0
119
7
56
1.83
1,592
870
23.9
112
8
57
1.67
2,154
1,290
35.5
117
9
59
1.50
1,379
919
25.3
123
10
59
13.05
8,289
635
17.5
112
11
60
1.02
725
711
19.6
120
12
60
2.53
2,297
907
25.0
123
13
62
2.17
2,485
1,147
31.5
108
All sites
52.14
39,882
Mean 815
22.2
Mean 113
Growth patterns and parameters were determined
from means of the observed length s-at-age obtained
from the composite year-classes represented and
separately from mean lengths-at-age determined from
back-measured growth rings. Thus, growth from the
composite year -classes comprising the 1977 and
1978 stock was compared with the generalized
growth pattern which has persisted over the past 19
years. It is not recommended that growth parameters
resulting from back-measured age rings be used
directly for management, but this comparison pro-
vides valuable insight into growth patterns over past
years when no data are available.
Because variation in age-range affects compara-
bility of parameters (Hirschhom 1974) and growth
rings were difficult to read beyond 19 years of
age, curve fits were computed both with fits over a
standardized age-range of 3-19 and with an artificial
data point (0.0) added on the assumption that at
age 0, length is near 0 (Alverson and Carney 1975).
Age increments by the fraction of a year between
mid-dates of spawning (July) and age-ring formation
(January) were assigned to data from back-measured
age rings; no adjustment was assigned to the observed
length -at -age data due to a July sampling date.
Table 67-3 summarizes observed and back-measured
mean lengths-at-age from the 1977 and 1978 surveys
and respective growth parameters. Growth curves
showing departures from the fit are presented for the
1977 and 1978 observed (Fig. 67-7) and back-
measured (Fig. 67-8) data.
Growth patterns and parameters from the 1977
and 1978 observed mean lengths-at-age data indicated
good agreement between years and a stable growth
Age (years)
Figure 67-7. Observed mean length-at-age with fitted
growth curves of stock of Alaska surf clams (S. polynyma)
taken off the north coast of the Alaska Peninsula, 1977-
78.
1212 Benthic biology
TABLE 67-3
Mean shell length (mm) at age and growth parameters (L^^, K, to ) with standard deviations (a) of departures from fit of
Spisula polynyma from the north coast of the Alaska Peninsula; 1977-78 observed are based upon mean length-at-age when
collected and 1977-78 back-measured are based upon age-ring back measurements.
Age
Observed
Age
Back-measured
Item
(Yrs)
1977
1978
(Yrs)
1977
1978
Mean shell
1
—
—
0.5
8.61
7.95
Length-at-age (MM)
2
—
—
1.5
20.03
19.50
3
48.36
42.33
2.5
33.57
32.99
4
51.60
59.28
3.5
45.71
45.90
5
63.18
63.05
4.5
57.47
57.62
6
75.24
74.21
5.5
67.40
67.77
7
89.30
81.89
6.5
75.82
76.49
8
89.64
91.52
7.5
82.95
83.83
9
91.24
92.74
8.5
88.97
89.72
10
97.64
96.72
9.5
94.36
95.03
11
100.80
101.62
10.5
98.96
100.09
12
104.19
105.37
11.5
103.17
104.43
13
109.32
109.50
12.5
106.89
108.22
14
111.46
115.80
13.5
109.94
111.59
15
115.14
116.73
14.5
112.86
114.12
16
115.59
116.34
15.5
115.37
116.25
17
118.51
120.87
16.5
117.62
119.78
18
123.03
125.89
17.5
120.72
122.22
19
128.65
123.38
18.5
122.45
123.00
Parameter
Loo
133.73
134.78
140.30
141.57
sets for
K
-.14
-.13
-.11
-.11
ages 0, 3-19
t„
+.22
-.08
-.10
-.15
a
4.05
2.27
1.375
1.77
Age (years)
Figure 67-8. Back-measured mean length-at-age with
fitted growth curves of stock of Alaska surf clams (S.
polynyma) taken off the north coast of the Alaska Penin-
sula, 1977-78.
pattern. Data indicated that the stock growth com-
pletion rate (K) equals 0.135. Growth patterns and
parameters based upon back-measured age rings
indicate strong stability over the past 19 years and a
slightly slower average growth completion rate (K =
0.11) than noted in 1977 and 1978.
On the basis of the 1977 and 1978 growth equa-
tions from observed length-at-age data and the as-
sumption that the instantaneous mortality coeffi-
cient (M) equals the growth completion rate (K),
maximum biomass production of the stock occurs
between 9.4 and 13 years of age or between 98 and
110.1 mm in length.
Mortality and stock yield
For management purposes, natural mortality rate
(M) is needed to determine yield from stock biomass.
The instantaneous mortality coefficient of the virgin
S. polynyma stock (M = Z) was calculated, with
Alverson and Carney's (1975) assumptions that M
equals the growth completion rate K. Based upon the
New Alaska surf clam resource 1213
1977 and 1978 observed length-at-age growth param-
eters, K equals 0.14 and 0.13, respectively, indicating
a mean M of 0.135.
Independently, we also calculated M from age*
composition data by applying the Heinke technique
to year-classes fully recruited to the sampling gear.
As previously indicated, sampling gear deployed in
1977 was equipped with a collecting bag with a
ring-diameter of 7.6 cm; in 1978 the bag had a ring-
diameter of 5.0 cm. Consequently, it appeared from
respective sets of age-composition data (Figs. 67-4
and 67-6) that 11 was the youngest age fully re-
cruited to the sampling gear in 1977 and age 10 in
1978. Accordingly, for 1977 ages 11-19, M equals
0.12, and for 1978 ages 10-19, M equals 0.16.
The Heinke analysis also indicated that M increases
with increasing age beyond 14; thus expected values
of M representing only that portion of the stock
recruited to the sampling gear would probably be
higher than M = K derived values which apply to the
1-19 life span. Accordingly, 0.135 seems to represent
a realistic value of M.
Potential yield of the described virgin stock of S.
polynyma was obtained from the relationship
MSY = 0.4 M P^
where MSY is the maximum sustainable yield, M is
the instantaneous mortality coefficient, and Pw is the
estimated standing stock or exploitable biomass
(Alverson and Pereyra 1969).
With the 1977-78 exploitable biomass estimate of
P^ = 329,179 mt (Table 67-2) and M = 0.135, MSY
equals 17,775 mt of whole clams. Maximum
sustainable yield may also be expressed as 6,577 tons
of drained whole meats or 5,155 tons of drained
eviscerated meats based upon our reported measure-
ments of meat yield.
SUMMARY AND CONCLUSIONS
A geographically isolated, discrete stock of Alaska
surf clam (S. polynyma) has been described with a
conservatively estimated exploitable biomass of
329,170 mt ± 52,000 mt and potential annual
yield equal to 17,775 tons (MSY) of whole clams.
The species is long-lived (maximum observed age 25),
slow growing (K = 0.135), is fully recruited to the
spawning population at eight years of age, has a low
natural mortality rate (M = 0.135), and attains
maximum cohort biomass at 9.4-13 years of age.
Mortality increases rapidly with increasing age be-
yond 14 and presently the stock appears to be in a
state of equilibrium, probably because it is not fished.
Age-composition data suggest that 11-year-old clams
are the youngest age-group fully recruited to harvest
gear equipped with collecting bags with rings 7.6 cm
in diameter, and 90 percent of catches obtained with
this gear consists of 11- to 19-year-olds. The use of
rings 5.0 cm in diameter in the collecting bags lowers
the age at full recruitment to the geeir to 10 years,
and 85 percent of those catches consists of 10- to
19-year-olds.
In view of the sizable potential yield of the stock
and production catch rates which averaged 736 kg of
clams per hour with a harvester 1.8 m wide, a clam
fishery off the north coast of the Alaska Peninsula is
likely to develop in the near future. Development
may be more rapid because of recent substantial
reductions in the fishery for Atlantic surf clams (S.
solidissima).
Results of life-history studies coupled with recent
declines of Atlantic surf clam stocks indicated that
conservative harvest levels should be maintained on
the described Alaska stock for three to five years to
monitor changes in biological parameters resulting
from fishery pressures. However, because mortality
rates increase rapidly in year-classes beyond 14 years
of age and maximum biomass production per recruit
occurs at 9.4-13 years of age, harvesters should be
equipped with bags with rings 5.0 cm in diameter.
This practice would target the fishery on year-classes
before the increased age of natural mortality and
would increase the stock's biomass per recruit while
allowing a least two seasons of full spawning activity
before subjection to the fishery.
A major deficiency of the reported study is the
lack of knowledge regarding recruitment rates.
Estimates of MSY assume constant recruitment,
which may not apply to this stock; highly variable
recruitment is often characteristic of sedentary
shellfish stocks. Long-term studies to determine
recruitment rates and their variability would be a
major asset to managers in determining more precise
MSY estimates of longer range.
ACKNOWLEDGMENTS
The authors are indebted to Dr. Albert K. Sparks
and Ms. Jolly Hibbits, NMFS, Mukilteo Biological
Laboratory, for their determinations of gonadal
development, and to Mr. George Hirschhorn, NMFS,
Seattle, Washington, for valuable assistance in the
growth studies.
1214 Benthic biology
REFERENCES
Allen, K. R.
1966
Determinations of age distribution
from age-length keys and length dis-
tributions. IBM 7090, 7094, Fortran
IV. Amer. Fish. Soc. 95:230-1.
Alverson, D. L., and M. L. Carney
1975 A graphic review of growth and decay
of population cohorts. J. Conseil
36:133-43.
Hughes, S. E.
1976
System for sampling large trawl
catches of research vessels. J. Fish.
Res. Bd. Can. 33:833-9.
Hughes, S. E., and R. W. Nelson
1979 Trial catches confirm feasibility of
Bering Sea clam fishery. Nat. Fisher-
man, Yearbook Issue 59:36-9.
Alverson, D. L., and W. T. Pereyra
1969 Demersal fish explorations in the
northeastern Pacific Ocean— an evalu-
ation of exploratory fishing methods
and analytical approaches to stock
assessment and yield forecasts. J.
Fish. Res. Bd. Can. 26:1985-2001.
Hughes, S. E., R. W. Nelson, and R. Nelson
1978 Alaskan resource may fill east coast
"clam gap." Nat. Fisherman, Year-
book Issue 58:160-3.
Fabens, A. J.
1965
Properties and fitting of the Von
Bertalanffy growth curve. Growth
29:265-89.
Hirschhom, G.
1974 The effect of different age ranges on
estimated Bertalanffy growth para-
meters in three fishes and one mollusk
of the north-eastern Pacific Ocean.
In: The aging of fish, T. B. Bagenal,
ed., Irwin Bros., Ltd., The Gresham
Press, Old Woking, Surrey, U.K.
Weymouth, F. W., H. C. McMillin, and H. B. Holmes
1925 Growth and age at maturity of the
Pacific razor clam, Siliqua patula
Dixon. Bull. U.S. Bur. Fish. 41:201-
36.
Wilbur, K. W., and G. Owens
1964 Growth. In: Physiology of moUusca,
K. W. Wilbur and C. M. Yonge, eds.,
211-42. Academic Press, N. Y.
Large Marine Gastropods of the Eastern Bering Sea
Richard A. Macintosh^ and David A. Somerton^
' National Marine Fisheries Service
Kodiak, Alaska
^ Center for Quantitative Science,
University of Washington, Seattle
ABSTRACT
Gastropods make up 6-9 percent by weight of the inverte-
brates caught on the continental shelf and upper slope of the
eastern Bering Sea by research trawl surveys. Five species of
the genus Neptunea—N. lyrata, N. pribiloffensis, N. heros, N.
ventricosa, and N. borea/(s— make up 87 percent of the snail
biomass and 68 percent of the snail numbers.
Fifteen of the most common large gastropods were grouped
according to the similarity of environmental variables meas-
ured at the sampling sites at which each species was found.
The variables used were annual maximum bottom temperature
and maximum rate of warming. The analysis identified three
thermal regions in the eastern Bering Sea in late summer, each
region having a distinct assemblage of large gastropod moUusks.
Neptunea spawn over a protracted period and capsular life
of embryos is probably more than six months. Female N.
heros, N. lyrata, N. pribiloffensis, and N. ventricosa mature at
shell lengths of 110, 110, 105, and 102 mm, respectively;
males mature at shell lengths of 95, 100, 90, and 87 mm,
respectively. Recent studies of Neptunea food habits show
that a variety of organisms are consumed, including poly-
chaetes, bivalves, barnacles, fishes, and crustaceans.
Japan has harvested gastropods in the eastern Bering Sea
since at least 1971. Reported catch rates range from 0.9 to
4.0 kg/pot, and total Japanese catch has varied from 404 to
3,574 mt of edible meat per year. The United States has the
capacity to enter the fishery but will probably not do so until
snail products increase greatly in value.
abundant are members of the genus Neptunea, of
which one species or another occurs commonly over
the entire upper continental slope and shelf.
Eastern Bering Sea snails were rarely studied before
Japan started a commercial fishery in the early 1970's.
McLaughlin (1963) outlined the distribution of
invertebrates, including snails, taken north of the
Alaska Peninsula, but subsequent United States
research surveys generally ignored snails. In 1975,
National Marine Fisheries Service (NMFS) trawl
surveys began including an analysis of the distribution
and relative abundance of various snail species in the
eastern Bering Sea.
The Japanese Fishery Agency began research on
the eastern Bering Sea snail resource in 1973. Nagai
(1974) conducted research aboard a commercial
snail pot vessel, and subsequent work has been based
on pot and trawl surveys (Nagai, 1975a, 1975b; Nagai
and Suda 1976; Nagai and Arakawa 1978). Neiman
(1963) described eastern Bering Sea benthic assem-
blages but based her studies on bottom grab samples
that probably do not adequately represent larger epi-
faunal animals such as snails.
During the summers of 1975 and 1976, the North-
west and Alaska Fisheries Center of NMFS conducted
Large marine gastropods are a conspicuous element comprehensive trawl surveys covering approximately
of the eastern Bering Sea macrobenthos. Especially 566,000 km^ of the eastern Bering Sea shelf and
1215
INTRODUCTION
1216 Benthic biology
upper slope (Fig. 68-1). These surveys were designed
to determine what demersal fish and shellfish com-
munities of the eastern Bering Sea could be affected
by development of continental shelf energy resources.
Data on fish and epibenthic invertebrates were
gathered from several hundred locations with a
modified 400-mesh Eastern otter trawl. The data
resulting from these surveys offer significant insight
into the population and biological characteristics of
numerous species of snails. This chapter brings
together information on distribution, species associa-
tion, biology, and the fishery for eastern Bering Sea
snails based primarily on data collected on NMFS
trawl surveys.
SNAIL RESOURCE
Seventy-two species of gastropods in 19 families
were identified in U.S. trawl surveys conducted in
1975 and 1976 (Feder et al. 1978; Pereyra et al.
1976; unpublished data. Table 68-1). While most
small species were usually found inside shells or other
objects, snails larger than about 60 mm in total
length were regularly retained by the trawl mesh.
The small codend mesh size (32 mm) and the bottom-
tending properties of the net allowed a reasonable
assessment of epibenthic snails larger than about 60
mm. How many of these larger snaUs avoid capture
170° 175° 180° 175° 170° 166° 160° 155°
B. POL ARE
Figure 68-1. Station locations and distribution of fifteen large eastern Bering Sea snails.
C. MAGNA
1217
170° 175° 160° 175° 170° 166° 160° 155° 150'
1218
Large marine gastropods 1219
by burrowing into the substrate is not known; esti-
mates of abundance based on trawl surveys will
always be conservative.
Gastropods comprised 1.7 percent of the total
estimated biomass and 6.6 percent of the invertebrate
biomass in the eastern Bering Sea during the 1975
survey (Pereyra et al. 1976). These figures are similar
to the results of the 1978 NMFS trawl survey con-
ducted in roughly the same area, in which snails
made up 2.2 percent of the total biomass and 8.7
percent of the invertebrate biomass (unpublished
data).
Many of the species and most of the snail biomass
in the eastern Bering Sea are attributed to the family
Neptuneidae. Of 67 snail species caught during the
1975 and 1976 surveys, 33 were neptunids. Five
members of the genus Neptunea, N. lyrata, N. prib-
iloffensis, N. heros, N. uentricosa, and N. borealis,
comprised 87 percent by weight and 68 percent by
number of the 1978 catch.
TABLE 68-1
Gastropods identified from 1975 and 1976 NMFS
trawl surveys in tiie eastern Bering Sea. Species
followed by an asterisk (*) are the most commonly
encountered large (>60mm) snails.
Class Gastropoda
Family Trochidae
Margarites giganteus (Leche)
M. costalis (Gould)
Solariella obscura (Couthouy)
S. micraulax
S. varicosa (Mighels and Adams)
Family Turritellidae
Tachyrhynchus erosus (Couthouy)
Family Epitoniidae
Epitonium groenlandicum (Perry)
Family Calyptraeidae
Crepidula grandis Middendorff
Family Trichotropidae
Trichotropis insignis Middendorff
T. kroyeri Philippi
Family Naticidae
Natica clausa (Broderip and Sowerby)
Polinices pallida (Broderip and Sowerby)
Family Velutinidae
Velutina velutina (Muller)
V. lanigera MoUer
V. plicatilis (Muller)
Family Cymatiidae
Fusitriton oregonensis Redfield*
Family Muricidae
Boreotrophon clathratus (Linnaeus)
B.pacificus (Dall)
B. dalli (Kobelt)
Family Buccinidae
Buccinum angulosum Gray*
B. scalariforme (Moller)
B. glaciale Linnaeus
B. solenum (Dall)
B. polare Gray*
B. plectrum Stimpson*
B. rondium Dall
Family Neptuneidae
Clinopegma eucosmia (Dall)
C. magna Dall*
C. ochotensis
Beringius kennicotti (Dall)
B. beringii (Middendorff)*
B. stimpsoni (Gould)
B. frielei (Middendorff)
B. crebricostatus undatus (Dall)
Colus spitzbergensis (Reeve)
C. herendeenii (Dall)
C. roseus (Dall)
C. hypolispus (Dall)
C. aphelus (Dall)
C. halli (Dal!)
C. dautzenbergi (Dall)
Liomesus nassula (Dall)
L. ooides (Middendorff)
Neptunea lyrata (Gmehn)*
N. ventricosa (Gmelin)*
A^. pribiloffensis (Dall)*
N. borealis (Philippi)
A'^. heros (Gray)*
Plicifusus kroyeri (Moller)*
P. incisus (Dall)
P. brunneus (Dall)
Pyrulofusus harpa (Morch)
P. deformis (Reeve)*
P. melonis (Dall)
Volutopsius fragilis (Dall)*
V. middendorfii (Dall)*
V. trophonius (Dall)
V. castaneus (Dall)
V. filosus (Dall)
Family Volutidae
Arctomelon stearnsii (Dall)
Family Volumitridae
Volumitria alaskana (Dall)
Family Cancellariidae
Admete couthouyi (Jay)
Family Turridae
Aforia circinata (Dall)
Antiplanes thalaea (Dall)
Oenopota harpa (Dall)
Obesitoma simplex (Middendorff)
Family Pyramidellidae
Odostomia spp.
1220 Benthic biology
SPECIES ASSOCIATIONS
It has long been recognized that species of marine
benthic invertebrates often occur together as groups
over broad geographical areas. Such groups, variously
referred to as communities, assemblages, biocenoses,
or faunistic complexes, primarily result from similar
tolerances of their component species to environ-
mental variables, although within limited areas,
competition and predation may also play a significant
role. To the extent that group cohesiveness is envi-
ronmentally determined, the area occupied by a
group can be considered as a specific habitat type or
faunistic region. Previous research on the distribution
of benthic fauna in the eastern Bering Sea suggests
that there are at least three (Nagai and Suda 1976) or
possibly four (Neiman 1963) distinct faunistic regions
which appear to be associated with the distribution of
temperature near the sea bottom.
Early attempts at recognizing species groups
undoubtedly involved comparing species distribution
maps. Recently, marine ecologists have accomplished
this by using computer techniques, especially hier-
archical cluster analysis (Clifford and Stephenson
1975), which groups species with similar patterns of
abundance over a number of sampling sites (Field
1971, Day et al. 1971, Hughes and Thomas 1971).
Grouping species in this manner appears biologically
sound, since similarities in distribution patterns
strongly suggest a common response to some (usually
unknown) suite of environmental variables. An
alternative approach used in this study consists of
grouping species according to the similarity of envi-
ronmental variables measured at sampling sites where
each species occurred (Somerton and Macintosh, in
preparation). Rather than grouping species by their
abundances, which may not be associated with
environmental variables, this new method allows
grouping by an explicit set of niche or habitat
variables.
The environmental variables used to group snails
are two aspects of temperature: the annual maxi-
mum bottom temperature and the maximum rate of
warming. These variables were chosen because they
are considered to be important determinants of
benthic invertebrate distribution (Nagai and Suda
1976, Neiman 1963) and because bottom-temperature
measurements for the eastern Bering Sea were readily
available (Ingraham 1973). Although other environ-
mental variables may affect snail distribution, we
have restricted our investigation to examining how
various snail species distribute themselves within a
heterogeneous thermal regime.
Large Bering Sea snails are probably long-lived and
certainly have a limited ability to move in response to
temperature changes. Therefore, long-term average
temperatures were considered more appropriate for
grouping species than temperature measurements
made at the time samples were collected. Maps of
monthly average bottom temperatures by quadrangles
of 1° were available from Ingraham (1973); however,
only data for May through August were sufficient to
construct a reliable picture of the temperature
distribution. Although the maximum bottom tem-
peratures are probably not reached by August,
the distribution pattern of temperature is established
well enough by that time to use as an index of the
yearly maximum. The maximum rate of warming
was chosen to be the difference between August and
July temperatures. To further smooth the data and
allow interpolation of temperatures at the sam-
pling sites, a fifth-order polynomial in latitude and
longitude, sometimes known as a trend surface,* was
fitted to both August temperatures and July-August
temperature differences. The observed spatial dis-
tributions of the 15 most abundant snail species (Fig.
68-1) were then translated into a collection of maxi-
mum temperature and maximum warming values by
evaluating each polynomial at all sites at which a
given species was observed. For example, Neptunea
heros, observed at 134 of 344 sampling sites, was
represented by a set of 134 maximum temperature/
maximum warming data pairs.
Arranging species into groups was accomplished in
two stages. First, a measure of dissimilarity, the
Mahalanobis distance, "D" (Morrison 1976), was
calculated for all pairs of data sets. This distance
measure was chosen in preference to the more famil-
iar Euclidean distance (Clifford and Stephenson
1975) because it scales the Euclidean distance be-
tween data sets by their covariance (Morrison 1976).
Group average sorting, one method of hierarchical
cluster analysis (Clifford and Stephenson 1975), was
used to join species into progressively larger groups.
The sequence from many small homogeneous groups
to one heterogeneous group is shown as a dendrogram
in Fig. 68-2.
Choosing the level of dissimilarity at which to
interpret the group structure of such a dendrogram
involves some judgment. Groups of two or three
closely associated species are formed at low levels of
dissimilarity. In Fig. 68-2, five pair -groups of species
are evident: N. heros and N. uentricosa, P. kroyeri
and B. scalari forme, C. magna and B. angulosum, V.
' Trend surface analysis is discussed in SYMAP User Reference
Manual, available through the Laboratory for Computer
Graphics and Spatial Analysis, Harvard University.
Large marine gastropods 1221
DISSIMILARITY LEVEL
0.0 0,1 0 2 0 3 0,4 0,5 0.6 0.7 0.8 0.9
I 1 \ 1 \ 1 1 \ 1 1
GROUP 2
IN. heros
N. ventricosa
P. deform is
N. I y rata
8. scatariforme
P. kroyeri
N. pribiloffensis
B. beringii
F. oregonensis
B. plectrum
V. middendorfii
B. angulosum
C. magna
B. polare
v. fragHis
D-
D-
1
Figure 68-2. Dendrogram showing the similarity of fif-
teen species of snails. Groups labeled 1 through 4 occur at
a dissimilarity level of 0.5.
fragilis and B. polare, and N. pribiloffensis and
B. beringii. The species in these groups are quite
similar in the environmental variables which join
them and, as can be seen in Fig. 68-1, are also distrib-
uted similarly. At higher levels of dissimilarity,
species are joined that do not have identical distribu-
tions. Thus, the groups formed at these higher levels
of dissimilarity may have similar temperature toler-
ances but differ in other ecological requirements. If a
dissimilarity level of 0.500 is chosen, then all fifteen
species are included in four distinct groups (Fig.
68-2). The combined distribution of all members of
each group is shown in Fig. 68-3.
Although the four groups appear quite distinct,
they may not be statistically different. Two slightly
different techniques were used to test for statistical
differences. First, Hotelling's "T" (Morrison 1976),
a multivariate extension of Student's "t" distribu-
tion, was used to test whether each group was statis-
tically different from the others when maximum
temperature and maximum warming were considered
simultaneously. The results of these tests indicated
that each group was different from the other three at
a probability level of 0.01. A second method for
testing for differences between groups consisted of
making univariate "t" tests (Sokal and Rohlf 1969)
on each veiriable. This was done because groups
which differ when the variables are considered
simultaneously may not differ when each variable is
tested separately. The results of the univariate "t"
tests are summarized in Table 68-2. If a significance
level of 0.05 is chosen, Groups 1 and 4 do not differ
with respect to either variable. Group 3 differs
from all other groups with respect to both variables,
and Group 2 differs from all other groups in maxi-
mum temperature but differs only from Group 3 in
maximum warming.
Another way of stating these observations is that
the four species groups can be divided into three
distinct levels of maximum temperature and two
distinct levels of maximum warming (Table 68-3).
Although Groups 1 and 4 are statistically distinct
when both variables are considered simultaneously,
they are not different when each variable is consid-
ered alone. If Groups 1 and 4 are combined, then
three distinct faunistic groups exist: one associated
with cold water having a low maximum rate of
warming, a second associated with warmer water also
having a low maximum rate of warming, and a third
associated with the warmest water which has a high
maximum rate of warming.
The thermal characteristics of the three identifiable
faunistic regions result from the manner in which
warming occurs during the summer. In spring, the
temperature above the bottom is uniformly cold from
the shore out nearly to the edge of the continental
shelf, where a northward advection of Pacific Ocean
water causes it to increase slightly. As summer
progresses, shallow nearshore areas are warmed by
insolation. Three types of thermal regions are pro-
duced: the coastal area (inhabited by Group 3),
Figure 68-3. Distribution of the four faunistic groups of
snails in the eastern Bering Sea.
1222 Benthic biology
TABLE 68-2
Summary of univariate "t" tests between all groups taken in pairs.
Shown for each pair of groups are symbols representing the probability levels of tests
on maximum temperature (upper) and maximum rate of warming (lower).
Probability levels associated with each symbol are NS = P > 0.05, * = 0.01 < P < 0.05, ** = P < 0.01.
Group
number
1
2
3
4
Number of
Mean
maximum
observations
temperature
94
1.66
624
2.49
302
3.94
241
1.72
GROUP
2
Mean maximum rate
of warming
0.31
0.63
1.16
0.64
NS
**
**
**
**
NS
NS
**
NS
**
which rapidly warms and reaches the highest tem-
peratures; the central region (Groups 1 and 4), deep
enough to escape much of the summer warming and
relatively unaffected by advected water from the
south ; and the outer continental shelf region (Group
2), maintained at a relatively warm temperature by
advection.
The thermal preferences of the fifteen species of
snails, as indicated by their latitudinal ranges in the
eastern Pacific, eastern Bering Sea, and Alaskan
Arctic, appear to agree with the temperatures at
which they were observed within the study area (Fig.
68-4). The ranges of all Group-3 snails extend from
the Alaska Peninsula northward into the Arctic
Ocean. None have been found in the Gulf of Alaska.
Members of this group are associated with shallow
coastal waters characterized by large seasonal temper-
ature fluctuations. Such temperature changes may be
intolerable for most species and are probably respon-
sible for the fact that relatively few snail species
inhabit the coastal areas. Group-2 snails have wider
and more southern ranges than any other group.
Although three of the six species in this group are
found in the Arctic Ocean, five occur in the Gulf of
Alaska, and one, Fusitriton oregonensis, occurs as far
south as California. Since at least two species in
this group, F. oregonensis and Neptunea lyrata, occur
80
75°
70°
65°
60°
55°
50°
45°
40°
35°
30°
ARCTIC OCEAN
^■^- <l- -^^ V ^■■^' *•<(•
q" «■ «■ <■■ <)-
V ■^' ^' 0- <!>• -^^
■
f
E.BERING SEA
T
N.E, PACIFIC OCEAr
M
GROUP
3
GROUP
2
GROUPS
1 &4
Figure 68-4. Latitudinal ranges of fifteen species of
snails in the northeast Pacific Ocean, eastern Bering Sea,
and Arctic Ocean off Alaska. Data on ranges are from
Abbott 1974, Golikov 1961, MacGinitie 1959,Macpherson
1971, and Oldroyd 1927.
in shallow water south of the Alaska Peninsula, they
may inhabit the relatively deep water along the
outer continental slope because there is no strong
seasonsd cooling there. Groups 1 and 4 have ranges
Large marine gastropods 1223
TABLE 68-3
Summary of significant differences (P<0.05) between groups,
showing the arrangement of the four groups into
three distinct categories of maximum temperature and two
distinct categories of warming rate
Maximum rate of warming
Small
Large
Maximum
Temperature
Cold
Warmer
Warmest
1,4
2
intermediate between the two others, and it is inter-
esting that they contain all three of the species
studied which can be regarded as endemic to the
Bering Sea. Thus, the coastal areas are inhabited
by species whose ranges extend into the Arctic, the
deeper areas are inhabited by species whose ranges
extend south of the Alaska Peninsula, and the peren-
nially cold central region is inhabited by species
which tend to be endemic.
Previous studies of the distribution of benthic
invertebrates in the eastern Bering Sea have shown
patterns similar to those shown in Fig. 68-3. Neiman
(1963) defined four zoogeographic complexes of
benthic invertebrates in the Bering Sea: Pan-Arctic
complex in the cold central region, sub-Arctic-Boreal
complex on the upper portion of the continental
slope where there is relatively warm water of constant
temperature, Arctic-Boreal complex in a region
intermediate between Pan-Arctic and sub-Arctic-
Boreal, and low-Arctic-Boreal complex in shallow
water which heats down to the bottom in summer.
Nagai and Suda (1976) discussed the distribution of
snails and bivalves in the Bering Sea and defined three
distributional zones: coastal, cold water, and deep.
Although the geographical area assigned to each of
these three zones was not as similar to that shown in
Fig. 68-3 as Neiman 's (1963) faunal regions were, the
general pattern was still the same.
Our results, in conjunction with the findings of
Neiman (1963) and Nagai and Suda (1976), sup-
port the hypothesis that three identifiable thermal
regions exist in the eastern Bering Sea during the late
summer and that associated with each region is a dis-
tinct assemblage of snail species. Furthermore, from
the ranges of these species, the Bering Sea appears to
be a transition region where both boreal and arctic
species occur within their specific thermal habitats.
LIFE HISTORIES
Relatively little is known about the life histories of
the 15 common large eastern Bering Sea snails dis-
cussed here. All but Fusitriton oregonensis^ are
dioecious, are fertilized internally, and produce egg
clusters from which crawling young are hatched.
Thorson (1950) and Shuto (1974) discussed the lack
of a pelagic larval stage (lecithotrophic development)
among some prosobranch gastropods and its effect on
their evolution and distribution. Members of the
genus Neptunea have a fairly protracted spawning
period; Neptunea capsules at all stages of develop-
ment can be found in the eastern Bering Sea from
June through August (personal observation). Golikov
(1961) reported the spawning period of four Nep-
tunea species in the eastern Bering Sea as ranging
from 2.5 to 5 months with no spawning before the
end of May or after October. Neptunea lyrata
hatched after about three months of capsule life. In
more temperate Danish waters, Pearce and Thorson
(1967) found that N. antigua (L.) spawn from Febru-
ary through April and have a capsule life of about six
months. Neptunea species in the Bering Sea may
have a longer capsule phase; a N. ventricosa cluster
containing embryos with calcified shells was collected
in July and held in an aquarium at 5 C for six months
before hatching (personal observation).
The capsules and clusters of 6 of the 15 large,
common eastern Bering Sea snails have been de-
scribed: Neptunea lyrata, N. heros, and N. ventricosa
by Golikov (1961); Pyrulofusus deformis by Conor
(1964); Fusitriton oregonensis by Howard (1962);
and Beringius beringii by Macintosh (1979). In the
eastern Bering Sea, clusters are usually laid on the
shells of large snails, but they are also occasionally
found on rocks, waterlogged wood, and debris of
human origin. The high incidence of clusters on snail
shells may simply reflect the scarcity of other hard
stable surfaces in the environment. Egg clusters of
the various species vary considerably in size, shape,
color, and number of individual capsules. Group
spawning must occur among some of the Buccinum
species, because, although females seldom exceed
70 g in weight, round clusters of egg capsules weigh-
ing over 4 kg and containing thousands of capsules
have been found (personal observation). Number of
capsules per cluster and number of well-developed
embryos per capsule for three of the four large
eastern Bering Sea. Neptunea are shown in Table 68-4.
^Fusitriton, a member of the tropical family Cymatiidae,
lays a cluster of capsules from which pelagic larvae hatch.
(Personal communication, Dr. Alan Kohn, University of
Washington, Seattle.)
1224 Benthic biology
TABLE 68-4
Number of well-developed embryos per capsule and number of capsules per cluster
in three species of eastern Bering SeaNeptunea.
N. pribiloffensis
N. heros
N. ventricosa
No. of clusters examined
Capsules per cluster— range
Capsules per cluster— mean
Embryos per capsule— range
Embryos per capsule— mean
7
74-134
103
0-6
3.2
3
27-41
34
0-7
3.4
5
37-111
81
1-4
2.9
Because some clusters may be the product of more
than one female and females may lay more than one
cluster per spawning season (see Pearce and Thorson
1967), it is difficult to determine the net production
of young per female.
Aging of neptunid and buccinid snails is difficult
and has been successfully accomplished only for
Babylonia japonica (Reeve), a small (<70 mm) fast-
growing buccinid found in shallow waters along the
coast of Japan (Kubo and Kondo 1953). Pearce and
Thorson (1967) speculated that large, sexually
mature specimens of Neptunea antigua from Danish
waters were about 10 years old. In that study, N.
antigua were about 10 mm long at hatching and grew
10-20 mm in a year.
Some eastern Bering Sea Neptunea, N. heros in
particular, have opercula with well-defined growth
rings on the exterior surface; but it is not certain
whether these rings represent annular growth. If they
do, then animals approximately 110 mm in length are
more than 15 years old.
Size at maturity of the four large eastern Bering
Sea Neptunea has been documented by Macintosh
and Paul (1977). Female N. heros, N. lyrata, N.
pribiloffensis, and N. ventricosa were found to
mature at 110, 110, 105, and 102 mm, respectively;
corresponding lengths of males were 95, 100, 90, and
87 mm. Females of all four species examined appear
to mature at shell lengths 10-15 mm greater than
males of the same species. Pearce and Thorson (1967)
found mature female N. antigua in Danish waters to
be larger than males. They also reported that females
did not feed during the average 21 days of capsule-
laying and that most females subsequently died be-
cause of the rigors of spawning. Shimek (1979)
similarly found that females of N. lyrata and N.
ventricosa probably do not feed during the prespawn-
ing and spawning period. He speculated that this,
coupled with the need to produce many large yolky
eggs, tends to select for large females with increased
energy reserves.
Shimek (1979) reported that the diets of A^. prib-
iloffensis, N. lyrata, N. heros, and N. ventricosa in the
eastern Bering Sea consisted of a variety of organisms
including polychaetes, bivalves, barnacles, fishes, and
crustaceans (Table 68-5). Other studies of the diets
of related species suggest that snails are scavengers
and facultative predators (Blegvad 1914, Hunt 1925,
Avery 1961, Pearce and Thorson 1967).
JAPANESE FISHERY
Japan has commercially harvested snails in the
eastern Bering Sea since at least 1971 (Macintosh
1980). The fishery occurs east of 175°W on the
continental shelf northwest of the Pribilof Islands.
Nagai described several aspects of the commercial
fishery, including gear, species captured, size-compo-
sition of the catch (1974), incidental catch (1975a),
and catch-per-unit-effort (1975b). Statistics available
since 1972 indicate that about 3,000 mt of edible
snail meats (11,000 mt live weight) were harvested
each year from 1972 through 1975 (Table 68-6).
Total weight and recovered meat weight data from
the 1974 harvest indicate an edible meat recovery of
27 percent. This value is similar to values of edible
meat recoveries of from 26.8 to 30.6 percent ob-
tained by Macintosh and Paul (1977) for four species
of eastern Bering Sea Neptunea.
The most common gastropod in Japanese catches
made northwest of the Pribilof Islands in 1973 was N.
pribiloffensis, about 70 percent of the catch by
weight (Nagai 1974). Buccinum angulosum and B.
scalariforme accounted for an additional 23 percent
of the catch.
In 1977 Japan began to supply the United States
with statistics on the number of vessels and amount
of effort expended in the eastern Bering Sea snail
fishery. Vessels licensed for this fishery range from 96
to 490 gross mt and from 25 to 50 m in length.
Between June and October 1977, three vessels caught
404 mt of edible meat, approximately 15 percent of
Large marine gastropods 1225
TABLE 68-5
Diets of four eastern Bering Sea Neptunea expressed as the number of each species
examined containing a given item (from Shimek 1979).
Contents
N. pribiloffensis
N.ly
Nothing
71
92
Tissue
3
12
Tissue and Sand
7
15
Sand
23
28
Polychaetes
21
16
Cuticle
1
8
Bivalves
1
4
Barnacles
0
4
Fishes
0
1
Crustaceans
1
1
N. heros
N. ventricosa
Total
73
21
12
16
12
3
2
3
1
3
104
340
29
65
19
53
19
86
14
63
4
16
1
8
10
17
2
4
3
8
Japan's 3,000 mt quota. The vessels had an average
catch of 2.7 mt of meat per day. In 1978, a maxi-
mum of nine vessels caught 2,200 mt of edible meat
between May and November. The average catch rate
during the 1978 fishery was 2.9 mt/d. In 1979 three
vessels caught only 537 mt of edible meat in a fishing
season that began in July and ended in October. The
average daily catch was 2.8 mt of meat per vessel day.
Fishing gear consists of baited pots fished at
intervals on a groundline. The pots are truncated
cones, roughly 88 cm in height, with a single opening
or tunnel approximately 12-15 cm in diameter on the
top. Webbing covering the pot has 6-cm meshes on
the lower 23 cm of the pot and 12-cm meshes on the
remainder.
We know little about Japanese fishing techniques,
but in 1973, one vessel fished about 6,000 pots on 12
groundlines (500 pots/groundline) and took three
days to pick and rebait the entire set of gear. An
average catch rate of 4 kg/pot/3-day soak was re-
ported by that same vessel (Nagai 1975a). In the
1977 fishery, the average catch rate was reported as
0.9 kg/pot/33-hour soak (Unpublished data, NMFS,
1979, Juneau).
All processing of the snail catch now occurs on
board the catcher vessel. This consists of crushing the
shells, briefly cooking the meats, and removing
any soft parts and shell fragments. The meats are
graded by size and quality and quick-frozen in trays.
Small snails in the catch may be frozen whole.
The only available figures on the value of the snail
fishery are derived from estimates of the ex-vessel
price of snail meats. These figures are used by the
United States as a base for calculating fee schedules
for foreign vessels fishing within the extended juris-
diction zone. Estimated ex-vessel prices for the years
1976-78 are $600, $600, and $1,657 per metric ton
of meat. At these ex-vessel prices, the 1976 and 1977
eastern Bering Sea catch was worth $242 thousand,
the 1978 catch was worth $1.3 million, and the 1979
catch was worth $890 thousand.
Until recently, there was no U.S. regulation of the
eastern Bering Sea snail fishery. Implementation of
the Fishery Conservation and Management Act
of 1976 provided the United States a tool to monitor
and manage the snail fishery within the 200-mile
conservation zone. A preliminary management plan
developed by NMFS for the Secretary of Commerce
is currently the basis for regulations governing the
fishery. Because there is currently no domestic
TABLE 68-6
Catch and effort statistics of the Japanese snail fishery
in the eastern Bering Sea, 1972-78
Fishing
effort
Catch (mt)
(vessel
Year
edible meat
Total weight^
days)
1972
3,218''
11,900
NA
1973
3,319^
12,300
NA
1974
3,574*'
13,237
NA
1975
3,447b
12,767
NA
1976
NA=
NA
NA
1977
404'^
1,500
152
1978
2,184«i
8,100
749
1979
537^1
1,990
190
^Values are estimates derived from the weight of edible meat
and whole snails taken by the fishery in 1974.
^Data provided by the Japan Fisheries Agency through the
U.S. Embassy, Tokyo, Japan.
'^NA designates that data were not available.
'^ As reported to the United States under provisions of the
Fishery Conservation and Management Act of 1976.
1226 Benthic biology
fishery for snails in the eastern Bering Sea, the total
allowable catch has been allocated to Japan, the only
nation now involved in the fishery. Japan's 1977-79
quotas were set at 3,000 mt of edible meat, the same
level as the average catch for the years 1972 to 1975.
Changes in total allowable catch and Japan's harvest
level will depend upon newly acquired biological and
socioeconomic data.
PROSPECTS FOR A DOMESTIC SNAIL FISHERY
Clifford, H. T., and W. Stephenson
1975 An introduction to numerical classifi-
cation. Academic Press, N.Y.
Day, J. H., J. G. Field, and M. Montgomery
1971 The use of numerical methods to
determine the distribution of the
benthic fauna across the continental
shelf of North Carolina. J. Animal
Ecol. 40:93-126.
Domestic fishermen and processors have expressed
interest in the Alaskan snail resource, but their future
involvement is less certain than the future involve-
ment of Japan. The rapidly expanding and highly
profitable king and snow crab fisheries are currently
dominating domestic fishing activities. Although crab
vessels would be well suited to snail pot fishing, most
crab fishermen consider fishing for Gulf of Alaska
and eastern Bering Sea bottomfish as an alternate or
supplemental activity. Attempts to initiate a snail
fishery in the Gulf of Alaska have not so far been
productive: they have been exploratory in nature but
show promise as potential off-season operations in
the next few years. Innovative processing and mar-
keting techniques as well as a continued increase in
the value of the traditional frozen meat product will
be necessary conditions for the initiation of a do-
mestic snail fishery.
Feder, H. M., J. Hilsinger, M. Hoberg, S. Jewett, and
J. Rose
1978 Survey of the epifaunal invertebrates
of the southeastern Bering Sea.
In: Environmental assessment of the
Alaskan continental shelf. NOAA/
OCSEAP (Final Rep.), Ann. Rep.
4:1-126.
Field, J. G.
1971
Golikov, A. N.
1961
A numerical analysis of changes in the
soft-bottom fauna along a transect
across False Bay, South Africa. J.
Exp. Mar. Biol. Ecol. 7:215-53.
Ecology of reproduction and the
nature of egg capsules in some gastro-
pod molluscs of the genus Neptunea
(Bolten). Zool. Zh. 40:997-1009.
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Res. Lab. 10:141-56. (Transl.
Language Serv. Div., Off. Int. Fish.,
Nat. Mar. Fish. Serv., NOAA, Dep.
Comm., Washington, D.C.)
1975a An analysis of the snail fishing data in
the eastern Bering Sea. 1. On the
variation of catch per unit effort.
Bull. Far Seas Fish. Res. Lab. 12:121-
35. (Transl. Language Serv. Div.,
Off. Int. Fish., Nat. Mar. Fish. Serv.,
NOAA, Dep. Comm., Washington,
D.C.)
1975b Studies on the marine snail resources
in the eastern Bering Sea. 2. List of
Gastropoda and Bivalvia (Mollusca)
species collected with snail-baskets
and some information about the
incidental catch in the adjacent waters
of the Pribilof Islands, 1973. Bull.
Far Seas Fish. Lab. 12:137-143. (In
Japanese, Eng. abs.)
Nagai, T., and O. Arakawa
1978 Survey report on the sea snail re-
sources in the eastern Bering Sea,
using the Meiko Maru No. 7 during
the summer of 1978. Bull. Far Seas
Fish. Res. Lab. 168:1-45. (In Japan-
ese, Eng. abs.)
McLaughlin, P. A.
1963 Survey of the benthic invertebrate
fauna of the eastern Bering Sea. U.S.
Fish Wildl. Serv., Spec. Sci. Rep.,
Fish. No. 401.
Morrison, D. F.
1976 Multivariate statistical
McGraw-Hill, N. Y.
methods.
Nagai, T., and A. Suda
1976 Gastropods and bivalves in the eastern
Bering Sea in summer with reference
to their environment as seen from
incidental trawl catches. Bull. Far
Seas Fish. Res. Lab. 14:163-79.
(Transl. Language Serv. Div., Off. Int.
Fish., Nat. Mar. Fish. Serv., NOAA,
Dep. Comm., Washington, D.C.)
1228 Benthic biology
Neiman, A. A.
1963 Quantitative distribution of benthos
on the shelf and upper continental
slope in the eastern part of the Bering
Sea. In: Soviet fisheries investiga-
tions in the northeast Pacific, P. A.
Moiseev, ed., 1: 143-217.
Shimek, R.
1979
Oldroyd, I. S.
1927
The marine shells of the west coast of
North America. Gastropoda and
Amphineura. Stanford Univ. Pub.,
Univ. Series, Geol. Sci. 2.
Pearce, J. B.. and G. Thorson
1967 The feeding and reproductive biology
of the red whelk, Neptunea antigua
(L.), (Gastropoda, Prosobranchia).
Ophelia 4:277-314.
Pereyra, W. T., J. E. Reeves, and R. C. Bakkala
1976 Demersal fish and shellfish resources
in the eastern Bering Sea in the
baseline year 1975. Nat. Mar. Fish.
Serv., Northwest Fish. Cent., NOAA
U.S. Dep. Co mm., Seattle, Wash.,
Proc. Rep.
Shuto, T.
1974
Diets, morphology and competitive
displacement of four species of Bering
Sea whelks (Gastropoda: Buccinidea:
Neptunea). Unpub. MS., Univ. of
Alaska, Anchorage.
Larval ecology of prosobranch gastro-
pods and its bearing on biogeography
and paleontogy. Lethaia 7:239-56.
Sokal, R. R., and F. J. Rohlf
1969 Biometry.
Francisco.
W. H. Freeman, San
Somerton, D. A., and R. A. Macintosh
A classification of snail species based
on niche and habitat variables (in
prep.).
Thorson, G.
1950
Reproductive and larval ecology of
marine bottom invertebrates. Biol.
Rev. 25:1-45.
Feeding Interactions in the Eastern Bering Sea
with Emphasis on the Benthos
Howard M. Feder and Stephen C. Jewett
Institute of Marine Science
University of Alaska
Fairbanks
ABSTRACT
The Bering Sea contains some of the world's largest stand-
ing stocks of commercially exploitable shellfish and finfish
species. Many of these species feed on benthic organisms.
The benthos of the northeastern Bering Sea, which accounts
for 86 percent of the total benthos on the eastern shelf,
supports reduced numbers of demersal fishes, presumably due
to low-temperature barriers normally present. In the south-
eastern Bering Sea, where 23 percent of the food benthos of
the eastern shelf is found, bottom fishes have year-round
access to food resources. Major fisheries for crabs and bottom
fishes occur in the southeastern portion of the Bering Sea.
Most bottom predators feed on the upper continental slope
in winter, but move to shallower and warmer waters of the
shelf in late spring and summer. Slow growth is characteristic
of benthic invertebrates used as food on the Bering Sea shelf.
However, bottom-feeding species on the slope and the shelf
edge probably also eat zooplankters, as these organisms
accumulate on the bottom after death. Periodic organic
carbon enrichment of the shelf, resulting from a poorly
coupled organic carbon system, also enhances food resources
on the bottom and may result in more frequent recruitment
successes for infaunal species; densities of Clinocardium
ciliatum as high as 3,000/m' are reported on the southeastern
Bering Sea shelf. Organic carbon enrichment of the south-
eastern Bering shelf is indicated by dense populations of
deposit-feeding bivalve mollusks, a general increase of other
infauna, and high densities and biomass of epifauna.
Bivalve mollusks, one of the most commonly consumed
prey in the Bering Sea, are a resource for which crabs, sea
stars, bottom fishes, and marine mammals compete. In the
northern part of the Bering Sea, where low water tempera-
tures prevail, sea stars, walruses, and bearded seals are domi-
nant bottom predators. In warm years flatfishes invade the
northern shelf in summer and compete for bivalve resources.
The major bottom fish of the Bering Sea are sculpins, blennies,
eelpouts, snailfishes, cods, and flatfishes. Most of these prey
on benthic invertebrates and other fishes. Opportunistic
feeding seems to be common for bottom-feeding invertebrates,
fishes, and marine mammals. Food data indicate a broad
spectrum of prey used by benthic organisms in the Bering
Sea.
The role of gametes and marine larvae as carbon resources
in the sea is discussed. It is suggested that pulses of high-
energy reproductive material, available during spawning of
large populations of benthic marine organisms (e.g., sponges,
sea anemones, annelids, mollusks, and sea stars), are important
in secondary production.
Many studies have been conducted on predator-prey
interactions in marine systems, but such studies are not
generally used to interpret the effect of human harvest of
ocean products. Improvement of fisheries management tools
may, in part, be brought about by a better understanding of
major organic carbon pathways in the Bering Sea shelf system.
INTRODUCTION
The high productivity of the benthos of the
southeastern Bering Sea (Hood and Kelley 1974,
Bakkala and Smith 1978) implies a substantial and
consistent influx of organic carbon to the sea floor.
In order to comprehend the source and flow of that
carbon to the bottom and trace the flow through the
benthic system, it is necessary to understand (1) the
physical, chemical, geological, and biological proc-
esses operating on the bottom, (2) the climatic
patterns and oceanographic processes that integrate
the benthic system, and (3) the food regimes and
feeding dynamics of organisms present. The physical,
chemical, geological, and biological processes, as well
as the oceanographic and climatic features of the
eastern Bering Sea, are treated elsewhere in this book
(see also Hood and Kelley 1974 and Iverson et al.
1979). Preliminary assessments of predator-prey
interactions in the Bering Sea are available (e.g.,
Feniuk 1945, Takeuchi 1959, Neiman 1963, Skalkin
1963, Cunningham 1969, Mito 1974, Tarverdieva
1976, Fay et al. 1977, Feder and Jewett 1978,
McConnaughey 1978; see also Feder and Jewett
1980, for a literature review). Outer Continental
Shelf Environmental Assessment Program (OCSEAP)
studies in the Bering Sea have broadened our knowl-
edge of the feeding strategies of common benthic
invertebrates, demersal fishes, birds, and mammals
(Pereyra et al. 1976; Sanger and Baird 1977a and b;
Smith et al. 1978; Lowry et al. 1979; Feder and
Jewett 1978, 1980; Feder et al. 1980a; Jewett and
Feder 1980).
This chapter examines (1) the food habits of ben-
thic invertebrates, demersal fishes, and marine mam-
mals and birds, (2) general aspects of organic carbon
coupling between the water column and the benthos,
and (3) predator-prey interactions within the benthic
system of the Bering Sea. Species examined in detail
are of commercial or ecological importance, or
both. Data are derived from literature sources and
OCSEAP studies.
1229
1230 Benthic biology
FOOD HABITS
General
The flow of organic carbon to the sea floor is of
varying quality and quantity, and depends on the
interaction of many environmental factors in space
and time (see Parsons et al. 1977, for a general
discussion of benthic systems). The presence, rela-
tive abundance, and biomass of benthic species
largely reflect the adequacy of the carbon resources
available. Thus, benthic organisms, responding to a
variable carbon supply, are never uniformly distrib-
uted over the sea bottom, and any one of a variety
of species may be dominant at any place and time.
Benthic species, particularly infauna, are typically
aggregated (see discussions in Holmes and Mclntyre
1971 and Downing 1979). Similar aggregations of
benthic species are apparent in the eastern Bering
Sea (Feder and Jewett 1978, 1980; Stoker, Chapter
62; Haflinger, Chapter 63, this volume), although
organisms there are also responding to a combination
of oceanographic features unique to that sea.
Investigations summarized in Iverson et al. (1979)
have established the presence of three oceanic fronts
in the southeastern Bering Sea (see also Section I,
Volume 1). A front at the shelf break (200 m)
represents a transition between oceanic and sheLf
waters (Kinder and Coachman 1978). Shoreward
of this front is a middle-shelf front near the 100-m
isobath (Coachman and Charnell 1979). An inner
front is located near the 50-m isobath (Schumacher
et al. 1979). The zone seaward of the middle front
contains a mixture of Bering Sea and Alaskan Stream
water, and the shelf water shoreward of this front
is strongly influenced by winter cooling, sea-ice
formation, storms, and seasonal variations in the
influx of fresh water from rivers (Coachman and
Charnell 1977). It is suggested by Iverson et al.
(1979) that major food webs leading to large stocks
of pelagic and benthic fauna are separated on the
shelf in relation to the fronts in the southeastern
Bering Sea (see Section I, Volume 1 and Sections
VII and X, this volume, for additional background
information).
The broad Bering Sea shelf is unique in the pres-
ence of a seasonal ice cover whose extent varies from
year to year (see Section I, Volume 1 and Niebauer,
1980). The first significant primary production
takes place on the undersurface of the ice (Alexander
and Chapman, Chapter 45, this volume). Intense
phytoplankton blooms occur at the retreating ice
edge for short periods of time in the spring, and
production rates exceeding 25 mg C/m^/hr during a
period of two to three weeks have been measured in
surface waters (Section VII, this volume and
Alexander and Niebauer, in press). Phytoplankton
productivity £ind standing-crop levels at the ice edge
and elsewhere on the Bering Sea shelf are affected by
the types, distribution, and abundance of pelagic
grazers present. Cooney (1978) demonstrated two
distinct copepod communities over the southeastern
Bering Sea shelf: an oceanic group of large species
seaward of the middle front and a shelf group of
small grazers. The former group effectively grazes the
phytoplankton present and forms the biological base
for an extremely productive pelagic fauna over the
outer shelf. Because the large phytoplankton biomass
of the middle-shelf zone is not effectively grazed by
the small herbivores present, phytoplankton accumu-
late and settle to the bottom (Iverson et al. 1979; see
also Walsh et al. 1978 for a discussion of this process
in other shelf systems). Such a flow of autoch-
thonous carbon to the middle-shelf zone is reflected
by rich standing stocks of tnfaunal, epifaunal, and
demersal fish (Bakkala and Smith 1978, Feder et al.
1980a, Feder and Jewett 1980). The benthic infaun-
al biomass of the middle-shelf zone reaches a maxi-
mum where frontal structure is particularly well
developed (Haflinger 1978, Iverson et al. 1979, Feder
et al. 1980a, Coachman and Charnell 1979). Fur-
thermore, Alexander and Cooney (1979) and
Alexander and Niebauer (in press) suggest that the
stabilizing effect of sea ice on the water column in
cold years results in an intense bloom over a short
period with a large part of the phytoplankton settling,
ungrazed, to the bottom. Stable water masses at the
ice edge in cold years probably also result in better
survival of larvae of pelagic and benthic species (see
Ishimaru 1936, Lasker 1975, and Paul et al. 1979a,
for discussions of larval survival and oceanographic
conditions in the sea). Areas not covered by ice in
warm years probably show slower but more sustained
primary production.
Organic carbon on the eastern Bering Sea shelf
may also be derived from remote regions (alloch-
thonous) such as river systems (especially the Kvichak,
Nushagak, Togiak, Kuskokwim, and Yukon Rivers)
and sea-grass beds in several large estuaries along the
Alaska Peninsula. The distribution of allochthonous
carbon and associated sediments over the shelf is
controlled primarily by tidal movements, dominant
currents, and the dispersive action of storms (Sharma
et al. 1972). Suspended particulates in the water
column vary seasonally: they are low during the
period of ice cover but increase during spring phyto-
plankton blooms and storms (Sharma 1972). Fur-
thermore, benthic organisms are displaced laterally
over shallow marine shelves during storms (see Feder
Feeding interactions with emphasis on the benthos 1231
and Schamel 1976 and Rees et al. 1977 for general
discussions), a process that may be of importance
in the Bering Sea. Such a relatively rapid method of
dispersion of adults in benthic populations represents
a potentially important alternative recruitment
strategem in shallow marine benthic systems.
Carbon resources are available to benthic organisms
from the sediment or the water column, or both, as
dissolved organic compounds, organics adsorbed to
sediments, detrital particles, fecal pellets, and living
organisms. The proportions of carbon available in one
or more of these forms are generally characteristic of
certain bottom regimes, and are related to a variety of
factors (Trask 1939, McCave 1976) such as (1)
physical oceanographic features, (2) source of alloch-
thonous carbon, (3) productivity and carbon coupling
in the overlying water column, (4) settlement rates of
particulates, (5) sediment dynamics and lithology,
(6) depositional chemistry and microbiology, and (7)
sediment resuspension mechanisms. Inshore areas in
the Bering Sea (nearshore approximately to the 50-m
isobath) are generally turbulent regions characterized
by sandy sediments and heavy particulate loads in the
water column. A variety of planktonic organisms and
suspended organic particulate materials are available
in the water column as food, and suspension-feeding
organisms (e.g., clams and tunicates) are common.
Offshore, in deeper waters of the shelf (e.g., the
mid -shelf zone of the southeastern Bering Sea), fine
sediments predominate; this area is a relatively
stable environment and is enriched by settlement of
detrital materials of terrigenous and local biogenous
origin. Deposit- feeding polychaetous annelids and
clams are common to these offshore shelf areas (see
Haflinger Chapter 63, McDonald et al.. Chapter 66,
this volume, for further comments on sediments of
the southeastern Bering Sea shelf; see also Feder and
Jewett 1980 and Feder et al. 1980a for distribution
of benthic fauna of the southeastern Bering Sea).
Although epibenthic invertebrates, demersal fishes,
and marine mammals of the Bering Sea shelf, as else-
where, are continuously moving about in search of
food, many organisms (e.g., crabs, bottom fishes,
and walruses) are restricted for part of the year to
limited, often predictable areas of the shelf (Fay
1957, Bakkala and Smith 1978). Although in these
areas predators take a variety of organisms (Skalkin
1963), they often select some species in preference
to others. For example, the red king crab (Para-
lithodes camtschatica) in certain regions of the
southeastern Bering Sea may feed almost exclusively
on a cockle (Clinocardium ciliatum) (Feder and
Jewett 1980, Feder et al. 1980a), whereas in lower
Cook Inlet (Northeastern Gulf of Alaska) the king
crab may select acorn barnacles (Balanus crenatus)
when it encounters large populations (Feder et al.
1980a). The snow crab Chionoecetes opilio in the
southeastern Bering Sea feeds mainly on polychaetes,
brittle stars (Ophiura), and clams (Macoma spp.);
a clam (Nucula tenuis) is the dominant food of snow
crabs in the northeastern Bering Sea (Feder and
Jewett 1978). Thedominantfoodsof starry flounders
(Platichthys stellatus) in the northeastern Bering Sea
are a clam (Yoldia hyperborea), a brittle star (Diam-
phiodia craterodmeta), and a sand dollar (Echinar-
achnius parma) (Feder and Jewett 1978); in the
southeastern Chukchi Sea they eat mainly the pro-
boscis worm (Echiurus echiurus alaskensis) and the
prickleback fish (Lumpenus fabricii).
Carbon flow to the benthos is a complex and
variable process. The qualitative presentations of
food data below represent preliminary steps needed
to understand the quantitative flow of carbon within
the Bering Sea ecosystem.
Species accounts
The data summarized here illustrate many of the
generalizations discussed above, and indicate the
broad spectrum of prey used by benthic invertebrates
and demersal fishes in the Bering Sea. The species
interactions presented are not intended to be ex-
haustive, but are chosen to show generalized, quali-
tative linkages between predator and prey species.
The trophic links between species are summarized
in Fig. 69-1. Food webs for selected species of
commercial or potential commercial value— king
crab (Paralithodes camtschatica), snow crab (Chio-
noecetes spp.), walleye pollock (Theragra chalco-
gramma). Pacific cod (Gadus macro cephalus), and
yellowfin sole (Limanda aspera)—aie included in
Figs. 69-2 to 69-6.
Invertebrates
Pink shrimp (Pandalus borealis). The only available
feeding data for Alaskan pink shrimp aire from
Kodiak Island waters in the western Gulf of Alaska
(Feder and Jewett 1981) and Cook Inlet (Crow
1977, Rice et al. 1980). Stomachs of pink shrimp
from Izhut Bay of Afognak Island and Kiliuda Bay
of Kodiak Island most frequently contained diatoms,
crustacean remains, and filamentous algal fragments.
Foraminifera, tintinnids, polychaetes, and small
bivalves also commonly occurred. Pink shrimp from
the outer shelf of Kodiak Island most frequently
contained remains of crustaceans, bivalves, and fishes.
Sediment was an important component in stomachs
of shrimp from both inshore and offshore areas.
Pink shrimp from Cook Inlet contained 28 food
categories with diatoms, polychaetes, and crusta-
ceans most frequently found. Stomach contents
1232 Benthic biology
BERING SEA
Generalized Food Web
Figure 69-1. A generalized food web for the eastern Bering Sea. See text for discussion and references for data sources.
typically contained sediment (up to 60 percent of dry
weight of contents).
Pink shrimp are used as food by many demersal
fishes, including walleye poUock (Theragra chalco-
gramma). Pacific cod (Gadus macro cephalus), rex
sole (Glyptocephalus zachirus), yellowfin sole
(Limanda aspera), flathead sole (Hippoglossoides
elassodon), and Eirrowtooth flounder (Atheresthes
stomias).
Red king crab (Paralithodes camtschatica). The
food habits of the red king crab, a major component
of the invertebrate biomass in the Bering Sea (Pereyra
et al. 1976, Feder and Jewett 1980a), have been
examined intensively by numerous investigators.
Tarverdieva (1976) investigated the food of the red
king crab in the southeastern Bering Sea, and found
the main foods to be polychaete worms, sand dollars
(Echinarachnius parma), gastropods of the families
Trochidae and Naticidae, and pelecypods, of which
Yoldia, Nuculana (= Leda), Nucula, and Cyclocardia
(= Venericardia) were most often noted. Cunningham
(1969) determined that echinoderms (a brittle star,
Ophiura sarsi, a basket star, Gorgonocephalus sp., a
sea urchin, Strongylocentrotus sp., and Echinarach-
nius parma) were the most important food, by
percent of total food weight (49.1 percent), in the
crab stomachs analyzed. He found that the percent
frequency of occurrence of echinoderms in stomachs
was 81 percent. Mollusks {hivslves— Nuculana radiata,
Clinocardium calif orniense, Chlamys sp.; snaUs—
Solariella sp. and Buccinidae) and crustaceans (crabs—
Hyas coarctatus alutaceus, Erimacrus isenbeckii, and
Pagurus sp.; and sand fleas— Amphipoda) were next in
importance by weight with 37.2 percent and 10.1
percent, respectively (Cunningham 1969). The
percent frequencies of occurrence for mollusks and
crustaceans were 86 and 48 percent, respectively.
McLaughlin and Hebard (1961) determined the
percent frequency of occurrence for foods of male
and female southeastern Bering Sea red king crab.
Feeding interactions with emphasis on the benthos 1233
KING CRAB
PARAL/THODES CAM TSCHA Tl CA
STRONGYLOCENTROTUS
\ ^
PLANT
r
SMALL BENTHIC
ANIMAL REMAINS
DEPOSITED ORGANICS
V
SUSPENDED ORGANICS
MATERIAL
INVERTEBRATES
DETRITUS
BACTERIA
BENTHIC DIATOMS
MEIOFAUNA
PHYTOPLANKTON
200PLANKT0N
Figure 69-2. A food web showing carbon flow to king crab (Paralithodes camtschatica) in the eastern Bering Sea. Bold lines
indicate major food sources.
Primary foods were mollusks (bivalves: 76.9 percent
in males and 60.6 percent in females), echinoderms
(asteroids, ophiuroids, and echinoids: 84.5 percent in
males and 35.6 percent in females), and decapod
crustaceans (shrimps: 26 percent in males and 19.4
percent in females). Polychaetes, algae, and other
crustaceans were next in descending order of impor-
tance. In general, foods were not found to be signifi-
CEintly different between the sexes.
Feder and Jewett (1980) examined the food
of adult red king crab from the southeastern Bering
Sea. The dominant prey items, in decreasing percent
frequency of occurrence, were a cockle (Clinocardium
ciliatum), a snail (Solariella sp.), a clam (Nuculana
fossa), brittle stars (Amphiuridae), a polychaete
worm (Cistenides sp.), and snow crabs (Chionoecetes
spp.).
Feniuk (1945) found mollusks, crustaceans, and
polychaetes, in descending order of importance, to
be the main foods of red king crab from the west
Kamchatka shelf. Takeuchi (1959, 1967) determined
that mollusks, crustaceans, and echinoderms, in
decreasing order of importance, were the major prey
of red king crab of the west Kamchatka coast. Kun
and Mikulich (1954) and Kulichkova (1955) exam-
ined red king crab from the extreme western Bering
Sea. They concluded that the diet of this crab
differs according to geographic region and that the
crab feed on the dominant benthic forms. The most
common food groups were polychaetes, mollusks
(clams— Fo/d/a, Serripes, Siliqua, Tellina; snails—
Polinices, Margarites), Crustacea (Amphipoda,
Cumacea), Echinodermata (Strongylocentrotus,
Asterias, various Ophiuroidea), and Ascidiacea (sea
squirts— Pe/on/a, Boltenia). Tsalkina (1969) reported
that hydroids, primarily Lafoeina maxima, are the
preferred food of early post-larval red king crab of
the west Kamchatka shelf.
The stomach contents of red king crab from the
Gulf of Alaska (waters of Kodiak and Afognak islands)
contained a variety of prey (Feder and Jewett 1981).
Fishes, probably capelin (Mallotus villosus), were
the dominant prey of red king crab in Izhut Bay on
Afognak Island. King crab in Kiliuda Bay on Kodiak
Island mainly preyed upon mollusks, specificadly
clams. King crab taken from the outer Kodiak Shelf
had eaten mainly clams and cockles; however, crus-
taceans and fishes were eiIso important. King crab
collected in shallow bays (5-10 m) of Kodiak Island
mainly fed on clams (primarily Protothaca staminea.
1234 Benthic biology
SNOW CRAB
CHIONOECETES SPP.
SMALL BENTHIC INVERTEBRATES
ANIMAL REMAINS
DEPOSITED ORGANICS
DETRITUS
BACTERIA
BENTHIC DIATOMS
MEIOFAUNA
SUSPENDED ORGANICS
PHYTOPLANKTON
ZOOPLANKTON
Figure 69-3. A food web showing carbon flow to snow crab (Chionoecetes spp.) in the eastern Bering Sea. Bold lines
indicate major food sources.
Macoma spp.), cockles (Clinocardium spp.), and
acorn barnacles (mainly Balanus crenatus). Analysis
of king crab feeding data from the area of Kodiak and
Afognak islands revealed significant differences in
quantity of food consumed between sampling areas,
periods, depths, and crab sizes and classes.
The diet of red king crab from lower Cook Inlet
also reflected regional differences. Crab from Kami-
shak Bay ate mostly barnacles, crab from Kachemak
Bay mostly clams, specifically Spisula polynyma
(Feder et al. 1980b). Post-larval red king crab from
Cook Inlet ingested detrital materials, diatoms,
Bryozoa, harpacticoid copepods, ostracods; all
contained considerable sediment (Feder et al. 1980b).
SCUBA observations have been made near Kodiak
Island of king crab preying on the sea stars Pycno-
podia helianthoides and Euasterias troschelii (Feder
and Jewett 1981, Powell 1979). Remains of sea
stars in crab stomachs are reported by Feder and
Jewett (1981). It appears that predation on these
echinoderms is important, especially when crab are
foraging in shallow waters in late spring and summer
(Feder and Jewett 1981).
The food of the red king crab is similar throughout
its range: polychaetes, mollusks, crustaceans, and
echinoderms are important food resources. King crab
in the Bering Sea must often compete for food with
other bottom-feeding organisms, i.e., snow crabs,
sea stars. Pacific cod, yellowfin sole, Alaska plaice,
rock sole, flathead sole, and rex sole (Feder and
Jewett 1980, Takeuchi 1959).
Various king crab predators have been identified
in the Kodiak area. Powell and Nickerson (1965)
observed horse crab (Erimacrus isenbeckii) preying
on juvenile king crab when a pod disbanded after
being disturbed by divers. The sculpin, Hemilepi-
dotus hemilepidotus, is a known predator of post-
larval king crab 10 mm long (G. C. Powell, personal
communication). As many as five two-year-old king
crab (25 mm carapace length) have been found
in the stomach of a single sculpin, and stomachs of 56
sculpin contained 110 crab (Powell 1974). Pacific
halibut (Hippoglossus stenolepis) are also known to
prey on king crab (Gray 1964). In thousands of
demersal fish stomachs examined from Gulf of Alaska
and Bering Sea waters in the past five years king
crab were rarely found (Feder and Hoberg 1981,
Feder and Jewett 1980, 1981, Feder et al. 1980b,
Jewett 1978). Sea otters feed on mature king crab
(S. C. Jewett, personal observation). King crab are
Feeding interactions with emphasis on the benthos 1235
WALLEYE POLLOCK
THE RAG R A CHALCOGRAMMA
CLUPEA HARE NG US
PALLAS I
CALAMUS
PLUMCHRUS
AND PELAGIC
AMPHIPODA
SMALL BENTHIC
INVERTEBRATES
ANIMAL REMAINS
SUSPENDED ORGANICS
PHYTOPLANKTON
ZOOPLANKTON
Figure 69-4. A food web showing carbon flow to walleye pollock (Theragra chalcogramma) in the eastern Bering Sea.
Bold lines indicate major food sources.
also the target of a major commercial fishery in the
southeastern Bering Sea; 4.9 X 10"* mt were taken in
the 1979-80 fishing season (M. Eaton, Alaska Depart-
ment of Fish and Game, personal communication,
1980).
Snow (Tanner) crabs (Chionoecetes spp.). The
feeding habits of snow (Tanner) crabs, another major
component of the invertebrate biomass in the Bering
Sea (Pereyra et al. 1976, Feder and Jewett 1980),
have been examined by numerous investigators.
These studies imply that food groups used by these
crabs are similar throughout their ranges. Adult Chio-
noecetes bairdi and C. opilio from the southeastern
Bering Sea fed mainly on polychaetes, and young
crabs fed on crustaceans, polychaetes, and mollusks,
in decreasing order of importance (Tarverdieva 1976).
Feder and Jewett (1980) examined the food of
C. opilio from the southeastern Bering Sea, and found
the most frequently consumed foods to be poly-
chaete worms and brittle stars (mainly Ophiura sp.).
The deposit-feeding clam Nucula tenuis domi-
nated the diet of C. opilio from Norton Sound and
the Chukchi Sea (Feder and Jewett 1978). Chio-
noecetes opilio from the Gulf of St. Lawrence fed
mainly on clams (Yoldia spp.) and polychaetes
(Powles 1968). Chionoecetes opilio elongatus from
Japanese waters fed primarily on brittle stars (^ Op /zmra
sp.), young C. opilio elongatus, and protobranch
clams (Portlandia and Nuculana), in decreasing order
of importance (Yasuda 1967). Most of the items con-
sumed by C. bairdi from Kodiak Island in inshore and
offshore waters were polychaetes, clams (Nuculani-
dae), shrimps, crabs, plants, and sediment, in de-
creasing order of importance (Feder and Jewett
1977, 1981). Paul et al. (1979a) examined stomachs
of C bairdi from lower Cook Inlet and found the
main contents to be clams (Macoma spp.), hermit
crabs (Pagurus spp.), barnacles (Balanus spp.), and
sediment, in decreasing order of importance. Chio-
noecetes bairdi in Port Valdez (Prince William Sound)
contained polychaetes, clams, C. bairdi, other crus-
taceans, and detrital material, in decreasing order
of importance (Feder, unpub. data). Snow crabs of
the Bering Sea also compete for food with a variety
of bottom-feeding organisms, as does the king crab.
Snow crabs are one of the most commonly taken
benthic prey in the eastern Bering Sea. They are
fed upon by king crabs, at least six species of fishes
(walleye pollock, Pacific cod, great sculpin. Pacific
halibut, rex sole, rock sole, and flathead sole), and
two marine mammals (walrus and bearded seal).
Besides being taken by these predators, snow crabs
are also cannibalistic. These crabs are also the target
of a major commercial fishery in the eastern Bering
Sea with 5 X 10"* mt harvested in 1979 (J. Reeves,
National Marine Fisheries Service, personal communi-
cation, 1980).
1236 Benthic biology
PACIFIC COD
GADUS MACROCEPHALUS
SAND LANCE
\ \ MISC.
POLLOCK HERRING CAPELIN FISHES
SMALL BENTHIC INVERTEBRATES
ANIMAL REMAINS
ZOOPLANKTON
DEPOSITED ORGANICS
DETRITUS
BACTERIA
BENTHIC DIATOMS
MEIOFAUNA
Figure 69-5. A food web showing carbon flow to Pacific cod (Gadus macrocephalus) in the eastern Bering Sea. Bold lines
indicate major food sources.
Sea stars (Asteroidea). The dominant sea stars
of the eastern Bering Sea, Asterias amurensis, Lep-
tasterias polaris acervata, Evasterias echinosoma,
and Lethasterias nanimensis, are food generalists
(see Sloan 1980 for a general review of the feeding
biology of sea stars). Asterias amurensis examined
from the southeastern Bering Sea fed mainly on
humpy shrimp (Pandalus goniurus) and a sand dollar
(Echinarachnius parma), although a variety of organ-
isms were taken (Feder and Jewett 1980). Asterias
amurensis examined from northeastern Bering Sea
waters consumed a sea urchin (Strongylocentrotus
droebachiensis) and Echinarachnius parma (Feder
and Jewett 1978). Leptasterias polaris acervata
from the southeastern Bering Sea fed solely on a
cockle (Clinocardium ciliatum) (Feder and Jewett
1980), whereas L. polaris acervata from the north-
eastern Bering Sea most frequently consumed Echin-
arachnius parma, barnacles (Balanus spp.), and
cockles (Cyclocardia crebricostata and Serripes
groenlandicus) (Feder and Jewett 1978). Further
north in the Chukchi Sea and Kotzebue Sound, L.
polaris acervata preyed mainly on two ascidians
(Chelyosoma orientale and Boltenia echinata), a
gastropod (Natica clausa), a polychaete worm
(Cistenides sp.), and a clam (Macoma calcarea). Four
other clam species were also taken. Evasterias echino-
soma and Lethasterias nanimensis from the north-
eastern Bering Sea, the Chukchi Sea, and Kotzebue
Sound fed primarily on clams, specifically the
Greenland cockle (Serripes groenlandicus) (Feder and
Jewett 1978).
The diets of Asterias, Leptasterias, Evasterias,
and Lethasterias in the Bering Sea are probably
determined by the relative abundance of prey species.
For example, bivalve mollusks (Tellina lutea, Clino-
cardium ciliatum, Cyclocardia spp., Spisula polynyma,
and Serripes groenlandicus), all potential prey for
sea stars, are widely distributed over the shelf and are
often abundant in some areas (see Feder et al. 1980a;
McDonald et al., Chapter 66, this volume, for data
and maps of the distributions and abundance of clams
in the southeastern Bering Sea). Hughes and Nelson
(1979) state that high densities of sea stars in many
areas of the southeastern Bering Sea are responsible,
through predation, for the low densities of the
Alaska surf clam (Spisula polynyma). Furthermore,
the food requirements for sea stairs, crabs, and some
Feeding interactions with emphasis on the benthos 1237
YELLOWFIN SOLE
LIMANDA ASPERA
MOLGULA
GOMPHINA
FLUCTUOSA
SMALL BENTHIC
INVERTEBRATES
ANIMAL REMAINS
DEPOSITED ORGANICS
DETRITUS
BACTERIA
BENTHIC DIATOMS
MEIOFAUNA
SUSPENDED ORGANICS
Figure 69-6. A food web showing carbon flow to yellowfin sole (Limanda aspera) in the eastern Bering Sea. Bold lines
indicate major food sources.
species of bottom fishes in the Bering Sea are similar
(see section on fishes in this chapter and Pereyra
et al. 1976); thus, the size of sea-star populations
must have an important bearing on the production of
useful crabs and fishes. Sea stars and the Pacific
walrus (Odobenus rosmarus divergens) probably also
compete on occasion for bivalve resources in the
Bering Sea (Fay et al. 1977).
Sea stars are rarely preyed upon as adults, and are,
moreover, generally long-lived organisms (see Feder
and Christensen 1966). Thus, sea stars are generally
considered as sinks whose carbon becomes available
to the benthic system when they die. However, a
considerable portion of sea-star carbon is, in fact,
returned to the sea annually as gamete production
(A. J. Paul and Feder, unpub.). For example,
Hatanaka and Kosaka (1958) calculated that 20-30
percent of the weight of adult Asterias amurensis
in Tokyo Bay is gonadal material which is extruded
during spawning (also see Feder 1956 and 1970,
for comments on the reproductive output of a north-
temperate sea star, Pisaster ochraceus). Sea stars
generally undergo distinct annual reproductive cycles,
and typically shed their gametes into the surrounding
water over short periods of time (Feder 1956,
Boolootian 1966). Such pulses of high-energy
organic material released during spawning of large
1238 Benthic biology
populations of sea stars and other benthic inverte-
brates' not typically used as food by benthic preda-
tors must represent important components of secon-
dary production to the water column and the benthos
(see Isaacs 1976 for a general discussion of this con-
cept; Feder and Jewett 1978, 1980; National
Oceanographic Data Center, NOAA, for distribution
data).
Clams and cockles (Pelecypoda). Bivalve mollusks
(e.g., Nuculana, Nucula, Yoldia, Macoma, Clino-
cardium, Cyclocardia, Serripes, Hiatella, Mya, and
Spisula) are important components of Bering Sea
food webs, and are consumed by crabs, sea stars,
fishes, bearded seal, and walrus. Most of the above
bivalves probably feed by a combination of suspension-
feeding and deposit-feeding methods (Feder, unpub.
data; Rasmussen 1973; Reid and Reid 1969). Conse-
quently, these bivalves are perhaps easily contami-
nated by pollutants (1) in the water column when
suspension feeding (the primary feeding method for
Spisula and Mya), (2) in the sediment when deposit
feeding (the primary method for Nuculana and
Yoldia), or (3) in both water and sediments when
suspension and deposit feeding (e.g., Macoma and
Clinocardium). Thus, increased opportunities for
transfer of petroleum hydrocarbons from bivalves to
their predators can be expected over a long period as
compared to other benthic invertebrates.
Fishes
Walleye pollock (Theragra chalcogramma). In a
survey of demersal fishes of the eastern Bering Sea
conducted by Pereyra et al. (1976), walleye pollock
was the most abundant species encountered.
Young British Columbia walleye pollock, from 4 to
22 mm standard length, fed on copepods and their
eggs (Barraclough 1967); adults fed on shrimps,
sand lance, and herring (Hart 1949). Armstrong and
Winslow (1968) also reported that walleye pollock
off British Columbia fed on young pink, chum, and
coho salmon.
Suyehiro (1942) reported small shrimps, benthic
amphipods (Anonyx spp.), euphausiids, and copepods
in the stomachs of pollock from the Aleutians. Mito
(1974) examined the food of walleye pollock from
the southeastern Bering Sea and concluded that the
most important prey organisms, in terms of percen-
tage of total food weight, were Euphausiacea (Thysa-
noessa inermis) and 0-year-old walleye pollock. The
pelagic amphipod, Parathemisto pacifica, and the
pink shrimp, Pandalus borealis, were also important
* Sponges, anemones, and tunicates are abundant in the
Bering Sea: Feder and Jewett 1978, 1980; pelagic groups
such as Scyphomedusae are abundant and contribute larvae.
prey. Andriyashev (1964) listed mysids and amphi-
pods as the major foods of Bering Sea waUeye pollock,
with the snow crab Chionoecetes opilio also present.
He also reports that pollock from Peter the Great
Bay and Sakhalin Island feed on surf smelt and
capelin in the spring and shift to planktonic crus-
taceans in the summer.
Smith et al. (1978) examined walleye pollock
from the northeastern Gulf of Alaska and the south-
eastern Bering Sea. Stomachs of GuLf of Alaska
fish (x standard length = 344 ± 84 mm) as well as
Bering Sea fish (x standard length = 270 ± 145 mm)
mainly contained euphausiids. Majid crabs, hyperiid
amphipods, and fishes were also taken. Walleye
pollock (95-145 mm standard length) from lower
Cook Inlet mainly contained shrimps, specifically
crangonid and pandalid species (Feder, unpub. data).
PoUock examined (22-358 mm standard length)
from Prince William Sound, Alaska, by Feder and
Paul (1977) fed primarily on the pelagic amphipod,
Parathemisto libellula, and the pink shrimp , Pandalus
borealis.
Since the walleye pollock is the most abundant
fish species in the eastern Bering Sea, it is also one of
the most commonly consumed fishes. Predators
include walleye pollock. Pacific cod, great sculpin,
sablefish. Pacific halibut, Greenland halibut, flathead
sole, arrowtooth flounder, murres, harbor seal,
ribbon seal, and humans.
Pacific cod (Gadus macrocephalus). Food habits
of Pacific cod in the Bering Sea are moderately well
known. Suyehiro (1942) examined the food of
Pacific cod captured in Bristol Bay. Fish foods were
walleye pollock, flatfishes, and small unidenti-
fied fishes. Invertebrates used as food included poly-
chaete worms, a clam (Yoldia sp.), shrimps, hermit
crabs, true crabs (Hyas and Pinnixa), and amphipods.
Krivobok and Tarkovskaya (1964) reported that cod
from the southeastern Bering Sea contained "large
numbers" of pollock, herring, smelt (Osmeridae),
capelin, flatfishes, eelpouts, crabs, shrimps, octopi,
snails, and clams. No quantitative data were given.
Mito (1974) examined Pacific cod from the south-
eastern Bering Sea and found that cod less than 450
mm long fed mainly on decapod crustaceans such as
Chionoecetes opilio, Pandalus borealis, and Crangon
dalli, and 0-year-old Theragra chalcogramma. Pacific
cod longer than 501 mm fed almost exclusively on
pollock one year old or older.
Pink shrimp (P. borealis) was the dominant food of
adult Pacific cod from the southeastern Bering Sea;
walleye pollock, amphipods, snow crabs, and miscel-
laneous invertebrates were also important prey
(Feder and Jewett 1980).
Feeding interactions with emphasis on the benthos 1239
Adult Pacific cod from lower Cook Inlet preyed
mainly on snow crab, crangonid shrimps, and fishes
(Feder, unpub. data).
Jewett (1978) presented data on stomach contents
of adult Pacific cod caught in summer months near
Kodiak, Alaska. The most important food categories
were fishes, crabs, shrimps, and amphipods, in de-
creasing order of occurrence. The fish most frequent-
ly eaten was the walleye pollock; Pacific sand lance
(Ammodytes hexapterus) and flatfishes also contrib-
uted frequently to cod diet. The snow crab Chio-
noecetes bairdi occurred most frequently, appearing
in almost 40 percent of the stomachs examined.
Little year-to-year variation was found in the diet of
Pacific cod.
Pacific cod are mainly preyed upon by sablefish,
Greenland halibut, Pacific halibut, arrowtooth floun-
der, harbor seal, and humans, although they are not
a dominant prey of any predator.
Sculp ins (Myoxocephalus spp.). Little feeding
information on the sculpins, Myoxocephalus spp.,
has been reported from the Bering Sea. Mito (1974)
examined the stomach contents of Myoxocephalus
polyacanthocephalus from the southeastern Bering
Sea and determined that the dominant prey, in terms
of percentage of food weight, was Chionoecetes
opilio. Walleye poUock, miscellaneous fishes, cephalo-
pods, and a spider crab (Hyas coarctatus) were
next in importance. Polychaetes and benthic amphi-
pods (Anonyx spp.) were rarely taken. Examinations
of Myoxocephalus by Feder and Jewett (1980)
confirmed reports by other investigators that Myoxo-
cephalus eat mainly crabs and fishes.
Food of Myoxocephalus spp. (M. polyacantho-
cephalus and M. joak) was examined off Kodiak
Island in the summers of 1973-75 (Jewett and Powell
1979). The dominant food groups were crabs and
fishes with the snow crab the most frequently
consumed species. The fishes were dominated by
Cottidae. Myoxocephalus polyacanthocephalus from
lower Cook Inlet primarily ate snow crab, a spider
crab (Hyas lyratus), and shrimp (Crangon dalli)
(Feder, unpub. data).
Myoxocephalus spp. appear to have few predators.
However, harbor, spotted, and ringed seals have been
reported to feed on sculpins, and it is assumed that
Myoxocephalus is included.
Alaska plaice (Pleuronectes quadrituberculatus).
Skalkin (1963) reported that the major benthic food
groups for southeastern Bering Sea Alaska plaice
were polychaetes, mollusks, and crustaceans (amphi-
pods and hermit crabs), and these prey were present
in approximately equal numbers. Not all of the food
groups were found in stomach contents at any one
time; the diet consisted rather of any one of the
groups or a combination of two. No single poly-
chaete species dominated in weight or incidence of
occurrence. When mollusks comprised a considerable
proportion of the diet, either the Greenland cockle
(Serripes groenlandicus) or some combination of
three other species of bivalves— yo/d /a hyperborea,
Y. johanni, and Liocyma (= Gomphina) fluctuosa—
occurred in stomachs. Amphipods were the main
crustaceans taken.
Kulichkova (1955) examined the food of Alaska
plaice from a shallow portion of the northwest
Kamchatka coast and determined that the clam
Siliqua media was the dominant prey, in frequency
of occurrence and index of fullness.
Mineva (1964) reported that Alaska plaice do not
feed in winter in the southeastern Bering Sea. Alaska
plaice examined by Feder and Jewett (1980) in the
southeastern Bering Sea during the late winter and
early spring (28 March to 4 June 1976) showed little
feeding activity. No food item dominated.
Pacific halibut (Hippoglossus stenolepis). Mito
(1974) examined the stomach contents of Pacific
halibut from the southeastern Bering Sea. Small
fish (341-600 mm) fed mainly on Pacific sandfish
(Trichodon trichodon) and the wattled eelpout
(Lycodes palearis), while larger fish (601-2,040 mm)
fed mainly on walleye pollock one year old or more.
Novikov (1964) has reported on Pacific halibut food
habits from the southeastern Bering Sea (see also
review in Pereyra et al. 1976 for tabulation of
Novikov's data). Small hahbut (30 cm or less) fed
primarily on pink shrimp, king crab, and snow
crab; medium-sized fish (30-60 cm) shifted to a
largely fish diet. Fish larger than 60 cm fed pre-
dominantly on other fishes. Among flounders,
yellowfin sole was the halibut's principal prey.
Smith et al. (1978) presented previously unpub-
lished International Pacific Halibut Commission data
on food of juvenile halibut from the southeastern
Bering Sea. Major food organisms, in percent fre-
quency of occurrence, were unidentified fishes (25
percent), sand lance (15 percent), and crabs (6
percent).
Greenland halibut (Reinhardtius hippoglossoides).
The Greenland halibut appears to prey strictly on
fishes. All Greenland halibut examined by Feder
and Jewett (1980) in the southeastern Bering Sea
contained fishes; gadids and unidentified fishes were
the most important prey.
Mito (1974) examined the food of Greenland hali-
but in the southeastern Bering Sea. He found that
the main prey were walleye pollock one year old or
more. Other food included Pacific herring and arrow-
tooth flounder. Mikawa (1963) examined stomach
contents of Greenland halibut from a variety of areas
1240 Benthic biology
extending from Unimak Island to coastal Japan. In
the central and eastern Bering Sea most of the stom-
achs examined were empty. Pollock, unidentified
fishes, and squids predominated in the stomachs
which did contain food. Mikawa found that feeding
intensity peaked in June-September and then de-
clined; the lowest incidence of feeding was observed
in January through May. Of the Greenland halibut
examined by Feder and Jewett (1980) (March-
June), 54 percent had empty stomachs. Those
which were feeding were primarily eating unidenti-
fied fishes, walleye pollock, and unidentified gadids.
The stomachs of Reinhardtius hippoglossoides
from the Bering Sea were examined by Smith et al.
(1978) from April to May; 44 percent of the fish
contained food. Fishes were the most important
component of the diet of R. hippoglossoides; only
one specimen had consumed crustaceans. Of the
identifiable fishes in the stomachs the walleye pollock
occurred most frequently. Other prey items were
capelin (Mallotus uillosus) and cottids.
Smith et al. (1978) suggest that i2. hippoglossoides
may reduce its feeding activity during winter months
and resume feeding in late May. Similar seasonal
changes in feeding habits have been observed for
other flatfishes in the Bering Sea (Skalkin 1963).
Arrowtooth flounder (Atheresthes stomias).
Shuntov (1965) reported that the walleye pollock
was the principal food of the arrowtooth flounder
in the Bering Sea. Mito (1974) examined the food
of arrowtooth flounder from the southeastern Bering
Sea, and found the dominant prey to be juvenile
walleye pollock with pink shrimp, squids, and
euphausiids (Thysanoessa spp.) also consumed.
Smith et al. (1978) examined this species from the
northeast Gulf of Alaska. Crustaceans and fishes
were most frequently eaten; polychaetes, mollusks,
and echinoderms were rarely eaten. Of the crusta-
ceans, decapods were most often taken, euphausiids
next most often. However, euphausiids were more
important by number and volume. In descending
order of frequency of occurrence, members of the
fish families Osmeridae, Gadidae, and Zoarcidae
were the most common teleostean prey. Repre-
sentatives of the families Clupeidae, Cottidae,
Stichaeidae, and Pleuronectidae were also found
among the stomach contents.
Greenland halibut have been reported to prey upon
arrowtooth flounders (Nito 1974).
Starry flounder (Platichthys stellatus). Food of
starry flounder from the southeastern Bering Sea
was examined by Skalkin (1963). He reported that
a polychaete (Travisia forhesii), bivalves (Siliqua sp.
and Tellina lutea), and the sand lance (Ammodytes
hexapterus) were among the stomach contents,
although no order of dominance was specified.
Jewett and Feder (1980) examined the food of
adult starry flounder in the northeastern Bering
Sea and southeastern Chukchi Sea in September and
found major differences between food consumed in
three regions. The dominant prey organisms of
starry flounder from the Norton Sound region were
a protobranch clam (Yoldia hyperborea), a brittle
star (Diamphiodia craterodmeta), and a sand dollar
(Echinarachnius parma). Fish from the Port Clarence
area mainly consumed Y. hyperborea and D. crater-
odmeta. A proboscis worm (Echiurus echiurus
alaskensis) and a prickleback fish (Lumpenus fabricii)
were the major prey of fish from the southeastern
Chukchi Sea.
Rex sole (Glyptocephalus zachirus). Mito (1974)
examined the stomach contents of rex sole from the
southeastern Bering Sea, and determined that the
main foods consisted of polychaetes (mainly Lum-
brinereis sp.) and gammarid amphipods. Mineva
(1964) presented some data on feeding intensity,
but he did not mention specific food items.
Smith et al. (1978) examined rex sole from the
northeastern GuLf of Alaska. Ten families of poly-
chaetes contributed most of the food consumed.
Pelecypods, cumaceans, amphipods, euphausiids, and
decapods (especially Pandalus borealis and Chionoe-
cetes bairdi) were also common in the diet. The few
rex sole examined by Feder and Jewett (1980)
in the southeastern Bering Sea contained prey similar
to that found by Smith et al. (1978) in the gulf,
i.e., amphipods and polychaetes.
Rock sole (Lepidopsetta bilineata). Skalkin (1963)
and Shubnikov and Lisovenko (1964) reported that
polychaetes were most important in the diet of
Bering Sea rock sole, mollusks (bivalves) and crus-
taceans (mainly shrimp) next most important. Mito
(1974) examined the food of rock sole from the
southeastern Bering Sea and concluded that a brittle
star (Ophiura sp.) was the most frequent prey;
polychaetes (Lumbrinereis sp. and Onuphis sp.),
gammarid amphipods, and snow crab (Chionoecetes
opilio) were also frequently taken. Of the rock sole
examined by Smith et al. (1978), 48 percent had
empty stomachs. Eleven families of polychaetes
contributed most of the food consumed. Crusta-
ceans, pelecypods (Nuculana and Serripes), ophiu-
roids, and fishes were also important.
Kravitz et al. (1976) found that rock sole in
Oregon waters fed mainly on ophiuroids. Feeding
was reduced during the winter and was most intense
in Jime and July.
Feeding interactions with emphasis on the benthos 1241
Yellowfin sole (Limanda aspera). In a demersal
fish survey of the eastern Bering Sea conducted by
Pereyra et al. (1976), yellowfin sole was the second
most abundant fish species encountered. Kulichkova
(1955) examined the food of yellowfin sole from
shallow waters in the northwest Kamchatka coast
and determined that the clam Siliqua media and
fishes contributed 41 and 59 percent of the fullness
index, respectively. Siliqua media occurred in 66 per-
cent of the fish examined. Feeding data included in
Andriyashev (1964) indicated that Limanda aspera
feeds mainly on polychaetes, pelecypods, and ophiu-
roids in northern Russian waters. Skalkin (1963)
reported approximately 50 different taxa as food of
the yellowfin sole in the Bering Sea. He divided these
taxa into three groups. The first group was high
in both frequency of occurrence and numbers. This
group included benthic amphipods, mysids, euphau-
siids, two bivalves (Liocyma fluctuosa and Clino-
cardium ciliatum), and an ascidian (Molgula sp.).
A second group, the members of which occurred
frequently but in smaller numbers, included the
proboscis worm (Echiurus echiurus), shrimps
(Crangon dalli, Pandalus borealis), and clams (Yoldia
johanni, Y. hyperborea, Nuculana fossa). A third
group, containing the Greenland cockle (Serripes
groenlandicus) and a brittle star (Ophiura sarsi),
consisted of forms which commonly occurred in
yellowfin sole stomachs but always in fragmented
condition. Skalkin (1963) suggested that yellowfin
feeding habits vary with geographic subregion and
depth in the southeastern Bering Sea. For instance,
he states that mysids and euphausiids predominate in
the diet in the northeastern sector (southwest of Cape
Newenham and Kuskokwim Bay), whereas other
crustacean species begin to dominate further to the
southwest and to the northwest. He cites a predomi-
nance of polychaetes in fish from depths of 30 to
60 m, moUusks from 65 to 80 m, and O. sarsi from
depths greater than 80 m.
Marked seasonality of feeding is suggested by
Skalkin (1963). YeUowfin sole apparently do not
feed until late April on the wintering grounds north
of Unimak Island. Feeding intensity is low in May as
fish migrate toward shallow water and high in July
in the southeastern Bering Sea; it falls off during the
fall as yellowfin populations begin moving back
down to deeper water. These conclusions were based
on an analysis of fish captured from July to Septem-
ber 1958 and from April to June 1960.
One of the major predators on yellowfin sole is
the Pacific halibut (Novikov 1964).
Yellowfin sole is the dominant flatfish species
taken by foreign fishermen in the eastern Bering Sea.
Most of the fishing is conducted approximately mid-
way between the Pribilof Islands and Kuskokwim
Bay (Smith and Hadley 1979).
Flathead sole (Hippoglossoides elassodon). Mineva
(1964) examined flathead sole from the southeastern
Bering Sea, and found the stomach contents to
consist mainly, in order of decreasing frequency of
occurrence, of ophiuroids, shrimps, benthic amphi-
pods, fish remains, and moUusks, especially the proto-
branch clams Yoldia spp. Skalkin (1963) and Mito
(1974) reported that the most common food species
in flathead sole from the southeastern Bering Sea
were a brittle star (Ophiura sarsi) and the pink
shrimp (Pandalus borealis). Skalkin (1963) also
found that as flathead sole migrate from the southern
portion of the Bering Sea to shallower waters echino-
derms decreased in importeince; Pandalus borealis
was replaced by planktonic Crustacea (hyperiid
amphipods and euphausiids) and chaetognaths
(Sagitta spp.). Mito (1974) found Chionoecetes
opilio and juvenile walleye pollock among stomach
contents.
Smith et al. (1978) examined flathead sole from
the Gulf of Alaska and the Bering Sea. Euphausiids
(probably all Thysanoessa spp.) and a brittle star
(Ophiura sarsi) constituted most of the diet of the
samples from the Gulf of Alaska. The Bering Sea
data suggest that the pink shrimp was the most
important spring prey; mysids, amphipods, and
Ophiura sarsi dominated summer feeding. Crangonid
shrimps and juvenile pollock were the most impor-
tant autumn prey in the Bering Sea.
Marine mammals
Pacific walrus (Odobenus rosmarus diuergens).
Fay et al. (1977) estimated that the present popula-
tion of 150-200 thousand walrus consumes about
3.3-4.4 million mt of benthic organisms per year,
or about 1 percent of the total available food. The
most extensive information on the food of this
mammal was obtained from the northern Bering Sea/
Bering Strait by Fay et al. (1977). In that study
identifiable prey items included representatives of
10 phyla and at least 45 genera. These included 5
polychaetous annelids, 2 sipunculids, 1 echiuroid,
1 priapulid, 12 crustaceans, 17 mollusks, 4 holo-
thurian echinoderms, 2 ascidians, and 1 mammal.
Of the identified food items, the bivalve mollusks
Hiatella, Mya, Spisula, Clinocardium, and Serripes
comprised more than 90 percent of the total mean
numerical density, more than 80 percent of the
total volume, and more than 85 percent of the
organic carbon (Table 69-1).
Harbor seal (Phoca vitulina richardsi). There is
little information available on the foods of the harbor
1242 Benthic biology
seal in the Bering Sea. Harbor seal from Aleutian
Island waters prey mainly on pandalid shrimps,
octopus, and pollock, although mysids, crangonid
shrimps. Pacific cod, and sculpins are also taken
(Lowry et al. 1979). Octopus, Atka mackerel, and
greenling were the major food items found in harbor
seal collected at Amchitka Island (Wilke 1957,
Kenyon 1965). Similarly, a mixture of fishes, cepha-
lopods, and shrimps has been reported in the diet of
harbor seal from the Komandorsky Islands (Marakov
1968) and Kuril Islands (Panina 1966). The only
prey found in a harbor seal from southeastern Bristol
Bay was capelin (Lowry et al. 1979).
Spotted seal (Phoca uitulina largha). The food
habits of spotted and harbor seals are similar along
the Bering Sea coast during the summer. In the
summer-fall period spotted seal in the coastal zone
of the Seward Peninsula feed on herring, saffron cod,
smelt, sculpins, and occasionally shrimps (Lowry,
Frost, and Burns, unpub.). Spotted seal from
Nunivak Island contained a variety of nearshore
fishes and shrimps, i.e., greenlings, herring, sculpins,
and crangonid shrimps (Lowry et al. 1979). Similar
results have been reported for the Komandorsky
Islands (Barabash-Nikiforov 1936) and Robben
Island (Nikolaev and Skalkin 1975). Spotted seal
taken on the pack ice of the Okhotsk Sea and in a
region northwest of the Pribilof Islands mainly
contained pollock (Wilke 1954, Fedoseev and
Bukhtiyarov 1972, Lowry et al. 1979). Goltsev
(1971) reported that a number of different fishes and
shrimps were consumed by spotted seal during the
spring in Karaginski Bay and the Gulf of Anadyr.
Lownry et al. (1979) found that during March and
April in Bristol Bay capelin was the only food taken
by spotted seal.
Ringed seal (Phoca hispida). Ringed seal stomachs
examined in 1977 by Lowry (unpub.) from several
locations in Alaskan arctic and subarctic waters
contained a variety of prey. The dominant prey at
Nome and Wales was saffron cod (Eleginus gracilus).
The dominant prey near Barrow was euphausiids
(Thysanoessa spp.). In the central Beaufort Sea
hyperiid amphipods (Parathemisto libellula)
accounted for most of the stomach contents. Ringed
seal near St. Lawrence Island contained mostly
shrimp (Eualus gaimardii, E. fabricii, and Pandalus
goniurus) and lesser amounts of mysids (Mysis
littoralis and Neomysis rayii), a hyperiid amphipod
(P. libelulla), and gammarid amphipods (mostly
Anonyx nugax). Few fishes were found in their diet
near St. Lawrence Island. At little Diomede Island,
Arctic cod (Boreogadus saida) and shrimps (E.
gaimardii, P. goniurus, and Lebbeus polaris) were of
equal importance in the diet. A considerable volume
of gammarid amphipods (mainly A. nugax) was also
eaten. The main foods of ringed seal from
Shishmaref were saffron cod, Arctic cod, and shrimps
(Crangon septemspinosa, E. gaimardii, and P.
goniurus).
Ringed seal examined in earUer studies from the
Okhotsk Sea (Fedoseev 1965), eastern Chukchi Sea
(Johnson et al. 1966), Bering Strait (Kenyon 1962),
and Nunivak Island (Lowry et al. 1979) also fed
on similar items, i.e., zooplankton, crangonid shrimps,
saffron cod, Arctic cod, herring smelt, and sculpins.
Ribbon seal (Phoca fasciata). Foods of ribbon
seals vary regionally. Stomachs of ribbon seal from
an area northwest of the Pribilof Islands in March
and April contained mainly fishes (Lowry et al.
1979). PoUock, eelpout, and capelin were the most
important species, although flatfishes were also
found. The only invertebrate present was octopus.
Similar results were reported for ribbon seal in the
Okhotsk Sea by Fedoseev and Bukhtiyarov (1972).
However, Shustov (1967) examined stomachs from
the northern Bering Sea and in the 3 percent of the
stomachs containing food, crustaceans (shrimps,
crabs, and mysids) were more common than fishes.
Bearded seal (Erignathus barbatus). The diet of
the bearded seal is different from those of other
phocid seals in the Bering Sea, in that fishes are rarely
taken. The stomach contents of bearded seal from the
southeastern Bering Sea mainly consisted of snow
crab (Chionoecetes opilio), crangonid shrimps (Argis
spp. and Sclerocrangon boreas), and spider crabs
(Hyas spp.) (Lov^ry et al. 1979). Mollusks, specifi-
cally the Greenland cockle (Serripes groenlandicus)
and less important gastropods (Buccinum spp. and
Polinices spp.) have also been reported as important
prey of bearded seal in selected regions of the Bering
Sea in summer months (Lowry et al. 1979). Kosygin
(1971) found crustaceans, mostly snow crab, to be
the primary food of this seal in the Bering Sea,
although snails, polychaetes, and demersal fishes were
also taken (Table 69-1).
FOOD DYNAMICS
The Bering Sea food webs presented in Figs. 69-1
to 69-6 show qualitative predator-prey linkages of
dominant or ecologically important taxa, or both.
Organisms included in the generalized food web (Fig.
61-1) are presented in groupings of convenience.
Thus, taxa are generally found either in groups that
include pelagic or benthic organisms or in major
taxonomic categories— invertebrates, fishes, birds, and
mammals.
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1243
1244 Benthic biology
The most abundant macrozooplankters of the
eastern Bering Sea (copepods, mysids, and euphau-
siids) are primarily grazers (Alexander and Cooney
1979; Cooney, Chapter 57, this volume). These small
crustaceans are the dominant food of walleye pollock,
capelin. Pacific ocean perch, and Pacific salmon
(mainly the sockeye salmon), as well as occurring
frequently in the diets of a variety of other fishes, sea
birds, and whales (Fay et al. 1977, Sanger and Baird
1977a, Bakkala and Smith 1978, Iverson et al. 1979,
Feder and Jewett 1980).
Among the nearly 300 species of fishes in the
Bering Sea (Wilimovsky 1974), the walleye pollock
is the dominant species. Pollock are preyed upon by
a wide variety of organisms, including fishes, sea
birds, marine mammals, and humans. Mito (1974)
analyzed the feeding relationships in the Bering Sea
demersal fish community, and found that the pollock
was an important trophic link there. It was identified
as a key food for 63 demersal fishes and, in turn,
consumed a total of 58 different food organisms,
mainly macrozooplankton.
A diverse group of benthic invertebrates is found
on the shelf of the eastern Bering Sea, living at the
sediment surface (epifauna) or within the sediment
(infauna) (see appropriate chapters in this section).
The feeding regimes of these invertebrates, as in
most benthic systems, are varied. For example,
suspension feeding is practiced by some polychaetous
annelids (e.g., Sabellidae, Serpulidae), many species
of clams, bryozoans, barnacles, and tunicates.
Deposit feeding is the method of echiuroids (Echiurus),
many polychaetous annelids (e.g., Maldanidae,
Capitellidae), some species of clams (e.g., Nucula,
Nuculana), and brittle stars {e.g., Diamphiodia spp.).
The presence of sediment in the gut of epifaunal
species generally considered to be predators (e.g.,
pandalid and crangonid shrimps, snow crab, and
hermit crabs), suggests that these species may utilize
organic constituents associated with sediments
as a supplemental carbon source (Feder et al. 1980b,
Rice 1980, Rice etal. 1980). Furthermore, suspension
feeders (e.g., cockles and tellinid clams) utilize
detritus and associated bacteria when bottom mate-
rials are resuspended by storms in mid-shelf and
inner-front zones. (See papers reviewing utilization
of detritus, bacteria, and organically enriched sedi-
ments by benthic invertebrates: e.g.. Baker and
Bradnam 1976, Tenore 1977, Fenchel and J)6rgensen
1977.) Predatory benthic invertebrates are common
in the eastern Bering Sea. Some groups such as
gastropods (Natica, Polinices), crustaceans (pandalid
and crangonid shrimps, king and snow crabs, hermit
crabs), and echinoderms (Ophiura, Asterias, Leptas-
terias) represent major predators on other benthic
invertebrates such as polychaetes, small crustaceans,
and bivalve mollusks (Feder and Jewett 1981;
Feder et al. 1980b; Feder, unpub. data).
The major bottomfish components of the Bering
Sea are the sculpins (Cottidae),blennies (Stichaeidae),
eelpouts (Zoarcidae), snailfishes (Cyclopteridae),
cods (Gadidae), and flatfishes (Pleuronectidae).
Most species in these fish groups feed on epifaunal
or infaunal organisms, or both, in the Bering Sea
and elsewhere (Pereyra et al. 1976, Jewett 1978,
Jewett and Powell 1979, Feder and Jewett 1980).
Sculpins and Pacific cod forage intensively on surface-
dwelling species such as shrimps and crabs, whereas
many species of flatfishes (rex sole, yellowfin sole,
Alaska plaice, rock sole, flathead sole) feed primarily
on infauna (e.g., polychaetous annelids, clams, brittle
stars).
Opportunistic feeding seems to be the most com-
mon mode of most bottom-feeding fishes as well as
predatory invertebrates and marine mammals. Thus,
in the Bering Sea, the flathead sole feeds on clams as
well as crabs; snow crabs feed on polychaetes, soft-shell
clams, brittle stars, and hermit crabs; red king crab on
polychaetes, clams, cockles, barnacles, hermit crabs,
sand dollars, sea urchins, and brittle stars; and sea
stars on clams and cockles; bearded seal take clams or
crabs; walrus dig for clams but also eat a variety of
epifaunal species.
Approximately 132 species of marine or marine-
oriented birds occur in the eastern Bering Sea or its
adjacent estuarine or intertidal habitats (Sanger and
Baird 1977a). Sanger and Baird (1977b) give
24.9 X 10^ birds as a conservative estimate of the
abundance of dominant sea birds in the eastern
Bering Sea. These birds take a variety of prey and,
depending on the species, feed (1) at or just beneath
the water surface (most gulls— omnivores and scav-
engers that mainly eat fishes and euphausiids), (2) in
the upper few meters (Short-tailed Shearwaters,
which mainly feed on euphausiids and capelin), (3) at
mid-depths (puffins, some other alcids, which mainly
eat crustaceans, cephalopods, and schooling fishes),
or (4) from mid-depths to the bottom (murres,
which feed on schooling fishes; cormorants, which
take flatfishes and shrimp; and sea ducks, which
take benthic invertebrates) (Fig. 69-1).
The marine mammal fauna of the Bering Sea
comprises some 25 species, most of which are tran-
sient, remaining about half the year there and half
farther to the north or to the south (Fay 1974).
This fauna is estimated to be the equivalent of a
full-time resident population of about 1.5 X 10^
with a combined total biomass of about 4.5 X
Feeding interactions with emphasis on the benthos 1245
10^ mt. These marine mammals have been estimated
to consume about 9 to 10 X 10^ mt of nekton and a
diversity of benthic species annually in the Bering
Sea, about four times the annual catch taken by the
commercial fisheries (Fig. 69-1).
GENERAL DISCUSSION
The Bering Sea, specifically the southeastern
section, contains some of the world's largest standing
stocks of commercially exploitable shellfishes and fin-
fishes (Pereyra et al. 1976), and many representatives
of these groups obtain a large proportion of their
diet from the benthos. Neiman (1963) and Alton
(1974) discuss the proportion of benthos available
as food to bottom-feeding species in various regions
of the Bering Sea. The proportion of food benthos
is highest in the northwestern (Gulf of Anadyr)
and southeastern shelf regions of the Bering Sea and
lowest on the southwestern shelf. The benthos of
the northeastern Bering Sea, which accounts for
86 percent of the total benthos on the eastern shelf,
\\d& comparatively reduced numbers of demersal
fishes (Neiman 1963) presumably due to low-temper-
ature barriers normally present. Furthermore, of the
total estimated food benthos on the eastern Bering
Sea shelf (3.2 X lO'^ mt), 77 percent is generally
inaccessible to bottom fishes because of low tempera-
tures typically prevailing in most of the Bering Sea
(Neiman 1963, Alton 1974). In the southeastern
Bering Sea, where 23 percent of the food benthos
of the eastern shelf is found, bottom fishes have
year-round access to the food resources. From this
sector of the Bering Sea over 10.2 X lO'* mt of crabs
and 2 X 10^ mt of bottom fishes, which feed to a
great extent on the benthos, are removed annually
(J. Reeves, NMFS and K. Griffin, ADF&G, personal
communications, and Pereyra et al. 1976).
Most of the crabs and bottom fishes of the south-
eastern Bering Sea shelf feed on the nutrient-enriched
upper slope during winter, and move into shallower
and warmer waters for intensive feeding and spawning
in summer. However, as discussed above, demersal
fishes exploit the colder northern portions of the
Bering Sea shelf only during warm years (Hood and
Kelley 1974, Jewett and Feder 1980). The tempera-
ture-related differences in distribution of crabs and
bottom fishes are reflected by catch statistics which
demonstrate that the southeastern shelf, unlike
the colder northeastern portion of the shelf, is a
major fishing area for these organisms. In fact, the
effect of intensive predation by the large populations
of crabs and bottom fishes on the southern shelf may
be responsible for the low standing stock of the
total benthos there (14 percent of the total benthos
of the eastern Bering Sea) in contrast to that of the
northeastern shelf (86 percent) (Neiman 1963).
Kulichkova (1955) compared the diets of red king
crab, Alaska plaice, and yellowfin sole from the
coastal zone of western Kamchatka, and concluded
that these species are actively competing for the
same prey resource, i.e., the clam Siliqua media.
Distribution and relative abundance data in the south-
eastern Bering Sea reveal that king crab, yellowfin
sole, and rock sole have similair distributions and
areas of biomass dominance (Pereyra et al. 1976).
Since these predators take similar prey elsewhere,
it may be assumed that they also compete for food
in the southeastern Bering Sea. However, such
competition takes place only when seasonal migra-
tions of these species result in overlapping distribu-
tions. Foreign trawl fisheries data (Smith and Hadley
1979) show that the major area for yellowfin sole
catches from July through December 1978 was
approximately 150 km east by northeast of the
Pribilof Islands. However, catches during the re-
mainder of the year were farther south near major
king crab populations (see Fig. 69-10).
It is apparent that large, bottom-feeding species
in the Bering Sea are feeding on slow-growing poly-
chaetous annelids, snails, and clams (Feder and
Jewett 1980; McDonald et al., Chapter 66, this
volume). However, zooplankters probably grow
rapidly in the nutrient-rich water at the shelf edge
and provide additional food resources at the shelf
edge and on the shelf as they are transported shore-
ward by water movements. Furthermore, periodic
carbon enrichment of the benthos at mid-shelf areas
(40-100 m) of the southeastern Bering Sea
(Alexander and Cooney 1979; Iverson et al. 1979,
Cooney, Chapter 57, this volume) also results in
enhancement of food resources on the bottom and
may also be responsible for more frequent recruit-
ment successes there. Such successes are suggested
by the presence of Isirge numbers of bivalve moUusks
of similar age (Stoker 1978; K. Haflinger, unpub.
observations; Stoker, Chapter 62, this volume) in
some regions of the mid-shelf (Fig. 68-7). For
example, nearly 3,000 Clinocardium ciliatum/m^
of similar age are reported by Feder et al. (1980a)
and Haflinger (unpub.) at one mid-shelf station (see
also Stoker, Chapter 62, Haflinger, Chapter 63, and
McDonald et al.. Chapter 66, this volume for further
comments on clam densities and biomass on the
Bering Sea shelf). Dense populations of deposit-
feeding clams and high densities and biomass of other
infauna (Fig. 69-8; Haflinger, Chapter 63, this volume)
1246 Benthic biology
180°
175^
170°
165°
160°
155°
1 1 I \ I T
Figure 69-7. Quantitative distribution of dams (28 species) taken by van Veen grab in the southeastern Bering Sea, 1975-76.
on the mid-shelf indicate long-term biological re-
sponses to unusual amounts of carbon. Furthermore,
the large biomass of epifaunal predators (e.g., snow
crabs, red king crab) (Figs. 69-9 and 69-10), as well as
a general increase in epifaunal biomass (composed of
a mixed group of feeding types that would benefit
from increased carbon influx; Fig. 69-11) also reflects
carbon enrichment of the mid-shelf.
Bivalve mollusks are widely dispersed over the
Bering Sea shelf and, as indicated above, are abun-
dant on the mid-shelf. They are the most commonly
consumed prey in the Bering Sea, and represent
resources for which crabs, sea stars, bottom fishes,
bearded seal, and walrus may compete (Table 69-1).
King crabs consume hard-shell (Clinocardium, Cyclo-
cardia, Chlamys, Serripes, and Spisula) as well as
soft-shell (Nucula, Nuculana, Yoldia, Macoma,
Siliqua, and Tellina) bivalves. Reduced numbers of
clams are apparent at stations heavily populated by
red king crab (Figs. 69-7 and 69-10). However, one
common bivalve, the small soft-shell clam Nucula
tenuis (Fig. 69-12), is rarely consumed by the king
crab. Clinocardium, a preferred food of red king
crab, is more common immediately north of king
crab foraging areas (Fig. 69-13) (McDonald et al..
Chapter 66, this volume). Although snow crabs prey
Feeding interactions with emphasis on the benthos 1247
I
180°
175'
170°
165°
160'
155'^
175°
170°
165'
160°
Figure 69-8. Quantitative distribution of total infauna talcen by van Veen grab in tiie southeastern Bering Sea, 1975-76.
on small, soft-shell genera such as Nucula, Nuculana,
Yoldia, Macoma, and Axinopsida, they do not
generally feed on bivalves as intensively as red king
crab in the Bering Sea (Feder and Jewett 1980). And
yet high densities of Chionoecetes opilio in the
southeastern Bering Sea occur where bivalves are
common (Figs. 69-7 and 69-9). The data (Feder and
Jewett 1980; Jewett and Feder, Chapter 65, this
volume) indicate that foraging areas of C. opilio and
P. camtschatica, in general, do not overlap (Figs. 69-9
and 69-10); thus predation pressure on bivalves they
both use as food is reduced.
Sea stars and flatfishes prey on at least ten differ-
ent bivalve species, of which more than half are
also consumed by king or snow crabs, or both (Table
69-1; see adso McDonald et al.. Chapter 66, this
volume for a discussion of clam distribution, abun-
dance, and age as influenced by benthic predators).
Hatanaka and Kosaka (1958) demonstrated that
sea stars and bottom fishes compete for bivalve
resources in Sendai Bay, Japan. They estimated
that food (primarily clams) consumed annually
by the sea star Asterias amurensis amounted to
8 X 10^ mt, approximating the annual consumption
(10 X 10^ mt) of food (primarily clams) taken by
bottom fishes. In the northern portion of the Bering
1248 Benthic biology
180°
175°
170°
165°
160°
155°
Figure 69-9. Quantitative distribution of the snow crab Chionoecetes opilio in tlie southeastern Bering Sea, 1975-76.
Sea, where low water temperatures prevail, sea
stars are the dominant macro benthic predators (Feder
and Jewett 1978). Neiman (1963) and Moiseev
(1964) suggest that annual fluctuation in water
temperature, rather than availability of food, may be
responsible for the maximum northern distribution of
many benthophagic flatfishes. Thus, in years when
seawater temperatures rise sufficiently, flatfish
populations invade the rich northern waters and
actively compete with sea stars for bivalve resources.
Such competition between starry flounders and sea
stars in the northern Bering Sea is discussed by
Jewett and Feder (1980) (see also Feder and Jewett,
1978).
The Pacific walrus (Odobenus rosmarus divergens)
is perhaps the greatest bivalve predator in the eastern
Bering Sea (Fay, Chapter 48, this volume). Stoker
(1977) estimated that walrus take 1.1 X 10* mt
of bivalves annually in the Bristol Bay area alone.
Further competition for Bering Sea clam resources
may occur if commercial clam harvesting begins
(see Hughes and Nelson 1979; Hughes and Bourne,
Chapter 67, this volume for a discussion of a potential
clam fishery for the Bering Sea). Target species for
this proposed fishery would be the Alaska surf clam,
Spisula polynyma, also common in the diet of Pacific
walrus. The bearded seal (Erignathus barbatus), a
species of the northern Bering Sea, also preys on
Feeding interactions with emphasis on the benthos 1249
180°
175°
170°
165°
160°
155°
175'
170
165°
160°
Figure 69-10. Quantitative distribution of the king crab Paralithodes camtschatica in the southeastern Bering Sea, 1975-76.
bivalve mollusks, but principally feeds on the Green-
land cockle (Serripes groenlandicus: Lowry and Frost,
Chapter 49, this volume).
Sea stars are used as food by red king crab in
shallow waters around Kodiak Island (Feder and
Jewett 1981) and perhaps also by this crab in the
Bering Sea. The distributions of two dominant
sea-star species and red king crab in the southeastern
Bering Sea (Figs. 69-10, 69-14, and 69-15) do not
overlap appreciably; the biomass of sea stars is
typically low where this crab is common. Sea stars
may actively avoid red king crab in areas with dense
populations of the crabs; an apparent avoidance
response of sea stars (Pycnopodia helianthoides) to
this crab in Kodiak waters is reported by Feder and
Jewett (1981). Sea stars and red king crab feed on
hard-shell clams whenever these are present; if
Paralithodes ate sea stars they would be reducing
competition for clam resources. A similar distribu-
tional relationship between snow crabs and sea stars is
not apparent. Snow crabs (Chionoecetes spp.) appar-
ently do not feed on sea stars; thus, asteroids and
snow crabs coexist in the Bering Sea (Figs. 69-9,
69-14, and 69-15). Sea stars and snow crabs do not
generally compete for food; Chionoecetes spp. feed
on a variety of small invertebrates rarely used by sea
stars.
The role of gametes as a source of carbon has been
1250 Benthic biology
180°
175'
170°
165°
160'
155°
170
Figure 69-11. Quantitative distribution of the total epifauna in the southeastern Bering Sea, 1975-76.
virtually overlooked in marine food webs. And yet
it is generally accepted that this material is of consid-
erably higher quality as food than somatic materieil
(see Isaacs 1976). The role of reproductive material
in marine trophic systems must be particularly
important when the gametes are derived from organ-
isms of low nutritional quality, i.e., species ordinarily
considered terminal members of food chains as adults
(e.g., sponges, coelenterates, echinoderms, and
tunicates). Thus, pulses of high-energy reproductive
material released during spawning of large popula-
tions represent important components of secondary
production in the Bering Sea as well as other marine
systems (see Feder and Jewett 1980 and Feder
et al. 1980a for distribution data of Bering Sea mac-
rofauna). Many larger invertebrates, as well as fishes,
produce vast quantities of gametes that are avail-
able as food to forms at lower trophic levels. Sperm
can be utilized by filter-feeding polychaetous anne-
lids, bivalve moUusks, and larvaceans. Eggs may be
taken by species that filter large particles, e.g., cope-
pods, euphausiids, salps, and larval and small fishes
and by adult clupeoids. The importance of repro-
ductive products as food is not restricted to sperm
and eggs, but also extends to the use of pelagic larvae.
Unlike terrestrial food webs in which reproductive
material constitutes an upward flux, reproductive
material in msirine food webs often exhibits a down-
Feeding interactions with emphasis on the benthos 1251
175
170'
165'
160"
Figure 69-12. Quantitative distribution of the clam Nucula tenuis in the southeastern Bering Sea, 1975-76.
ward flux, in which the carbon of higher forms moves
toward lower trophic components of the system. In
effect, forms such as sponges, copepods, and bivalve
moUusks may eat the gametes and larvae of a variety
of large invertebrates and fishes (Isaacs 1976).
As discussed in this chapter (see also appropriate
chapters in Section I, Volume 1 and Sections VII
and X of this volume), biological processes of the
southeastern Bering Sea are enhanced by a series of
three oceanic fronts acting in conjunction with
seasonal ice cover. These fronts play a major role
in the control of biological processes leading to
spatial separation of a pelagic food web within the
outer-shelf zone and a benthic food web within the
middle-shelf zone. Biomass and density of large
zooplankters, squid, and fishes, and densities of birds
and fin whales are highest offshore in the outer-shelf
zone (Iverson et al. 1979; Bakkala and Smith 1978;
C. Bublitz, unpub. data). In contrast, the benthic
food web, supporting the greatest densities and
biomass of benthic organisms in the southeastern
Bering Sea, is concentrated in the middle-shelf zone.
Further understanding of frontal systems on the
shelf of the southeastern Bering Sea, as well as of
their potential role in the northeastern Bering Sea,
is essential to comprehend food dynamics of this
very productive sea.
1252 Benthic biology
180'
175'
170°
165°
160°
155°
175
170°
165°
160°
Figure 69-13. Quantitative distribution of the cockle Clinocardium ciliatum in the southeastern Bering Sea, 1975-76.
Many studies have been conducted on predator-
prey interactions in marine ecosystems, but such
studies have seldom been directly used to interpret
the effect of human harvest of ocean products.
Management of meirine fisheries is typically predi-
cated on the use of such tools as recruitment, growth,
stock assessment, and catch-per-unit-effort. The
resolution and improvement of these management
tools may, in part, be brought about as we increase
our understanding of the dynamics of c£irbon flow
in the Bering Sea.
Humans, the top consumers in the Bering Sea food
web, play a significant role in the welfare of many
species. The overexploitation and decline of pink
shrimp, yellowfin sole, Pacific ocean perch. Pacific
herring, and Pacific halibut have been documented
(Pruter 1973, 1976). The recent trend of decline
in the average size of walleye pollock is also directly
attributable to fishing pressures (Pereyra et al. 1976).
Stocks of at least four species of marine mammals
(Pacific walrus, ribbon seal, fur seal, and sea otter)
have been significantly reduced in the past by over-
harvesting (Fay 1957, Chapman 1961, Shustov 1967,
Schneider, Chapter 51, this volume). It is expected
that competition between humans and marine
mammals for resources of commercial importance
will continue to intensify. The Marine Mammal
Protection Act and the Fishery Conservation and
Management Act were passed in an effort to achieve a
balanced management plan for marine mammals and
fisheries resources.
Feeding interactions with emphasis on the benthos 1253
Figure 69-14. Quantitative distribution of the sea star As^er/as amurensis in the southeastern Bering Sea, 1975-76.
The Bering Sea shelf is a multipurpose "commons"
(Hardin 1968) shared by humans and large resident
populations of marine organisms. Intelligent manage-
ment of this commons is essential if the Bering Sea,
one of the most productive marine systems in the
world, is to remain productive. Data presented in
this book and work currently in progress should
enable fisheries scientists to make predictions con-
cerning the future of the Bering Sea at its current
level of exploitation.
ACKNOWLEDGMENTS
This study, Contribution No. 433, Institute of
Marine Science, University of Alaska, Fairbanks, was
supported under contract #03-5-022-56 between
Howard M. Feder, the University of Alaska, and
NOAA, Department of Commerce, through the Outer
Continental Shelf Environmental Assessment Program,
to which funds were provided by the Bureau of Land
Management, Department of the Interior.
Distribution-bio mass maps were made possible
through the efforts of the data-processing staff of
the Institute of Marine Science, University of Alaska,
and particularly through the expertise of Cydney
Hansen and Frank Sommer. Drafting was accom-
plished by Ana Lea Vincent, Institute of Marine
Science. Work on shipboard and in the laboratory
by Institute of Marine Science, University of Alaska,
personnel contributed to collection and analysis of
much of the data presented here; we specifically
acknowledge Karl Haflinger, Max Hoberg, Bill
Kopplin, Kris McCumby, and Judy McDonald.
1254 Benthic biology
180°
175'
170°
165°
160°
155°
175'
170
165°
160°
Figure 69-15. Quantitative distribution of tiie sea star Leptasterias polaris acervata in the soutlieastern Bering Sea, 1975-76.
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asteroids. Oceanogr. Mar. Biol.
Ann. Rev. 18:57-124.
Smith, R. L., A. Paulson, and J. Rose
1978 Food and feeding relationships in the
benthic and demersal fishes of the
Gulf of Alaska and Bering Sea. In:
Environmental assessment of the
Alaskan continental shelf. NOAA/
OCSEAP, Final Rep. 1: 33-107.
Stoker, S. W.
1977
Report on a subtidal commercial
clam fishery proposed for the Bering
Sea. Rep. MMC-77/01. Mar. Mammal
Comm., Washington.
1978 Benthic invertebrate macrofauna of
the eastern continental shelf of
the Bering and Chukchi seas. Ph.D.
Dissertation, Univ. of Alaska, Fair-
banks.
Suyehiro, Y.
1942
Takeuchi, I.
1959
A study on the digestive system and
feeding habits of fish. Japanese J.
Zool. 10:1-303.
Food of king crab (Paralithodes
camtschatica) off the west coast of
Kamchatka in 1958. Bull. Hokkaido
Reg. Fish. Res. Lab. 20:67-75.
1967 Food of king crab Paralithodes
camtschatica off the west coast of
the Kamchatka Peninsula, 1958-1964.
Bull. Hokkaido Reg. Fish. Res. Lab.
28:32-44.
Tarverdieva, M. I.
1976 Feeding of the Kamchatka king crab,
Paralithodes camtschatica and Tanner
crabs, Chionoecetes bairdi and Chio-
noecetes opilio in the southeastern
part of the Bering Sea. Biologiya
Morya 2:41-8. (Transl. from Russian.)
Feeding interactions with emphasis on the benthos 1261
i
Tenore, K. R.
1977 Food chain pathways in detrital
feeding benthic communities. In:
Ecology of marine benthos, B. C.
CouU, ed., 37-53. Univ. of S. Carol-
ina Press, Columbia.
Trask, P. D.
1939 Organic content of recent marine
sediments. In: Recent marine sedi-
ments, Amer. Assoc. Petrol. Geol.
428-53.
Wilimovsky, N. J.
1974 Fishes of the Bering Sea: The state
of existing knowledge and require-
ments for future effective effort.
In: Oceanography of the Bering Sea,
D. W. Hood and E. J. Kelley, eds.,
243-56. Inst. Mar. Sci., Occ. Pub.
No. 2, Univ. of Alaska, Fairbanks.
Wilke, F.
1954 Seals of northern Hokkaido.
Mammal. 35:218-24.
J.
Tsalkina, A. V.
1969 Characteristics of epifauna of the
West Kamchatka shelf (from Problems
of commercial hydro bio logy). Fish.
Res. Bd. Can. Transl. Ser. No. 1568.
Walsh, J. J., T. E. Whitledge, F. W. Barvenik, C. D.
Wirich, and S. O. Howe
1978 Wind events and food chain dynamics
within the New York Bight. Limnol.
Oceanogr. 23:659-83.
1957 Food of sea otters and harbor seals
at Amchitka Island. J. Wildl. Man.
21:241-2.
Yasuda, T.
1967 Feeding habits of the zuwaigani,
Chionoecetes opilio elongatus, in
Wakasa Bay, 1: Specific composition
of the stomach contents. Bull.
Japanese Soc. Sci. Fish. 33:315-19.
(Fish. Res. Bd. Can., Transl. Ser. No.
1111.)
Sec
19
IH
Interaction of Sedimentary
and Water-column Re^mes
Interplay of Physical and Biological
Sedimentary Structures
of the Bering Continental Shelf
Hans Nelson,' Robert W. Rowland,^ Sam W. Stoker,^
and Bradley R. Larsen'
' U.S. Geological Survey
Menlo Park, California
^ U.S. Geological Survey
Reston, Virginia
^ University of Alaska
Fairbanks
ABSTRACT
Distinctive Holocene transgressive sand and post-
transgressive mud with attendant physical and biological struc-
tures occur on the shallow (<60 m) shelf of the northern Be-
ring Sea. Thin gravel lag layers, formed during the Holocene
shoreline transgression, veneer exposed glacial moraines. Epi-
faunal species dominate these relict gravel areas and cause
little disruption of physical structures. Some relict submerged
beach ridges contain faint rippling that probably is caused by
modern current reworking. Well-sorted medium sand on
exposed shoal crests is reworked by the sand dollar and
tellinid clam communities. Buried thin layers of transgressive
beach sand and gravel retain rare original medium-scale cross-
lamination and flat lamination that have been intensively
bioturbated. A thin layer of an offshore fine-grained sand
facies that was deposited by the Holocene transgression
remains unburied by modern mud in central Chirikov Basin.
Primarily because of ampeliscid amphipod bioturbation, this
facies has no physical structures.
Post-transgressive silty mud from the Yukon River blankets
the shallow (<20 m) areas of Norton Sound. In places the
silty mud contains thin beds of shells and pebbles and thin
sand interbeds and lenses that exhibit ripples and small-scale
flat and cross-lamination. These coarse-grained interbeds are
interpreted to be storm layers formed by modern storm waves
and storm-surge currents. Physical sedimentary structures
are well preserved only near the delta fringe; there the fre-
quency of physical reworking is highest, the potential for
preservation by a high rate of deposition is greatest, and the
inhibition of bioturbation by low salinity is most severe. At
greater distances from shore, infaunal deposit-feeding bivalves,
polychaete worms, and small amphipods cause progressively
greater disruption of bedforms in prodelta mud. Almost all
modern physical structures have been destroyed at water
depths greater than 25 m. As a result the following sequence
of storm deposits is characteristic of profiles extending away
from the delta: thick (>5 cm) storm-sand layers, thin storm-
sand layers, isolated and bioturbated sand lenses, faint bio-
turbated shell and pebble beds.
INTRODUCTION
The northern Bering Sea from St. Lawrence
Island to Bering Strait (Fig. 70-1) has continually
strong bottom currents, an extremely rich benthic
fauna, and a wide variety of sediment substrates.
These conditions, coupled with shallow continental
shelf waters that are affected by wave and tidal
current activity, produce a wide variety of physical
and biological sedimentary structures. Our purpose
is to map the distribution of these structures and to
correlate the distribution patterns with the control-
ling physical and biological factors. Such analyses
provide a model of factors controlling development
of physical and biological structures on continentEil
shelves in general and assist in specific paleoenviron-
mental reconstruction of ancient continental shelf
deposits.
Oceanographic setting
Three water masses have been defined on the
northern Bering shelf: Alaskan coastal water, Bering
shelf water, and Anadyr water (Fig. 70-2) (Coachman
et al. 1976). Alaskan coastal water, generated pri-
marily from the Yukon and Kuskokwim rivers and
other runoff (Fig. 70-2) (Saur et al. 1954), has pro-
nounced seasonal salinity changes. This is particu-
larly true in southern Norton Sound, where great
changes in discharge from the Yukon River occur
from summer to winter. Before June, salinities are
1265
1266 Interaction of sedimentary and water-column regimes
Figure 70-1. Setting, physiography, and location of large-scale bedforms presently known in the northern Bering Sea.
Bathymetry modified from Hopkins et al. (1976). Large-scale bedforms from Jordan (1962), Grim and McManus (1970),
L. Toimil (personal communication), and Nelson (unpublished data).
close to 30°/oo throughout southern Norton Sound.
During the summer and early fall salinities below
20^/00 are common (Fig. 70-2) (Goodman et al.
1942, Sharma et al. 1974).
Figure 70-2. Water masses in northern Bering Sea
(modified from Coachman et al. 1976). The Alaskan
coastal water (14-31. S^/oo, 0.8 C) occupies the eastern
portion of the study area, the Bering shelf water (some-
times called modified shelf water) (31.5-33*^/oo, 0-4 C)
covers the central area, and the Anadyr water (33°/oo,
1-3 C) occurs in the western portion of the study area.
Data on seasonal salinity changes from Goodman et al.
(1942), G. D. Sharma (personal communication), and
Nelson et al. (1975). Data on shorefast ice margin from
Thoretal. (1977).
Physical and biological sedimentary structures 1267
Typically, current speeds in the offshore part
(>30 km from shore) of the Alaskan coastal water
are 10 cm/sec near the bottom and 20 cm/sec near
the surface, and currents trend northward except
for the counterclockwise gyre into Norton Sound
(Fig. 70-3). Nearshore surface and bottom water
EXPLANATION
— *- water circulation
„I T maximu
bottom
° velocitie
m
current
es
cm sec.
/O — ^ depth in meters
100 km
68°
66 =
64"=
62 =
J I
- 60°
170
166'
158'
Figure 70-3. Offshore water circulation (from Goodman et al. 1942), and maximum bottom current velocities from
available measurements in northern Bering Sea (from Fleming and Heggarty 1966, Husby and Hufford 1971, McManus and
Smyth 1970, Nelson and Hopkins 1972).
1268 Interaction of sedimentary and water-column regimes
travels generally northward parallel to the Alaskan
coast at typical speeds of 30-40 cm/sec (Coachman
and Aagaard 1966, Fleming and Heggarty 1966,
Husby 1969, Husby and Hufford 1971, McManus
and Smyth 1970, Coachman et al. 1976).
The maximum current speeds are found where the
Alaskan coast protrudes westward and constricts
water flow. At the narrowest constriction, Bering
Strait, bottom speeds reach 180 cm/sec in water
depths of 55 m (Fleming and Heggarty 1966). Cur-
rents in the other two water masses are generally
slower, reaching a maximum of 50 cm/sec in eastern
Anadyr Strait amd minimums of 5-15 cm/sec in
central Chirikov Basin (Fleming and Heggarty 1966,
Husby and Hufford 1971, McManus et al. 1977).
Changes in atmospheric pressure and wind velocity
during storms can cause the current speed to fluc-
tuate by as much as 100 percent over periods of a
day or more (Coachman and Tripp 1970) and can
produce storm surges causing sea-level set-up of 4 m
along the southern coast of Seward Peninsula
(Fathauer 1975).
Calculations based on linear wave theory suggest
that the waves hindcasted for normal wind conditions
can affect the bottom to water depths of 20 m
(McManus et al. 1977). Wave reworking of bottom
sediments may extend considerably deeper during
intense storms. For example, the storm of November
1974 generated waves 6-7 m high and produced
water motion which might have been capable of
affecting the bottom at depths exceeding any found
in the northern Bering Sea (A. Sallenger, personal
communication).
Geologic setting
The entire northern Bering Sea floor is less than
60 m deep and generally flat, but it has distinctive
topographic features in several places (Fig. 70-1,
Hopkins et al. 1976). The eastern margins of both
Bering and Anadyr straits have relatively steep
scarps. Southeast of Bering Strait and in central
Shpanberg Strait, a series of linear ridges and de-
pressions is found. Large linear shoals also occur
off the northwestern and northeastern flanks of St.
Lawrence Island. The shallowest area in northern
Bering Sea is off the modern Yukon subdelta in
southern Norton Sound.
The northern Bering continental shelf is a mosaic
of modern and relict surface sediments. The relict
sediments formed in shallow water, at the strand,
or in subaerial environments at times when sea level
was lower than it is now (Fig. 70-4). During those
times continental glaciers pushed debris toward the
center of Chirikov Basin, and valley glaciers deposited
sediment several kilometers beyond the present
shoreline of Seward Peninsula (Nelson and Hopkins
1972). Shoreline regressions and transgressions,
most recently during the rise of sea level since 18,000
B.P., reworked the glacial moraines, leaving a lag
gravel on the sea floor north and west of St.
Lawrence Island and along the southern side of
Seward Peninsula. Transgression of the shoreline
across the Bering shelf blanketed the remainder of the
Chirikov Basin with a relatively coarse grained basal
layer ranging from medium-grained sand to gravel
with an overlying thin layer of fine sand. Except in
central Chirikov Basin, the transgressive deposits are
only a few tens of centimeters thick and overlie
Pleistocene glacial debris, alluvium, and freshwater
mud and peat dated at 10,500 b.p. or older (Nelson
and Hopkins 1972, Nelson and Creager 1977).
Holocene sandy silt mainly originating from the
Yukon River (hence sometimes called Yukon mud)
has been deposited in Norton Sound. This sediment
forms deposits tens of centimeters thick in parts of
central Norton Sound and several meters thick off
the present subdelta and around the margins of
Norton Sound (Nelson and Creager 1977). Currents
apparently have inhibited deposition of Holocene
Yukon sand and silt over the older relict transgres-
sive sand and gravel found in Chirikov Basin
(McManus et al. 1974).
Biological setting
The continental shelf of the northern Bering Sea
is an area of rich macrobenthic standing stock
(Neiman 1961, Filatova and Barsanova 1964,
Kuznetsov 1964, Rowland 1972, Stoker 1973),
albeit of relatively low diversity in major species
(Stoker 1973). Major faunal communities are in-
completely defined, but affinities of species for sedi-
ment types have been defined for shelled forms
(Rowland 1973), and association patterns for other
taxa have been delineated for some regions of the
southeastern Bering Sea (Stoker 1978). The primary
benthic ecosystem is based mainly on a detrital food
web (Kuznetsov 1964), although there are other
feeding types, such as the sessile seston feeders of
the Bering Strait.
A major problem in describing either trophic
structure or distribution of the Bering Sea benthos
is the extreme patchiness of the populations. Such
patchiness is incompletely understood, but it results
from a combination of variable habitats and biolog-
ical interactions (Stoker 1973 and unpub.).
The dominant organisms of the infaunal macro-
fauna are polychaete worms, bivalve moUusks, am-
peliscid amphipods, and ophiuroid and echinoid
Physical and biological sedimentary structures 1269
I70°W
158°
ALASKA
64°N
\
\
64°N
SEDIMENT TYPE
Modern
=1^ Yukon silt (>507o)
0 50 100
I 1 1
Kilometers
l^-^^ Yukon very fine sand (>50%)
Palimpsest - Relict sand with-
20-50% modern silt
Relict
vvj 20-50% modern very fine sand
I .'■.'■.'■. 'I Holocene tronsgressive fine sand (>80%)
f'.';*/'.^ Glaciol or bedrock-denved grovel (>50%)
Figure 70-4. Surface sediment distribution in northern Bering Sea (modified from Nelson and Hopkins 1972; Knebel and
Creager 1973, McManus et al. 1974, 1977).
echinoderms; other forms, such as sipunculids,
gastropods, holothurians, and tunicates, may be
locally dominant (Neiman 1961, Rowland 1973,
Stoker 1973 and unpub.). Inferences about the
bioturbating capabilities and substrate preference
of some taxa can be drawn from general accounts
of functional morphology (Stanley 1970), distribu-
tional studies in other areas (Ockelmann 1958), and
Alaskan studies (Table 70-1).
Methods of study
One hundred twenty box cores were taken from
the northern Bering Sea shelf at water depths greater
than 10 m (Fig 70-5). The cores were sectioned
to 1-cm slabs, photographed, and x-rayed; the tex-
ture, stratigraphy, and structures were then des-
cribed (Fig. 70-5). Identification of fauna was based
primarily on specimens from the >2-mm sediment
fraction of 25-kg van Veen grab samples (Nelson
and Hopkins 1972, Rowland 1973, Stoker 1973).
Photographs of live fauna observed in box cores at
the time of collection were also available. These data
were compiled to estimate distribution and abun-
dance of types of structures and benthic fauna in the
region.
PHYSICAL SEDIMENTARY STRUCTURES
External form
Pebble lag layers consist predominantly of clasts
4-64 mm in diameter (Fig. 70-6a and b) with little
matrix, although large boulders in lag areas off
TABLE 70-1
List of most common bioturbating organisms; where known, their substrate associations
and type of sediment disturbance is given.
Depth
Substrate and
group
Organism^
distribution
Living habits
Data source
Surface
Brachyuran crabs
Create shallow
Stoker unpub.
disturbers
Chionoecetes opilio
Chionoecetes hairdi
Ubiquitous
Ubiquitous
surface depressions
Fig. 70-10
Hyas coarctatus
Ubiquitous
Same as above
Telmessus cheiragonus
Anomuran crabs
Pagurus spp.
Ubiquitous
Paralithodes sp.
Seasonal and uncertain
Crangonid shrimps
Crangon spp.
Ubiquitous
Ophiuroid echinoderms
Ophiura sarsi
Ophiura maculata
Stegophiura nodosa
Gorgonocephalus caryi
Echinoid echinoderms
(6%) Strongylocentrotus
droebachiensis
Muddy silt, nearshore Create extensive
surface tracks
Silty sand
Create shallow
surface depression
Fig. 70-12;
Neiman 1961
Fig. 70-10
Stoker unpub.
Fig. 70-10
Gravel and pebble lags
Shallow
bioturbaters
Gastropod mollusks
(19%) Tachyrhynchus
erosus
(15%) Natica spp.
(9%) Neptunea spp.
(7%) Polinices spp.
(2%) Buccinum spp.
Bivalve mollusks
(36%) Yoldia myalis
(16%) Yoldia hyperborea
or amygdalea
Ubiquitous, most
common nearshore
Ubiquitous
Ubiquitous
Ubiquitous
Surface trails and
shallow burrows when
preying
Predatory, drilling bivalves
Scavenger and predator
creating trails and shallow
burrows
Predatory, drilling bivalves
Scavenger
Most common in muddy Deposit feeders
sediment, but wide-
spread in all environ-
ments
Mud or muddy sand Deposit feeder?
Fig. 70-10
Rowland 1973
Schafer 1972
Fig. 70-10,70-11
Rowland 1973
Stanley 1970
Fig. 70-11 and 14
Stanley 1970
Rowland 1973
(15%) Nucula tenuis
Nuculana radiata
Clinocardium
cilia turn
Mud or muddy sand
Mud or muddy sand
Sandy silt substrates
Deposit feeder?
Deposit feeder?
Suspension
feeders
Figs. 70-11,70-12
Stanley 1970
Rowland 1973
Petrov 1966
Tellina alternidentata
Current-winnowed
clean sand
Figs. 70-13 and 14
^Within some groups the species are listed in order of abundance and where known the percentage of occurrence at sampling
stations is given in parentheses in front of the species.
1270
Table 70-1, Cont.
Depth
group
Organism
Substrate and
distribution
Living habits
Data source
Amphipoda
Protomedeia sp.
Melita sp.
(27%) Hippomedon sp.
Haploops laeuis
Pontoporeia femorata
Mud and fine sand
Mud and fine sand
Mud and fine sand
Mud and fine sand
Mud and fine sand
Detritus feeders, one
or more of these
species create U-shaped
and vertical burrows
with widened circular
area
Polychaeta
(8%) Nephthys
Haploscoloplos
elongata
Sternaspis scutata
Pectinaria hyperborea
Brada sp.
Ubiquitous
Fine,silty sand
nearshore
Errant polychaete
Burrows parallel
to bottom surface
Fig. 70-13
Fig. 70-10
Echinoidea
(11%) Echinarachnius
parma
Sorted-medium sand
on shoals
Shallow horizontal
burrows
Fig. 70-10
Lisitsyn 1966
Intermediate
bioturbaters
Bivalve mollusks
(58%) Serripes
groenlandicus
(45%) Macoma calcarea
Venericardia
crebricostata
Liocyma fluctuosa
Echiuroidea
Ubiquitous
Ubiquitous, sandy
silt and sand
Sandy silt
Sand and sandy silt
Filter feeder
Detritus and
filter feeder
Detritus and
filter feeder
Detritus and
filter feeder
Fig. 70-10
Coan 1971
Echiurus echiurus
Fine to coarse sand
Deposit feeder
Amphipoda
(28%) Ampelisca sp.
Byblis gaimardi
Silty sand
Detritus feeder
that builds narrow,
V-shaped, mucus-
lined tube
Figs. 70-11 and 14
Polychaeta
Myriochele herri
Onuphis sp.
Spiophanes bombyx
Ubiquitous
Fine sand
Figs. 70-10 and 11
Deep
bioturbaters
Holothuroidea
(1%) Cucumaria
calcigifera
Detritus feeder
Fig. 70-10
Tunicata
(3%) Polonia corrugata
Sand to gravel
1271
Filter feeder
Fig. 70-10
1272 Interaction of sedimentary and water-column regimes
Table 70-1, Cont.
Depth
Substrate and
group
Organism
distribution
Living habits
Data source
Bivalve mollusks
(28%) Mya truncata
Ubiquitous, hard
sand or mud
Filter feeder
Figs. 70-10 and 11
Quayle 1970
(1%) Myapriapus
Filter feeder
(7%) Spisula polynyma
Sand
Deep burrowers
Chamberlain and
alaskana
and filter feeders
Steams 1963
(1%) Sipunculida
Golfingia margaritaceum
Polychaeta
All deposit feeders
(9%) Lumbrinereis
Ubiquitous
Errant Polychaeta (?)
Fig. 70-10
(4%) Amphareta
Tube-builder
Fig. 70-10
Maldane sarsi
Mud and silt
Tube-builder
Praxillella praetermissa
Axiothella catenata
Nome have been reported by divers (G. E. Greene,
personal communication). Generally, the pebble
lags occur at the sediment-water interface in layers
5-15 cm thick (Fig. 70-6a). However, a well-sorted
"pea gravel" interpreted to be on an ancient beach
strandline at a depth of 30 m in Anadyr Strait is more
than 32 cm thick (Fig. 70-6b). These surficial pebble
lags generally overlie glacial till but locally cover
bedrock outcrops in topographically elevated regions
(Nelson and Hopkins 1972) (Figs. 70-1, 70-4, 70-5,
and 70-7).
Shell lag layers in the subsurface, several centi-
meters thick and composed entirely of shell debris,
were encountered in transgressive sands at several
locations off north central St. Lawrence Island
(Fig. 70-6). They were also found in well-sorted,
medium-grained sands on shoal crests of Shpanberg
Strait and southeast Bering Strait (Fig. 70-6d). Clam
shells predominate in layers off St. Lawrence Island,
while fragments of sand dollars make up layers of
the shoal crests. In the region southeast of Bering
Strait, basal coarse-grained, pebbly sands commonly
have a high content of shell fragments, but not
enough to be classified as shell layers.
Lag layers of mixed pebbles and shells are wide-
spread in the upper subsurface, particularly in the
mud of the shallow northern and eastern parts of
Norton Sound (Figs. 70-5 and 70-6g). However, a
few such layers occur in subsurface basal coarse sand
and gravel at water depths of 40 m or greater in the
strait areas (Figs. 70-4, 70-5, 70-6h, and 70-7). In
both of these situations, shell and pebble concentra-
tions range from distinct layers a few centimeters
thick, composed entirely of pebbles and shells (Fig.
70-6c), to diffuse zones 5-10 cm thick containing
a matrix of sand and silt (Fig. 70-6h).
Solitary rafted pebbles are ubiquitous in all water
depths, bathymetric settings, and sediment types
(Figs. 70-4 and 70-7). They are most common in
sediment surrounding gravel deposits (Fig. 70-4),
although solitary cobbles up to 20 cm in diameter
were encountered in Yukon mud far from gravel
sources (Fig. 70-6j).
Storm-sand layers are most common in silty muds
of the shallow parts of southern Norton Sound
(Figs. 70-4, 70-5, 70-6e, f, and g), but a few thin
(<1 cm) coarse- and medium-grained storm-sand
layers are found in fine sand on deeper scarps
(>40 m) southeast of Bering Strait (Figs. 70-4, 70-5,
70-6i, and 70-7). The sand layers in Norton Sound
are typically 1-2 cm thick except close to shore,
where they are thicker (Figs. 70-6e-g). In the shal-
lowest sampling sites near the main distributaries of
the present Yukon subdelta, surface sand layers 4-12
cm thick have been detected in areas where mud was
sampled in previous years.
In addition to the changes in distribution at the
surface, the abundance of sand layers varies with
depth in the subsurface. For example, off Stuart
Island approximately 20 sand layers occur in the
uppermost 12 cm of the core, and none are found in
the next 12 cm of the core (Fig. 70-6f). In a long
(132 cm) core of Yukon sediment from southeastern
Norton Sound, four sand layers were found from
0 to 15 cm, two from 15 to 60 cm, and two from
60 to 132 cm.
Physical and biological sedimentary structures 1273
PHYSICAL STRUCTURES
Figure 70-5. Box-core locations and descriptions of physical sedimentary structures observed in the upper 40 cm of
sediment in the northern Bering Sea. Structures in relict transgressive deposits and figure numbers of text photos are keyed
to location.
Internal structures
Flat lamination is the most common and widely
distributed internal structure in all sediment types,
water depths, and topographic settings (Figs. 70-5
and 70-7). It is observed most often in sand layers
of Norton Sound, where the lamination is about 1
mm thick and is defined by minor variations in grain
size (Fig. 70-6f and g). Lamination is least common
in gravels, where layers are about 1 cm thick (Fig.
70-6b). The best examples of flat lamination are
found in pre-Holocene deposits of limnetic mud
(Fig. 70-8a). Although the whiteness of some lami-
nae suggests volcanic ash or diatom varves, no glass
shards or microfossils were found under the micro-
scope.
Cross lamination, like flat lamination, is widely
distributed and is best developed in the sand layers
of Norton Sound. Characteristically the sets of
cross-laminae are of small scale and are inclined at
low angles (Figs. 70-4, 70-6f and g). Crossbedding in
gravel is rare, but when observed is larger in scale and
higher in dip angle than in finer-grained sediment
(Figs. 70-6b and 70-8a).
Ripples are very common at the tops of sand layers
of Norton Sound and in sand at the margin of
Chirikov Basin (Figs. 70-5 and 70-7). The ripples
are generally asymmetric and small in scale (6-8 cm
wavelength, 1.5-5 cm wave height) and are inter-
preted to be current ripples and combined flow rip-
ples commonly found in sand or silt (Harms et al.
1274
o
ton c
CD
C5
^ O
ttJDrt
c o
■C o
oa
.S «o
3
C S
O T!
J= O
O .
a D,
O) _c
3 fc;
CUD o
fa -s
C a>
CU)
c
a;
a;
Physical and biological sedimentary structures 1275
Figure 70-6a. Transgressive lag gravel over glacial till
shown in box-core slab face. Note Hemithiris psittacea
(brachiopod) and bryozoan skeletons on surface. Water
depth 41 m.
Figure 70-6b. Epoxy cast of box core containing thick,
well-sorted transgressive lag gravel from —30 m shoreline
stillstand (Nelson and Hopkins 1972). Note faint cross-
bedding in center of cast. Water depth 30 m.
Figure 70-6c. Box core-slab face exhibiting shell lag at
base of transgressive fine-grained sand. The shell layer
was composed of equal amounts of Hyatella arctica and
Macoma calcarea and probably formed as a storm lag
during lower sea level. The layer was found in an isolated
small basin at a water depth of 43 m.
Figure 70-6d. Bioturbated coarse sand and shell layer
composed entirely of Echinarachnius parma (sand dollars)
in current-winnowed fine sand over a shoal crest. Water
depth 35 m.
Figure 70-6e. Box-core slab face showing thick light-
colored storm-sand layers in Yukon silt 30 km from the
modern Yukon subdelta. Note that the thick upper sand
most recently formed is not bioturbated, whereas only
cross-laminated sand lenses remain in the lower bioturbated
bed. Water depth 11m.
Figure 70-6f. Radiograph of well-defined thin storm-
sand layers in late Holocene Yukon silt 75 km offshore
from the present subdelta. Thoroughly bioturbated older
Yukon silt underlies well-structured beds in younger
Yukon silt (after Nelson and Creager 1977). Note rippled
and wavy bedded sand beds (light-colored) with small-
scale cross and flat lamination. Water depth 16 m.
Figure 70-6g. Radiograph showing shell and pebble
lags in the upper and lower parts of the core and numerous
thin sand layers in between. Both probably developed by
storm reworking of Yukon silt 110 km from the present
Yukon subdelta. Note that upper shell lag is only slightly
disrupted, whereas basal layers are highly bioturbated.
The middle unbioturbated section has sand beds (light-
colored) that exhibit discontinuous parallel bedding in the
upper two layers and nonparallel and lenticular bedding
in the lower three layers. Wood at the core base had an
age of 2,120 years b.p. (Teledyne Isotopes sample No.
1-7320). Note the burrows 1 mm in diameter in the upper
part of the core, probably caused by polychaete worms (see
Howard 1969, Figs. 8, 13 and Hertweck 1972, Figs. 3, 5).
Water depth 14 m.
Figure 70-6h. Radiograph showing bioturbated shell
and pebble lag layers (lower half of core) in transgressive
coarse to medium sand. Lag apparently developed during
the Holocene transgression. Overlying fine-grained trans-
gressive sand in the upper half of the core is highly bio-
turbated by amphipods and clams. Water depth 47 m.
Figure 70-6i. Box-core slab face of medium-grained
sand from a shoal crest containing coarse sand lag layers
and clay laminae probably formed by current reworking.
Water depth 31 m.
Figure 70-6J. Yukon silt containing a large rafted peb-
ble. Note thin sand lenses near the surface. Water depth
18 m.
WATER
DEPTH SEDIMENT BOTTOM
(meters) TYPE RELIEF
PHYSICAL STRUCTURE
Pebble lag
Shell lag
Shell & pebble lag
Solitary rafted pebbles
Storm sand layers
Flat lamination
Cross lamination
Ripples
Ice gouge
Structures in gravels
All samples
Figure 70-7. Frequency of various physical sedimen-
tary structures in different depth, substrate, and topo-
graphic settings.
HI
W{
roH
pm^^ ^'
. r ^
. V
V
.s
a.
s
a>
00
o
3
OB
1276
Physical and biological sedimentary structures 1277
Figure 70-8a. Radiograph showing the following se-
quence: transgressive fine-grained sand overlying trans-
gressive pebbly medium-grained sand with flat lamination
and medium-scale cross-lamination, which overlies pre-
transgressive limnetic clays with freshwater ostracods
(P. Valintin, personal communication). Note deep burrow-
ing probably by Mya sp., after marine transgression (see
Fig. 29, Mya arenaria burrows, in Reineck 1970). Water
depth 36 m.
Figure 70-8b. Plan section of a ripple set impression at
a parting surface near the bottom of a box core, together
with an epoxy slab cross section (adjacent upper right)
showing the same dark-colored lower sand layer and
another surface sand layer. Note that apparent ripple
crests (dotted line) are irregular and asymmetric with
tongue-like projections (cf. Harms et al. 1975, Fig. 3-7
and Reineck and Singh 1973, Fig. 30). Ripple index
(length /height) is 5-8 basal and 10-12 for surface sand
layers. Water depth 12 m.
Figure 70-8c. Radiograph of remnant asymmetric
ripples that have been altered by bioturbation of medium-
grained shoal crest sand. Water depth 21.9 m.
Figure 70-8d. Core slab face showing loading, slump
or ice-disrupted structures (near the core bottom) in
laminated late Pleistocene mud deposited before the
Holocene transgression. Mud contains freshwater ostra-
cods (see reference for Fig. 70-8a). These have an age of
14,920 years b.p. (Teledyne Isotopes No. 1-7318), based on
organic carbon from a whole sediment sample. Water
depth 51 m.
Figure 70-8e. Radiograph showing highly contorted
sand lags possibly caused by ice push or scour of the sea
floor. Note shallow U-shaped burrows caused by small
amphipods and large, deep burrow (on the right) probably
made by a clam. Water depth 12 m.
1975) (Figs. 70-6f and g). Where sand layers are
thick, ripple forms appear to be nearly continuous
(Figs. 70-6f and g), unless bioturbated, in which
case the ripples are disrupted, producing sand lenses
(Fig. 70-6e).
Miscellaneous structures
Natural load and slump structures are observed in
laminated Pleistocene lake deposits in a large depres-
sion off St. Lawrence Island (Fig. 70-8f). Other load-
like features are present near the tops of some box
cores, but they are suspected to be coring artifacts
(Fig. 70-6f). Extremely disturbed sediment in a
box core from the shallow area near the Yukon sub-
delta is the only apparent example of structures
related to ice gouging (Fig. 70-8e). It seems paradoxi-
cal that ice gouging, as new studies show, is ubiqui-
tous at depths less than 20 m over the northern
Bering Sea floor (Thor et al. 1977) and yet rarely
produces noticeable effects in box cores (Fig. 70-9).
Large-scale bedforms such as sand waves have a wide
distribution where topography and bathymetry con-
strict bottom currents (Figs. 70-1, 70-3, and 70-9)
(Jordan 1962, Grim and McManus 1970). Charac-
terization of these large bedforms and ice-gouge
effects must await detailed investigation with side-
scan sonar.
BIOTURBATION
Once the primary physical structures associated
with erosion and deposition have developed, secon-
dary processes such as slumping, loading, and bio-
turbation begin. In this generally flat continental
shelf region, biogenic structures usually predominate
over other secondary structures in the upper 30 cm
of the sediment.
The size of the area and the patchiness of the
benthos (Stoker 1973) make it impossible to map
benthic faunal distribution in detail or to correlate
all types of structures with the organisms. Where
single or very limited types of bioturbation charac-
terize certain broad areas of the sea floor, complete
biologic structures can be traced to certain species.
In other areas some species— sand dollars, for exam-
ple, are restricted to certain habitats (Table 70-1,
Figs. 70-6i, 70-8c, 70-9, and 70-10), and although the
fact that they disturb shallow sands can be docu-
mented (Fig. 70-1 3a), no distinct structures can be
identified. Commonly only parts of burrows are
observed in box cores, and the burrow may not be
assignable to a single species (Figs. 70-13 and 70-14);
this is particularly true for the numerous species of
burrowing clams. Fortunately, distribution of each
major group of bioturbating organisms (surface,
shallow, intermediate, and deep) can be outlined
by analysis of screened macrofauna from grab
samples (Rowland 1973, Stoker 1973) (Figs. 70-10
and 70-11).
Surface disturbers
Several species of small organisms disturb the
sediment surface over large areas of the Bering Sea
floor (Fig. 70-10 and 70-12). Brittle stars are one of
the dominant organisms in the eastern Bering Sea
(Neiman 1961), but they are most common in muddy
areas closer to land and least common in the central
Chirikov Basin (in Fig. 70-10 note the absence of
brittle stars at the predominant sandy 30-40 m depth
offshore in the Chirikov Basin). Distinctive surface
tracks of brittle stars can be identified on the top
surfaces of box cores, but burrows (Hertweck 1972)
are not evident even where massive populations cover
the bottom (Fig. 70-12).
1278
Physical and biological sedimentary structures 1279
Figure 70-9a. Sand dollar pavement covering current-
winnowed shoal crest at 36 m.
Figure 70-9b. Oscillation ripples on sand ridge crest at
9 m during severe storm.
Figure 70-9c. Asymmetric ripples on shoal crest, as
in Fig. 70-9b, with strong unidirectional currents during
non-storm conditions in water depth of 17 m.
Figure 70-9d. Sonograph showing large-scale sand waves
over crests of sand ridges at a water depth of 30 m.
Figure 70-9e. Sonograph showing intense ice scour
that covers most of sea floor in 10-20 m of water (water
depth 14 m). There are no sidescan data in less than 10 m
of water.
The carnivorous gastropods also occasionally leave
surface trails but may burrow to shallow depths
after prey; they are widespread, except in the shallow
region around the Yukon subdelta (see Tachyrhynchus
in Fig. 70-10), where they occur rarely. Crabs and
sea urchins typically are found on gravel substrates,
and both may excavate slight depressions; however,
they are fewer in number than the other surface-
disturbers (Fig. 70-10). Crabs are common also in
sandy areas except for the central Chirikov Basin.
In response to the benthic food resources, large
populations of walrus, bearded seal, and gray whale
inhabit the northern Bering Sea at least seasonally
and are likely to be responsible for considerable
reworking of the shallow sediments over much of
the northern Bering shelf. Gray whales are known to
disturb bottom sediment to a depth of several centi-
meters to feed mainly on amphipods (Tomilin 1975).
The distribution of the large amphipod populations
(Fig. 70-11) and the pathways of whale migration
(Nasu 1974) suggest that gray whales may cause
surface disturbance in the Chirikov Basin area.
Walrus and bearded seals also may disturb the sedi-
ment surface as they feed upon large bivalves and
other infauna (Fay and Stoker unpub. data).
Shallow burro wers
The most widespread shallow burrowers (0-5 cm
depth) are small, bright-colored amphipods possibly
of the genera Protomedeia, Melita, and Hippo-
medon (Fig. 70-11). These taxa are most abundant
off southeastern St. Lawrence Island and in the
western and northern areas of Norton Sound, where
they inhabit patches of Yukon-derived sediment.
One or more of these species probably is the builder
of U-shaped burrows about 5 mm in diameter (Figs.
70-13c and d). Completely preserved burrows are
WATER
DEPTH
(meters)
SEDIMENT
TYPE
BOTTOM
RELIEF
BIOTURBATING
ORGANISM
Strongylocentrotus
(urchins)
Tachyrhynchus
erosus
(gastropod)
Ophiuroids
(brittle stars)
Crabs
Ech inarachnius
parma
(sand dollar)
Yoldia myalis
(clam)
Small
amphipods
Pectinaria
Nephthys
Ampeliscid
amphipods
Serripes
groenlandicus
(clam)
Small polychaete
(ca. 1 mm)
burrows
Maldanjdae
My a truncata
(clam)
Ampharete
Lumbrinereis
ALL
SAMPLES
ir> o ino lo o
— C\J OJ lO lO 'J-Q
_ (0 — (C — U) ,
CJ<NJ ro ro A
E-,-
= .E § « 8
c/> •»- M b u
° 3 »
Figure 70-10. Frequency of various surface, shallow
(0-5 cm), intermediate (0-10 cm) and deep (0-: 10 cm)
bioturbating species versus water depth, substrate, and
topographic setting.
1280 Interaction of sedimentary and water-column regimes
SHALLOW STRUCTURES (0-5cm)
II 1 1 1|| Small amphipod tubes, common-abundant
r -] Shallow clam burrows, rare-common
ryyy] Lumbrinereis burrows, rare-common
INTERMEDIATE STRUCTURES (0-10cm)
Ampeliscid amphipod tubes, common-
abundant
Small polychaete burrows, common-
abundant
DEEP STRUCTURES (0->10cm)
[mill Deep clam burrows, rare-common
I I Unidentified deep burrows, common-a^ndant
^^^ Ampharete burrows, rare-common
^
0 50
Kilomoters
Figure 70-11. Distribution of the most common shallow
(0-5 cm) (a), intermediate (0-10 cm) (b), and deep 0->10
cm) (c) biological structures that could be identified. Note
that small amphipod tubes in a, ampeliscid tubes in b,and
unidentified deep burrows in c are present everywhere in
at least some quantity.
distinctive, but fragments are not distinguishable
from burrows made by polychaete worms such as
Nephthys (Fig. 70-13d). In general, we believe most
incomplete burrows were constructed by the more
abundant amphipods (Figs. 70-10 and 70-11).
Several species of shallow-burrowing gastropods
(Table 70-1) with no positively identified burrowing
structures are present throughout northern Bering
Sea except off the Yukon Delta (Figs. 70-10 and
70-13). Tubes of the polychaete Pectinaria are also
widespread (Fig. 70-10) (Stoker 1973). The latter
organisms are known to develop shallow burrows
(Hertweck 1972), but no identification can be made
in Bering Sea sediment. Numerous bivalves, such as
Yoldia, Macoma, Nuculana, Tellina, and Nucula
(Rowland 1973, Stoker 1973) are undoubtedly
responsible for widespread shallow disturbance, but
have not produced distinctive burrows.
Intermediate burrowers
Intense bioturbation from the sediment surface to
a depth of 10 cm can be discerned in central Chirikov
Basin 8ind southwest and southeast of St. Lawrence
Island. In these areas, abundant populations of large
tube-building ampeliscid amphipods live in fine-
grained sand (Figs. 70-14a and b. Table 70-1). In
most other areas, except central and southern Norton
Sound, burrows 1 mm in diameter made by small
polychaete worms are common to abundant. These
structures are particularly common in the silty mud
on the northern and eastern margins of Norton Sound
(Figs. 70-11, 70-6g, 70-15C and d). Bivalves such as
Serripes and Clinocardium are particularly abundant
throughout the northern Bering sea region; however,
amphipod burrowing in Chirikov Basin and poly-
chaete burrowing in Norton Sound appear to oblit-
erate most other physical and biological structures
at intermediate depths.
Deep burrowers
Bivalves such as Mya and Spisula are the most
common deep-burrowing (0->10 cm) organisms.
Their widespread distribution suggests that many
deep burrows are caused by pelecypods (Figs. 70-11
and 70-15, Table 70-1). Only rarely (Fig. 70-8a)
is it possible to correlate the burrow type with clam
species, since normally only portions of the burrows
are evident.
Several species of polychaete worms, sipunculids,
and holothurians also burrow deep into the sedi-
ments. Though deep-burrowing worm species occur
throughout the area, they are most common in silty
and very fine grained sand in deeper water (Figs.
70-10, 70-11, and 70-15a and b).
DISCUSSION
Factors controlling distribution of physical
sedimentary structures
Relict structures in relict sediments
The physiced sedimentary structures of the north-
em Bering Sea are either relict from Quaternary
conditions or developed by modern wave and bottom
currents. In places, the Holocene shoreline trans-
gression reworked Pleistocene moraines and bedrock
outcrops exposed on the sea floor. The fine-grained
Physical and biological sedimentary structures 1281
Figure 70-12a. Surface-disturbing organisms and sea-
floor traces in nortiiern Bering Sea. Piiotograph of
box-core surface showing surface trails of brittle
star Ophiura sarsi on Yukon silt. Water depth 14 m.
debris was winnowed out, leaving behind surface lag
gravel deposits (Fig. 70-6a) (Nelson and Hopkins
1972). These deposits remain on the surface of
current-winnowed topographic elevations where dep-
osition of Holocene muds has been prevented. In the
eastern parts of Anadyr and Bering straits as well as
along nearshore southwestern Seward Peninsula and
St. Lawrence Island, the mineralogy and large grain
size of gravel lags, together with early radiocarbon
dates (15-40,000 b.p.: Nelson, unpub. data) of
underlying sediment, indicate deposition under
older, high-energy conditions not present today
(Nelson and Hopkins 1972, McManus et al. 1974).
The coarser grain size and different mineralogy of
the Chirikov Basin sand blanket compared to the
silty-sized sediment of the main modern Yukon
sediment source suggest that Chirikov Basin sand
also is relict.
Relict physical structures in relict sediments are
best preserved in the subsurface sediment of strait
areas with the deepest water, where present-day wave
effects are minimal, coarse gravel armors the bottom
surface, and strong currents prevent burial by modem
deposits. Here, box cores have penetrated into older
transgressive sediments and even into Pleistocene
freshwater deposits with relict lamination (Fig.
70-8d). Coarse-grained relict sediment overlying
Pleistocene tills contains flat lamination and asso-
ciated high -angle, medium-scale cross bedding that
evidently originated during the Holocene shoreline
transgression (Figs. 70-6a and b, 70-4, and 70-7).
Subsurface shell and pebble horizons in such relict
Figure 70-12b. Serripes groenlandicus that has severe-
ly disturbed the box-core surface of Yukon silt. Water
depth 18 m.
sediments are now in sufficiently deep water and
buried deep enough to ensure isolation from modern-
day storm-wave and bottom -current effects. These
structures apparently formed as storm lags during
lower sea-level stands (Figs. 70-6c and 70-6h).
w^m
¥^
rj^^
•^'
*>
i
f
^,
N
y - /
^
Figure 70-13. Shallow-burrowing (0-5 cm) organisms and their structures in the northern Bering Sea.
1282
Physical and biological sedimentary structures 1283
Figure 70-13a. Ampharete sp. burrows shown in radio-
graph of core 207. Sediment type is clayey silt. Water
depth 42 m.
Figure 70-13b. Field photograph of Ampharete sp.
tubes and worms from box-core 207 surface just after
collection.
Figure 70-1 3c. Photograph of box -core vertical and
horizontal surface showing cemented tubes and subsur-
face mucus-lined burrows of sabellid-terribellid worms that
occur in large numbers within muddy gravels. Note also
the live shallow-burrowing Yoldia sp. in the upper center
of photograph. Water depth 27 m.
Figure 70-13d. Photograph of box-core vertical slab
face showing burrow of tunicate Pelonia corrugata in fine-
grained transgressive sand. Note characteristic corrugations
of burrow. Water depth 44 m.
Figure 70-13e. Field box-core photograph showing Holo-
thurian Cucumaria calcigera burrowing vertically down-
ward through very fine sand. Water depth 37 m.
Figure 70-13f. Photograph of box-core vertical slab
surface showing burrowing of polychaete worm (probably
Lumbrinereis) in fine-grained sand. Water depth 19.6 m.
Figure 70-13g. Box-core photograph of horizontal bur-
row of Macoma brota from specimen living at the time
of core collection. Sediment is Yukon silt and burrow is
at a depth of 7 cm from the sediment-water interface.
Water depth 19 m.
Modem structures in relict sediments
The relict fine-grained sand of central Chirikov
Basin is interpreted to have been deposited as a
nearshore belt of sand that migrated along with the
Holocene shoreline as it transgressed across the
continental shelf. Since the modern Yukon silt
has not prograded over the transgressive sand, it has
been exposed to intense bioturbation for thousands
of years. Moreover, because the Chirikov Basin sand
has been covered by 35-55 m of water since the sea
reached its present level several thousand years ago,
the development of physical sedimentary structures
by waves has been limited. Bottom currents in this
central area are generally sluggish (Fig. 70-3)
(McManus et al. 1977) and in most places are prob-
ably insufficient to develop structures. Even though
waves or bottom currents occasionally possess suffi-
cient energy to create structures in this noncohesive
sediment, the binding effect of the dense network of
ampeliscid amphipod tubes probably inhibits forma-
tion of such structures (Fig. 70-14b) (Rhoads 1970).
Consequently, the sand is completely devoid of
sedimentary structures except on a few shoal crests
where the sediments are reworked by strong bottom
currents (Figs. 70-6i and 70-8c).
Recent evidence from sidescan sonar, underwater
television, and vibracores verifies physical formation
of sedimentary structures in certain shoal areas of
relict sediment in Chirikov Basin. In the shallower
upper parts of sand ridges with sand waves (Figs.
70-1, 70-4, and 70-9), the surface and near-surface
coarse-sand and shell storm lags (Fig. 70-6d), along
with faint ripple structures (Figs. 70-6i and 70-8c),
appear to be near-surface modifications of relict sand
by modern storm waves and bottom currents. On
underwater television, storm waves have been ob-
served to winnow shell pavement and to superimpose
small-scale oscillation ripples over the larger sand-
wave structures (Figs. 70-9a and b). Sidescan sonar
records show large-scale asymmetric sand waves
covering ridge tops and trending northward in phase
with the present strong northward bottom currents
in the northeastern Chirikov Basin (Fig. 70-3, Fig.
70-9c) (Nelson et al. 1977, Nelson 1977); a radio-
carbon dating of 1,000 b.p. (Teledyne Isotopes
1-9773) on wood from a depth of 30 cm in a sand-
wave field documents recent modification of sedi-
ments by sand-wave formation during the present
stand of high sea level.
Either wave or current effects could be responsible
for faint ripple structures observed in specific box
cores from sand ridges. However, the dominance
and type of asymmetric sand-wave and ripple fields
in all sidescan records and bottom photographs
from the region indicate that most modern ripple
structures in Chirikov Basin must derive from bottom
current activity (Fig. 70-9).
Modern structures in modem sediments
Numerous radiocarbon dates substantiate that the
blanket of mud with interbedded sand in Norton
Sound has a Holocene origin and contains contempor-
ary sedimentary structures (Nelson et al. 1975,
Nelson and Creager 1977). Development and preser-
vation of these physical structures varies widely
both spatially and stratigraphically over the con-
temporary surface in Norton Sound. A change from
complete bioturbation to complete preservation of
physical structures within the past several thousand
years can be demonstrated in several locations (Figs.
70-6f and g). In those locations closest to the Yukon
Delta, such dramatic alteration in preservation of
physical structures may be attributable to salinity
and circulation changes caused by a shift in location
of a major Yukon distributary (Fig. 70-6f, Nelson
and Creager 1977).
The storm-sand layers that are interbedded vdth
mud surrounding the Yukon Delta contain the best-
developed physical sedimentary structures because
1284 Interaction of sedimentary and water-column regimes
Figure 70-14a. Radiograph of large amphi-
pod (Ampelisca macrocephala) tube struc-
tures occurring in great abundance in fine
transgressive sand of central Chirikov Basin.
Box core 237 from water depth of 27 m.
Figure 70-14b. Field photograph of surface
of box core 237 taken immediately after
collection. Silt-like, mucus-lined burrows
shown are typical of large amphipod species
Ampelisca macrocephala.
Figure 70-14. Intermediate-burrowing (0-10 cm) organisms and their structures.
of several interacting factors. The prodelta area is
subject to intense and frequent wave reworking
because of its extreme shallowness. In addition, the
shape of Norton Sound acts to focus storm-surge
set-up of water level (Fathauer 1975), and this in
turn results in development of strong bottom currents
as storm-surge water runoff moves northward from
the region (Fleming and Heggarty 1966, Nelson and
Creager 1977). Such runoff currents are probably
the last mechanism of a storm-surge event to rework
and form physical structures in sand layers of the
prodelta area.
Formation of the thickest sand layers and their
rapid burial due to the high sedimentation rates in
the prodelta both inhibit bioturbation and enhance
preservation of the physical structures. Even more
important, the low salinity and more extensive ice
formation in the prodelta (Figs. 70-2 and 70-11)
appear to restrict faunal populations and consequent
bioturbation of the physical structures. The com-
plete bioturbation of physical structures at similar
water depths but in normal salinity on the northern
side of Norton Sound appears to confirm this
hypothesis.
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1286 Interaction of sedimentary and water-column regimes
Much of the cross-lamination and lenticularity in
modem sand layers of Norton Sound appears to
result from rippling by unidirectional bottom cur-
rents. The ripples are usually asymmetric, and the
ripple form, where it can be observed in box cores,
bottom photographs, underwater TV, and sidescan
sonar, is sinuous and irregular, not straight-crested
like oscillation ripples (Nelson 1977; Figs. 70-8 and
70-9). Furthermore, the basal surfaces on sand layers
are regular, the internal structure conforms to ripple
form, and bundle wise buildup or offshoots passing
from adjoining troughs and crests are absent. Each
of these points suggests formation primarily by
unidirectional bottom currents (Reineck and Singh
1973).
Waves are important in forming bottom struc-
tures, and formation of oscillation ripples over asym-
metric ripples and sand waves has been observed in
Chirikov Basin at water depths similar to those of
Norton Sound (Nelson et al. 1977) (Fig. 70-9).
Hindcasting of wave data indicates that wave re-
working c£in affect most of the Norton Sound sea
floor (McManus et al. 1977). However, in the areas
of very fine sand and at water depths of >10 m,
Clifton's (1976) conceptual model predicts that
wave-related currents will not produce asymmetric
rippling. Apparently, the dominant storm effect on
sand layers is reworking by bottom currents, which
are intensified by storm-induced sea-level changes
(Fathauer 1975). Later modification by less intense
wave effects may cause some oscillation ripples to be
superimposed over the dominant unidirectional
features, but in general they appear to be subordinate.
Eastward and northward from the present delta,
storm-sand layers become fewer and fewer, and only
diffuse storm layers rich in shells and pebbles are
observed. Near the delta, where biota appears to be
restricted and no rocky headlands are present, few
shells or pebbles are encountered in storm layers.
With increasing distance from the delta into water
of higher salinity, more and more shells are encount-
ered and bioturbation increases. Furthermore, the
intensity of storm-wave reworking decreases and
sand layers become thinner; headlands along the
coast away from the delta provide a source of pebbles.
Figs. 70-6e to g, 70-6j, 70-1 3b to d exemphfy such a
proximal (delta) to distal (central Norton Sound)
or shallow- to-deep sequence of storm layers. The
change from sand layers to coarse lags of pebbles
and shells offshore also suggests that processes change
from mainly transport and deposition of sand sheets
to mainly erosion of mud, leaving pebble and shell
lags offshore.
The Yukon muds of Norton Sound, some massive
and some interbedded with storm sand layers, remain
nearly devoid of physical structures, except for
occasional laminations (Fig. 70-1 3b and e). Because
the mud deposition is slow and continual under non-
storm conditions, bioturbation apparently can almost
always keep pace with the formation of physical
structures; hence physical structures are not generally
preserved in muds.
Present-day pebble rafting and ice gouging
Isolated pebbles, widespread in sediment of the
Bering Sea region, may have been transported by
several processes. Pebbles are most common in
areas surrounding seafloor gravel (Fig. 70-4). This
distribution pattern may result from ice grounding in
gravel areas. The ice may pluck pebbles from the
gravel source and drop them nearby after the iceberg
works free and begins melting. Other mechanisms
such as transport of walrus gastroliths (stomach
stones) (S. W. Stoker and F. H. Fay unpub. data)
and sea-grass rafting (Stoker 1973) may also carry
isolated pebbles offshore.
Recent studies indicate that gouging into the sea
floor by icebergs occurs everywhere at depths shal-
lower than 20 m (Thor et al. 1977) (Fig. 70-9); and
in strait areas ice jams may cause gouging at much
greater water depths (G. Bloom, personal communica-
tion). The gouging is most intense (reaching depths
of up to 1 m in the sediment) in the prodelta area
surrounding the modern Yukon subdelta; this is the
same region where physical sedimentary structures
are best preserved (Fig. 70-5). The question remains,
why does this intense gouging have so little effect on
physical structures? Perhaps sediment rates are rapid
enough near the modern subdelta to keep ahead of
the rate of ice gouging.
Factors controlling bioturbation
Biological factors
A few ubiquitous species the distribution of which
is little affected by environmental factors account for
a significant amount of the bioturbation everywhere
in the northern Bering Sea. Examples of these species
have been described in the previous bioturbation
section: the ophiuroid and gastropod (Tachyrhynchus
erosus) surface disturbers, the clams (e.g., Yoldia
myalis) and small amphipod shallow burrowers, the
clams (e.g., Serripes groenlandicus) and small poly-
chaete (thread worm) intermediate burrowers, and
clams (e.g., Mya truncata) and large polychaete (e.g.,
Ampharete) deep burrowers (Table 70-1, Figs. 70-10,
70-11, and 70-12).
Physical and biological sedimentary structures 1287
Except for the cosmopolitan species just men-
tioned, distribution of most species is controlled by
environmental factors such as hydrographic condi-
tions, morphologic setting, and substrate type. Con-
sequently, bioturbation by most species has definite
patterns of areal distribution (Figs. 70-10 and 70-11).
All species appear to be restricted by the seasonally
low salinity off the modern Yukon subdelta (Figs.
70-2, 70-5 and 70-11, Lisitsyn 1966). Regions of
strong currents and resulting coarse-grained sediment
support epifaunal communities such as the assem-
blages of suspension feeders found in straits, or the
sand dollar (Echinarachnius parma) and bivalve
communities (Tellina lutea alternidentata, Spisula
polynyma) found in sandy areas on crests of shoals
(Fig. 70-10).
Because of the narrow depth range (0-50 m) on
the northern Bering shelf, water depth has little
direct influence on the abundance or type of bio-
turbating organisms. Instead, benthic communities
typically show pronounced association with sub-
strate. For example, the large ampeliscid amphipods
are the dominant organisms disturbing the trans-
gressive fine-grained sand in Chirikov Basin (Figs.
70-10 and 70-11, Table 70-2). They are not evident
in Yukon silt of Norton Sound, where the smaller
amphipods, brittle stars, and deposit-feeding worms
and clams are predominant (Figs. 70-10 and 70-11;
Table 70-1) (Rowland 1972, 1973). Gravel lags are
habitat for an abundant epifauna of rocky substrate
type consisting of bryozoans, barnacles, and brachio-
pods. However, the thickness and coarseness of the
lag layers and the sessile living habits of the fauna
on them seem to prevent significant bioturbation.
Many other substrate associations of bioturbating
organisms, particularly bivalves, have been outlined
in other Bering Sea studies (Table 70-1) (Rowland
1972, 1973; Stoker 1973 and unpub.).
Interplay of biological and physical factors
Intensity of bioturbation is controlled by the rates
of several processes: the frequency of formation of
physical structures, the rate of reworking by organ-
isms, and the sedimentation rate (Fig. 70-16).
Changes in these rates through geologic time cause
variations in the intensity of bioturbation at a site.
The following physical factors cause an increase in
the rate of formation of physical sedimentary struc-
tures and a decrease in intensity of biogenic rework-
ing: shallow water with intense wave reworking,
swift bottom currents, rapid rates of deposition,
and low-salinity water. These physical variables and
other environmental characteristics like those men-
tioned in the previous section control species dis-
persal and cause patchiness of faunal distribution.
As a result, the rate of biogenic reworking varies from
one location to the next and with time at a given
location.
In the shallow prodelta region off the Yukon
River subdelta, bioturbation typically does not keep
pace with the formation and rapid burial of physical
structures (Fig. 70-5). An area just east of the pro-
delta near Stueirt Island also shows no bioturbation in
deposits of the last 5,000 years (Figs. 70-5 and 70-6J;
Nelson and Creager 1977). This is true even though
the area has low sedimentation rates and is at a
greater water depth, where the formation of wave-
formed structures is expected to be slower. The well-
developed physical structures probably result from
the shoreline constriction of coastal currents. The
extremely good preservation of physical structures
here and in the prodelta may result both from con-
tinued formation by bottom currents or waves and
from the inhibition of biogenic activity by the great
seasonal changes in salinity. Complete bioturbation
of sediment older than 5,000 years near Stuart
Island strongly suggests that Yukon Delta distribu-
taries shifted into the region after 5,000 b.p. (Nelson
and Creager 1977) and that salinity is the predomi-
nant factor controlling bioturbation in this area.
Another stratigraphic sequence for the last 2,000
years in eastern Norton Sound (Figs. 70-5 and 70-6g)
shows complete bioturbation in the lower third of the
sediment, nearly complete preservation in the middle,
and complete bioturbation in the upper third. Either
faunal populations diminished during the time of
deposition of the middle sequence, or frequent
storms prevented bioturbation from keeping pace
with deposition.
GEOLOGIC SIGNIFICANCE
Geologic effects of bioturbation
In addition to disturbing physical structures and
creating trace fossils, bioturbation may severely
disrupt fossil assemblages and organic debris used in
dating deposits. The disruption is especially severe
in regions of thin transgressive sequences such as the
continental shelf of the northern Bering Sea. In
several cores (Figs. 70-8a and d), present-day burrows
extend at least 30 cm into Pleistocene freshwater
deposits that are tens of thousands of years old.
This downward homogenization of Holocene sedi-
ment by bioturbation helps to explain radiocarbon
dates of only a few thousand years for older buried
transgressive deposits (Figs. 70-6i and 70-8d; Tele-
dyne Isotopes 1-7482, 7483). Likewise partly because
of this upward mixing of older materials, radiocarbon
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Physical and biological sedimentary structures 1289
HIGH ENERGY
(INNER) SHELF
LOW ENERGY
(OUTER) SHELF
UJ
t-
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Figure 70-16. Conceptual model showing importance of physical structures versus biological structures in shelf sediments.
Thickness of wedge depicts relative intensity of process from high-energy to low-energy shelf environments. Current and
wave fields could be of various sizes depending on current or wave domination of a given shelf. All areas of physical structures
would shift seaward with higher energy (see arrow) or toward shore with lower energy. Unidirectional current features on
shelves will be more common seaward of nearshore wave structures, but the frequency of structures will relate to current
intensity rather than distance seaward (for example, see Fig. 70-7).
dates of 1,740 to 5,085 b.p. are found for bulk
organic carbon in the top 1-2 cm of modem surface
sediment on the northern Bering shelf (Teledyne
Isotopes 1-8134, 8135, 8226, Fig. 70-6f).
Radiocarbon dating of calcium carbonate of shells
again suggests significant biologic mixing of modern
shells downward into buried transgressive gravel and
sand (Fig. 70-6b, c, h, and i). Fossil surface-dwelling
mollusk species are just several hundred years old,
even though only those shells buried in older sedi-
ment far below the organisms' normal living habitat
were dated (M. Rubin, USGS Radiocarbon Lab.
W-2462, 2464, 2466, 2467, 2681-2685). In Chirikov
Basin, where the transgressive sequences are thin and
dating of shells does not appear to be reliable, mixed
modem and transgressive foraminiferal assemblages
are found throughout the entire transgressive se-
quences (Figs. 70-8a and d; R. Echols, personal
communication). Only where high sedimentation
rates produce rapid, deep burial, as happens near the
modem Yukon subdelta, do radiocarbon dates of
shells and organic carbon agree with stratigraphy (M.
Rubin, USGS, Radiocarbon Lab. W-26180; Teledyne
Isotopes 1-7316, 8134); here unmixed transgressive
sequences of microfossils can be detected.
Rhoads (1970) points out another aspect of bio-
turbation that may have particular geologic signifi-
cance for the northeastern part of the Bering shelf.
The predominance of deposit feeders cam reduce the
bulk density of fine-grained sediment and greatly
enhance the potential for erosion. The dominance of
deposit feeders in Norton Sound (Figs. 70-10 and
70-11) (Rowland 1972) may contribute to the
resuspension of considerable fine-grained sediment
1290 Interaction of sedimentary and water-column regimes
there. The resuspension of sediment by storm waves
and its removal by storm-generated and continuous
currents may have displaced about half of the Holo-
cene sediment of Yukon source from Norton Sound
to the Chukchi Sea (Nelson and Creager 1977).
Comparison of Bering shelf and similar
sedimentary environments
Prodelta and inner-shelf facies
Prodelta mud facies develop in the shallow regions
surrounding the mouth of the Yukon River, where
the low-salinity river plume is the dominant water
mass (Figs. 70-2 and 70-5). The proximal deposits
are characterized by thin mud interbedded with
thick storm-sand layers that contain well-developed
sedimentary structures resulting from waves and
currents generated by storm surge (Table 70-2, C^ ).
Offshore from the most proximal prodelta facies,
layers become thinner, more highly rippled, well
structured with cross lamination, and increasingly
bioturbated. The most distal prodelta deposits are
dominated by highly bioturbated muds with sand
lenses containing bioturbated remnants of physical
structures. Farther seaward, storm-lag layers rich in
shells and pebbles occur (see Figs. 70-6e, f, and g,
7 0-1 3b, and 7 0-1 4c for a specific sequence; Figs.
70-5 and 70-16 show general patterns of distribution).
Bioturbation in the muddier facies is dominated by
tube-building detritus feeders and burrowing deposit
feeders (Table 70-1, C to G; Figs. 70-10 and 70-11;
Table 70-2, C^ ).
The physical and biological structures in similar
ancient stratigraphic sequences reflect this same
proximal-to-distal energy gradation. For example,
proximal-to-distal sequences of physical structures
and storm-sand layers like those in Norton Sound are
described for Jurassic deposits by Anderton (1976).
In the Upper Cretaceous Blackhawk formation in
Utah, a regressive sequence begins with completely
bioturbated offshore muds (Howard 1972). Sand
beds appear up-section and thicken upward with
increasingly well-preserved physical structures, indi-
cating greater wave energy. The fauna also changes
up-section from deposit to suspension feeders as the
depositional environments shallowed.
Variations in wave climate and topographic setting
can greatly extend or reduce proximal-to-distal
offshore gradation of physical structures generated
by waves. For example, in the Gulf of Gaeta in the
low-energy wave climate of the Mediterranean, well-
developed physical structures are limited to less than
6 m of water depth (Reineck and Singh 1973), below
which bioturbation predominates. In the higher-
energy environments of the northern Bering Sea and
off Southern California, well-preserved recent physi-
cal structures exist to water depths of 15-20 m
(Figs. 70-5 and 70-7) (Karl 1975). In the very high
energy environment off Oregon, well-preserved
physical structures occur in sediments in over 50 m
of water (Kulm et al. 1975). Well-preserved physical
structures may also exist anomalously far offshore on
topographic elevations.
Sediment type and rate of influx also may in-
fluence the maximum offshore extent and water
depth at which physical structures are preserved. In
muddy areas, such as near deltas, fine-grained sand
layers and their structures are readily identifiable in
modem or ancient sequences (Fig. 70-6e to g) (Moore
and Scruton 1957, Masters 1967, Howard 1972).
Commonly, in the most distal locations of deposi-
tion, isolated pods or lenses of rippled and laminated
sediment are the last recognizable vestige of a storm-
sand layer (Figs. 70-6J and 70-13b) (Reineck 1970,
Winston and Anderson 1970). Such thin sand lenses
are usually destroyed by bioturbation closer to shore
or at shallower depths than similar storm-lag layers
composed of shell and pebble lags (Figs. 70-5 and
70-7). For example, faint shell and pebble horizons
of coarse-grained storm lags are identifiable to a water
depth of 30 m in modern sediments of Norton
Sound even after very extensive bioturbation; the
last vestiges of fine-grained sand layers occur in 25 m
of water (Fig. 70-7). In most delta areas, the forma-
tion of such shell and pebble layers is inhibited by the
paucity of rocky headland pebble sources and by the
influx of fine-grained sediment and low-salinity
water, which appears to discourage large populations
of bivalve mollusks, the source of most shell material.
The distribution pattern of the prodelta facies may
be controlled as much by water circulation and fresh-
water plume dispersal as by the shallow, nearshore
location and shape of the prodelta topography
(Figs. 70-2, 70-3, and 70-5), because variations in
salinity and oxygen and nutrient content of sea
water can influence benthic productivity and thus
affect the formation and preservation of physical
structures. The best preservation of physical struc-
tures coincides with the location of the low-salinity
plumes (Figs. 70-3 and 70-5) (Nelson et al. 1975)
surrounding the Mississippi and Yukon deltas; a pro-
gressive reduction in bioturbation also has been
correlated with decreasing salinity up estuaries
(Winston and Anderson 1970, Moore and Scruton
1957). The importance of salinity compared to other
factors, hke rapid sedimentation, is suggested by thin
(12 cm) late Holocene sequences off the Yukon that
have remained unbioturbated for at least 5,000 years
(Fig. 70-6f).
Physical and biological sedimentary structures 1291
In some geographic settings physical structures
may be preserved unexpectedly in continental shelf
areas where the benthic fauna is depauperate because
of low oxygen content in bottom water (Seibold
et al. 1971). Excellent preservation of physical
structures found in the Mesaverde Formation of
northwestern Colorado (Masters 1967) suggests that
these ancient deposits similar to those off the Yukon
were formed under shallow, low-salinity water near
a delta, or where environmental factors inhibited
bioturbation.
Transgressive and current-winnowed facies
The transgressive fine-grained sands in the northern
Bering Sea are characterized by a homogeneous
texture, the general absence of physical structures,
and intense bioturbation by tube-building detritus
feeders (Table 70-2, B^ ). This sediment facies may
typify thin transgressive sands on continental shelves
with low wave energy, but where burial by offshore
mud is prevented by strong bottom currents or iso-
lation from sediment sources. In contrast, in areas
where there is a very high energy wave regime,
like the area off Oregon mentioned earlier, some
physical structures are found in the offshore relict
transgressive sand facies (Kulm et al. 1975).
The basal transgressive gravel and pebbly coarse-
to medium-grained sand of the Bering shelf in many
places overlie Pleistocene moraines either as surface
relict deposits or as subsurface strata beneath trans-
gressive fine sand. These coarse-grained transgressive
sediments take several forms that may be distinguish-
able in the stratigraphic record. The deposits with
rounded pebbles, water- worn and thick-shelled
mollusks, and medium-scale cross and flat lamination
appear to be typical sediments associated with shore-
line stillstands (Table 70-2, A2 ) (Clifton et al. 1971,
Reineck and Singh 1973). The angular pebble lags
that develop over glacial till and bedrock apparently
form during very rapid shoreline transgressions.
Distinguishing characteristics of such deposits are
angular gravels, little or no fine-grained matrix, and
the remains of a rocky intertidal fauna (Table 70-2,
Aj ). Sessile benthic fauna is largely epifaunal (Craig
and Jones 1966). As a result, the thin pebble lags
show little disruption from bioturbating organisms
and may remain well preserved in the stratigraphic
record. For example, thin, structureless, transgressive
sands overlying well-preserved glacial deposits have
been noted in the Paleozoic transgressive sequence of
the Algerian Sahara region (Beuf et al. 1971).
The well-sorted current-winnowed medium sand on
the shoal crests of the northern Bering shelf is
another sediment facies that may be recognizable in
ancient shelf deposits (Table 70-2). Remnants of
ripples and flat lamination are common; shell-lag
horizons and clay stringers, possibly representing
major fluctuations in currents, are locally present.
An important key to such deposits in ancient se-
quences would be dominance of sand dollars and
filter-feeding bivalves or similar ancient organisms
(Table 70-2, B2 ).
Shelf model
The physical and biological structures observed
on the Bering shelf agree with other similar studies;
these data permit conceptualization of a model of
typical shelf sedimentary structures and factors
controlling their distribution on an open shelf with
clastic deposition dominated by muds and no organic
reefs (Fig. 70-16). The inshore margin of the model
presented here phases into the well-defined shore-
line sequences of physical structures caused by break-
ing waves that have been depicted in the conceptual
models outlined by Clifton et al. (1971). The model
presented here does not consider the series of large-
scale bedforms caused by extremely strong bottom
currents in constricted bathymetric regions with
high tidal or dynamic current flux. Such sequences
have been described by Belderson et al. (1971) in
the English Channel shelf and appear to be present
also in the Bering Strait area (Figs. 70-1, 70-4, and
70-16).
In the model we present, physical sedimentary
structures caused by waves v^dll dominate the open-
shelf sediment just offshore from beach-related
features. The best-developed physical sedimentary
structures caused by strong bottom currents asso-
ciated with periodic tides (Mofjeld 1976), storm
tides, and shoreline constrictions of dynamic currents
will generally occur just offshore from the wave-
related structures. Seaward from strong wave- and
tide-formed sedimentary structures, there occurs a
spatial series of physical structures resulting from
waning wave and bottom-current processes asso-
ciated with storms. This complete sequence of
storm-sand to pebble- and shell-rich layers has been
well documented in Norton Sound (Fig. 70-16).
As physical energy from waves and currents
diminishes offshore, the frequency of physical
sedimentary structures lessens, and the physicEil
structures are bioturbated and replaced by trace
fossils to a progressively greater degree. The sequence
of biological structures indirectly follows gradients
of wave and current energy, because these gradients
regulate substrate types, the main control on bio-
logical assemblages (Craig and Jones 1966, Rowland
1973, Stoker 1973). Typically, suspension-feeding
1292 Interaction of sedimentary and water-column regimes
organisms will be more prominent nearshore in
coEirse-grained substrates associated with high physi-
cal energy. In this environment, filtering apparatus
is less likely to be clogged by fine-grained debris
(Rhoads and Young 1970), and the circulation of
suspended debris is vigorous. Suspension-feeding
organisms will tend to disturb sediment less because
they need only to anchor on or into the bottom
surface, not to burrow through the sediment, to
acquire food. In contrast, discrete burrows and
complete bioturbation characterize offshore muds
(Howard and Frey 1973), because deposit feeders and
detritus feeders require the higher content of organic
debris found in fine-grained sediments of lower-
energy settings.
The conceptual model (Fig. 70-16) portrays an
open graded shelf that gradually changes in depth,
wave energy, sediment character, and current energy
offshore. Evidence from the northern Bering conti-
nental shelf and elsewhere indicates that many vari-
ables, including topographic setting, hydrographic
characteristics, biologic productivity, and type and
location of sediment sources can modify this ideal-
ized sequence. Several examples have already been
cited to show that variation of wave climate can
greatly extend or reduce the offshore extent of
physical structures created by waves.
Topographic projections outwaird from the adjac-
ent shorelines, such as deltas, or upward from the
surrounding sea floor, such as offshore sand ridges
(Nelson et al. 1975), are important variables con-
trolling the development of current-formed physical
structures. Where water circulation is constricted
and strengthened by major shoreline projections, as
in the Bering Strait or English Channel (Belderson
et al. 1971), bedforms and internal physical struc-
tures will be weU developed no matter what the water
depth or distance from shore. Offshore areas of sea-
floor topographic relief, such as sand ridges, that
constrict and focus bottom currents are also sites
of well-developed physical structures no matter how
far they are from shore (Fig. 70-61).
Variation in the amount and type of sediment
also influences the development and preservation of
physical structures. Where rates of deposition are
high and interbedded muds are common, as they are
off the Yukon and Mississippi deltas (Moore and
Scruton 1957), preservation of physical structures is
enhanced and may extend to unusually great depths
or distances from shore, considering the wave-energy
setting. The final shell and pebble remnants of an
offshore storm layer may extend offshore far beyond
the distance usually expected if unusual sources of
pebbles exist or mechanisms like ice or organic raft-
ing disperse them over the shelf.
The effect of increased wave energy, current
velocity, and deposition rates, in addition to de-
creased benthic productivity, is to extend areas
dominated by physical sedimentary structures farther
seaward than bioturbation would otherwise allow
(Fig. 70-16). These variations in basic physical,
chemical, and biological conditions are predictable at
least partially and must be considered when sedi-
mentary structures are used for paleoenvironmental
reconstructions.
ACKNOWLEDGMENTS
Discussions with Asbury H. Sallenger, Jr. and H.
Edward Clifton helped in interpreting physical
structures, and George Mueller similarly helped with
identifications of benthic fauna. Microfaunal analysis
by Ronald Echols and Page Valintine and radiocarbon
dating by Meyer Rubin assisted stratigraphic interpre-
tation. Excellent x-ray radiography was provided by
David Pierce. Compilation of data and preparation of
figures was ably completed by Dennis Kerr and Lee
Bailey. For assistance with sample collection we
thank scientists and crews of the following research
ships: OSS Oceanographer (NOAA), OSS Surveyor,
OSS Rainier (NOAA), and R/V Thomas G. Thompson
(University of Washington). Beneficial review com-
ments were provided by Ralph E. Hunter and Asbury
H. Sallenger, Jr.
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Section
Summary and Perspectives
(
L
Consideration of Environmental Risks
and Research Opportunities
on the Eastern Bering Sea Shelf
Donald W. Hood
Friday Harbor, Washington
John A. Calder
NOAA Office of Marine Pollution Assessment
Rockville, Maryland
ABSTRACT
Remarkable progress has been made in understanding the
eastern Bering Sea shelf in the last eight years. The reasons
why it is so highly productive and why it supports such large
numbers of commercial species, birds, and mammals are now
becoming clear. From this understanding, environmental
risks from noise, physical disturbance, platform discharges,
and oil spills are tentatively evaluated, and the conclusion is
drawn that, with awareness, proper planning, and common
sense, the risks can be made acceptable. Unacceptable risks
are those which could cause permanent loss of important
populations or retard the recovery of an adversely affected
ecosystem. The evaluation of risk from oil spills has made
it clear that there are unmet information needs critical for
adequate risk analysis and proper planning. Both government
and industry have a responsibility for providing the resources
to meet these needs as well as for actions to mitigate impacts
and assess the damage resulting from accidents if they do
occur. Applied science is possible only when a firm base of
fundamental knowledge exists. The eastern Bering Sea shelf
is as well studied as any continental shelf in the world. This
strong knowledge base provides a unique opportunity for
interdisciplinary studies which can integrate living resources,
physical processes, climate, and human activity and perhaps
achieve the ultimate goal of predictive modeling.
INTRODUCTION
In 1976, when one of us^ wrote the introduction
to the book Assessment of the Arctic Marine En-
vironment (Hood and Burrell, editors, 1976), con-
cern was expressed that in our quest for fossil fuels
to supply a politically uncertsiin, energy-dependent
world we might discard the basic requirement of
Donald W. Hood
estimating the impact on a renewable resource
(particularly one of the magnitude found on the
Bering Sea shelf) before undertaking activities re-
quired for extraction and development. Five years
have passed since then, and it is encouraging to reveal
that extensive and impressive scientific efforts have
been made to understand the Bering Sea shelf. A
good beginning is evidenced by the results presented
in the two volumes of this book. This remarkable
progress in only a few years has led many to believe
that understanding this system to the point of the
ultimate goal— predictability— may be within reach.
We know that we are dealing with a finely tuned
ecosystem most of the energy of which goes into
unexploited resources such as marine mammals,
birds, invertebrates, and noncommercial fishes. We
believe that we now know enough to be able to
assess the major risks and perhaps estimate damage
that might result from accidents of sizable propor-
tions. There are, however, uncertainties about the
effects on this finely tuned ecosystem of chronic
disturbances, whether they be from contaminants,
noise, or other human influences, and of increased
exploitation of the living resources. Politics, more
extensive ecosystem analysis, and predictive modeling
will determine how these uncertainties are resolved.
It would be foolhardy indeed to reduce the force
of scientific investigation of the Bering Sea shelf at
this time simply because we have gained some scien-
tific knowledge that can be used to react to the
1299
1300 Summary and perspectives
public outcry that would result from a major acci-
dent from oil and gas development. These incidents
historically have required or used relatively little
scientific knowledge, but rather require engineering
cleanup technology, communications, and time for
recovery. The greater problems confronting science
in the future are related to development of tech-
niques for rational damage assessment— finding out
the long-range effects of disturbances on any biolog-
ical resource of interest and how much of a resource
can be lost without preventing recovery, how signif-
icEint contaminants get into the ecosystem and what
becomes of them— along with the continuing pursuit
of a basic understanding of the system that must
accompany the application of science to any problem
concerning human activity.
This two -volume presentation considers only basic
science, which these editors believed to be more
easily documented without having to consider applied
problems simultaneously. Now that this task has
been accomplished, we are ready to use this and any
other documentation available to consider the risks to
this environment associated with oil and gas develop-
ment. Our treatment here is not extensive, but will
serve as an introduction to concepts and ideas impor-
tant to those who will follow this work with various
syntheses, impact statements, and plans for future
research projects.
LEASE SCHEDULE AND RESOURCE
ESTIMATES
The Bureau of Land Management identifies six
outer continental shelf planning units in the Bering
Sea: Bering-Norton Sound, Northern Bering Shelf,
Bristol Basin, North Aleutian Shelf, St. George Basin,
and Navarin Basin (Fig. 71-1). No sales are currently
scheduled in Northern Bering or Bristol Basin. There
are four Bering Sea sales on the June 1980 OCS
leasing schedule. At this writing, three of the lease
areas have been through the tract selection stage
(Fig. 71-2). A summary of the major milestones
and the resource potential for each sale is given in
Table 71-1. In May 1981, a revised lease sched-
ule which includes ten sales in the Bering Sea before
1987 was proposed by the U.S. Department of the
Interior.
EVALUATION OF ENVIRONMENTAL RISKS
There are four major sources of environmental
risks from oil and gas development: noise, physical
disturbance, normal operational discharges, and
accidental spills.
Figure 71-1. OCS planning units in the Bering Sea.
Noise
Noise can come from several sources, including
platform operations, aircraft, and workboat traffic.
Noise can disrupt normal activities at bird colonies
and mammal rookeries, and result in reduced repro-
ductive success. There is concern that vessel traffic
and platform noise could disrupt the migratory be-
havior of whales. The adverse effect of noise can be
eliminated by establishing buffer volumes at each
major bird colony and mammal rookery and requiring
strict observance of the buffer volumes. Defensible
evidence of adverse effects of noise on whale migra-
tion will be difficult to obtain. Yet even this poten-
tial impact could be reduced by suspending noise-
causing operations in the migratory path during the
most critical weeks of the migratory season. With
proper advance planning it may be possible to effect
such a suspension at little cost.
Physical disturbance
Physical disturbance results from emplacing plat-
forms, laying pipelines, or constructing coastzd
facilities. Such activities are site-specific and affect
limited zones. However, impacts can range from
severe to trivial, depending on the exact location
selected for an activity. Here again, advance planning
is the key to reducing environmental risk. Those who
are responsible for siting decisions must become
familiar with the living and cultural resources of the
area and include protection of these resources in
their planning processes from the beginning.
Figure 71-2. Tracts selected for sale.
The environmental risks from both noise and
physical disturbance can be minimized, if not elim-
inated, by thoughtful planning and strict observance
of sensible operating procedures. Environmental
sensitivity, caution, and common sense are the main
requirements for overcoming these environmental
risks. The risks from normal operational discharges
and accidental spills are more complex.
Platform discharges
Of the discharges to the environment resulting
from oil and gas development, the discharge of mud
and cuttings appears to be of most concern and will
be the only one discussed in this chapter.
Drilling fluids or "muds" perform a number of
functions during the drilling process: they remove
cuttings from the bore hole, cool and lubricate the
TABLE
Environmental risks and research opportunities 1301
drillstring and bit, form a filter cake on the wellbore
which helps prevent losses in permeable formations,
control high-pressure fluids in rock formations,
suspend cuttings and heavy materials when circula-
tion is interrupted, support part of the weight of the
drillstring, control formation damage, facilitate well-
logging, and transmit hydraulic power to the drill bit
(McGlothlin and Krause 1980). All of these func-
tions are essential to the completion of a well. The
chemical additives commonly used in water-based
drilling fluids sire barite, bentonite, lignite, and
lignosulfonate (Perricone 1980). A wide variety of
other materials are occasionally used, but these
account for about 90 percent of the total tonnage
of drilling-fluid additives.
Barite is a mineral consisting primarily of barium
sulfate. It is used to increase the density of drilling
fluid in order to balance and control the pressures
of the fluids in the rock formation being
drilled. Up to 700 lb of barite may be used per
barrel of drilling fluid.
Clay, most commonly sodium bentonite, is used in
drilling fluid. When mixed with water, clay exhibits
thixotropic characteristics: the resistance to shear-
ing forces in the fluid increases as the rate of shear
drops to zero. The gel that is formed helps sweep cut-
tings from the borehole. Bentonite also forms a
wall cake on the borehole, thereby reducing the loss
of fluids to the formation. Concentrations of 5-25
Ib/bbl are typical.
Lignosulfonates are commonly added to drilling
fluids to decrease viscosity. During the drilling
process the drilling fluid takes up fine solid materials,
increasing its viscosity. Adding water to adjust the
viscosity is generally avoided because this would
increase the total volume of the mud system and
require the addition of more barite. Lignosulfonates
act by controlling the flocculation of clay particles;
chrome lignosulfonates are most widely used. They
71-1
Milestones and resource potential of Bering Sea sales
Milestone
Bering-Norton
Sale 57
St. George
Sale 70
North Aleutian
Sale 75
Navarin Basin
Sale 83
Tract selection
Draft EIS
Public hearing
Final EIS
State comments
Sale
February 1980
June 1981
October 1981
February 1982
June 1982
September 1982
March 1980
October 1981
January 1982
May 1982
September 1982
December 1982
December 1980
August 1982
November 1982
March 1983
July 1983
October 1983
January 1982
October 1983
January 1984
May 1984
September 1984
December 1984
Estimated resources^
540 million bbl
1-5 billion bbl
700 million bbl
360 million bbl
*From Petroleum Information Package 1980.
1302 Summary and perspectives
function over a wide range of pH, soluble salt concen-
tration, and temperature. The chromium present
is all in the trivalent state in concentrations of about
2.5-4 percent by weight. Up to 15 lb of lignosulfo-
nate may be used per barrel of drilling fluid.
Lignite, a naturally occurring complex of waxes
and humic acids, is used generally to perform the
same functions as chrome lignosulfonate. However,
lignite does not perform satisfactorily over so wide
a range of conditions.
Other materials which may be used in water -base
muds are: polymers, e.g., carboxy methyl cellulose,
hydroxy ethyl cellulose, acrylamide, or xanthum
gum, may be used to increase viscosity and promote
filter-cake formation. Certain polymer systems can
be used to help increase bit life, improve penetration
rates, and reduce the tendency for the drillstring to
stick to the formation wall through differential
pressure; gypsum, lime, potassium chloride or other
salts may be used under some circumstances to
control formation damage; caustic soda may be used
to control pH, accelerating the thickening action of
clay particles and retarding corrosion; and
starch may be used as a thickening agent, which may
in turn require the addition of a biocide to control
bacterial growth. The chemical and physical charac-
teristics of some types of drilling fluids and seawater
are shown in Table 71-2, taken from Tornberg et
al. (1980).
Oil-base drilling fluids are used under certain con-
ditions in which water-base fluids will not perform
satisfactorily (McMordie 1980). Because of their
high cost and potential for environmental problems,
oil-base drilling fluids would ordinarily not be used
where water-base fluids would serve. The oil-base
fluids might be required under the following circum-
stances: for prevention of hydration in water-
sensitive shales, where hydration could result in
sloughing of material into the wellbore, stuck pipe,
and other problems; for drilling in salt formations
which would be soluble in water-base muds; for
high-temperature drilling which would cause chemical
breakdown of water-base fluids; and for acid envi-
ronments which would produce excessive corrosion
of the drillstring and casing.
Oil-base drilling fluids are generally made from
diesel fuel containing a small quantity of water or
brine in emulsion. Oleophilic colloids are used to
provide viscosity and thixotropic properties. Sur-
factants are used to help suspend barite and drilled
solids in the fluid. Because of the high cost of oil-
base drilling fluids, used oil-base drilling fluid and
associated oil-contaminated materials Eire customarily
returned to the supplier for processing and re-use.
At offshore locations the cuttings can be barged to
an approved disposal site or cleaned and discharged
to the sea floor with appropriate monitoring and
control, where this is permitted.
During the drilling process it is necessary to adjust
the chemistry and density of the fluids within opera-
tional limits. Increased volume resulting from these
additions requires periodic disposal of some of the
fluids in the water-based muds, but this seldom
happens when oil-base muds are used, since fresh
material must constantly be added as the well is
deepened. In offshore operations it is common
practice to dispose of fluid and cuttings directly to
the sea. Oil is always removed from discharge streams.
Sometimes when onsite disposal has been thought
to be potentially harmful the requirement for barging
of fluids and cuttings to an approved site has been
imposed. This type of disposal is inefficient, costly,
and possibly dangerous because of the requirement
for having standby barges on site when drilling.
Such disposal should be considered only when fully
justified.
The effect of drilling muds and cuttings on the
marine environment has been studied extensively in
the laboratory as well as in the field; the studies
have produced well over 100 publications, all but a
handful in the gray literature, related to the discharge
of these materials to the environment. The recent
symposium on "Research on Environmental Fate
and Effects of Drilling Fluids and Cuttings" held
12-21 January 1980 at Lake Buena Vista, Florida,
is by far the most complete documentation of this
topic, but there still is an urgent need for publica-
tion in conventional peer-reviewed journals that
would add credibility to the studies and eventually
remove much of the apparent confusion regarding
the real effects of these materials on the marine
environment.
The toxicity of the muds and cuttings has been a
subject of great concern. It is clear that different
formulations have varying toxicities for different
test organisms; agreement has not been reached
among investigators on which muds to consider for
testing, what kinds of organisms to use in the tests,
and, probably most important, how to translate
laboratory data obtained under essentially static
conditions to the relatively turbulent environmental
conditions of the ocean. Ninety -six -hour LC 50
values for drilling fluids of the type examined in
Table 71-2 above run between 4 and 70 percent:
the differences depend on the fluid and organisms
tested. The fluids typically used in deeper formations
(CMC/gel/resinex) tend to be more toxic than the
ones (CMC /gel) used in shallower formations, and the
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1304 Summary and perspectives
toxicity is greater for mobile species (mysids and
fishes) than for sedentary species (isopods, snails,
and polychaetes).
Trace metals, particularly chromium and cadmium,
which are present in drilling muds are of some con-
cern because of their toxicity and ability to progress
up the food chain cumulatively. Experiments con-
ducted so far in the environment (Horowitz and
Presley 1977, Crippen et al. 1980) have shown only
minor accumulation in sedentary organisms within a
narrow zone (few meters) around the discharge
plume. In laboratory studies mobile organisms such
as amphipods were able to purge accumulated trace
metals in about two weeks, even after exposure to
concentrations unrealistically high for environmental
situations.
The most important question in the problem of
drilling-fluid disposal is what the actual concen-
trations are that organisms might be exposed to under
natural conditions. Turbulent mixing in the ocean
under most conditions encountered will probably
dilute discharged fluids by a factor of 10-100 within
10-30 m of the discharge site. It would then appear
that any tests of the fate and effects of drilling fluid
must be done in the environment, preferably when
a well is being drilled, where all conditions can be
carefuUy monitored. Primary concern should not be
for acute effects, since these are unlikely, but for
long-term cumulative and subtle effects on the
biological community.
Oil spills
Considerable information is available on the weath-
ering and fate of spUled oil from both laboratory
studies and investigations conducted after accidental
spills. By extrapolating this information to the
Bering Sea environment, one can predict the fate of
an oil spill and estimate the resulting environmental
impact. As there are uncertainties in existing know-
ledge of the behavior of spilled oil, so too will the
resulting predictions and estimates be uncertain.
In the following discussion the most likely outcome
of an oil spill will be presented. In areas where un-
certainties are great, a "worst-case" estimate will
also be presented.
An accidental oil spill can occur at the sea surface
(tanker accident), at the seabed (pipeUne rupture),
or at any point from the seabed to the atmosphere
(platform accident or well blowout). Oil spilled at
the surface during ice-free conditions and far from
land might experience the following fate (based on
Jordan and Payne 1980).
Oil from a bulk surface discharge would spread
rapidly during the first 1-3 days. The extent of
spreading would depend on oil composition, avail-
able mixing energy, and competing surface processes
(evaporation, photo-oxidation, emulsification, etc.).
Spreading is retarded by loss of volatiles and water-
soluble components and by "mousse" (water-in-oil
emulsion) formation. Winds, waves, and currents
may cause the surface slick to drift over great dis-
tances. Evaporation is the principal weathering
process for surface oil, and most oil components
with 15 or fewer carbon atoms would evaporate in
the first few days after the spUl. Highly weathered
surface oil can break down into small lumps or tar
balls, the fate of which appears to be continuing
fragmentation to microscopic size.
Surface oil wiU be dispersed into the water column
by strong winds and breaking waves. Dispersion will
be enhanced by surface-active agents present in the
original oil or produced by photo -oxidation. The
presence of high concentrations (~200 mg/1) of
particulate matter can stabilize dispersions.
Aromatic hydrocarbons with three or fewer
rings have significant solubility in seawater, and
water-soluble fractions of crude oil are always
enriched in these compounds. Solubility is en-
hanced by turbulence and dispersion.
Oils containing high asphaltene and surface-active
material tend to form mousse under even gentle
turbulence. Mousse typically contains 50-80 percent
water and takes on a firm greaselike consistency.
Mousse formation retards evaporation, dissolution,
spreading, microbial degradation, photo-oxidation,
and association with suspended particulates.
Spilled oil can interact with suspended particulate
matter by adsorption or agglomeration. Dissolved
hydrocarbons have little tendency to interact with
particles, while dispersed oil can coat particles with
concentrations of a few hundred milligrams of oil
per kilogram of suspended matter. Such oil-coated
particles can serve as a mechanism for transporting
oil to the sediments. Copepods have been observed
to ingest small oil droplets and incorporate them
unaltered into their fecal pellets, which also sink
to the bottom.
Microbial degradation is an important removal
process, especially for dissolved, dispersed, and
adsorbed oil. Oil-degrading bacteria appear to exist
in all environments, but their numbers and activity
are enhanced in areas with a history of petroleum
contamination. In general, degradation rates are
lower for compounds which are multi-branched or
highly cyclic. The most resistant compounds may be
sulfur-containing hetero-atomic aromatic hydrocar-
bons and some highly cyclic alkanes (e.g., ho panes).
Degradation rates are enhanced by high inorganic
Environmental risks and research opportunities 1305
nutrient content, high temperature, and abundant
oxygen levels.
Oil weathering was studied extensively in three
relatively recent oil spills (Tsesis, Sweden, 1977;
Amoco Cadiz, France, 1978; Ixtoc-I, Gulf of Mexico,
1979). The results of these studies give some indica-
tion of the importance and rates of the various
weathering processes. Unfortunately, since not all
processes were studied at any one spill, results must
be pieced together to obtain the most complete
story.
The Tsesis spill
On 26 October 1977, the Soviet tanker Tsesis
struck a rock near the coast of Sweden in the north-
em Baltic Sea. About 1,100 mt of No. 5 fuel oil
were spilled, but cleanup operations were reported
to have recovered 700 mt. The remaining 400 mt
visibly oiled an area of 34 km^ . Analytical chemistry
studies after the spill (Boehm et al. 1980) demon-
strated rapid weathering. Within 10 days all of the
remaining dispersed oil in the water column was
severely altered in such a way as to suggest that
rapid microbial degradation of the aliphatic hydro-
carbons had occurred. Mytilus sp., a suspension
feeder, rapidly took up oil, and levels of more than
30 mg/g dry wt. of tissue were reported. Concentra-
tions decreased rapidly after one month, but only
after one year did total hydrocarbon levels approach
background. Even then, low concentrations of
specific petroleum-derived aromatic hydrocarbons
were detected.
Sediment traps were deployed to collect and inves-
tigate the hydrocarbon content of sinking particu-
lates. The material collected Was found to contain
large amounts of weathered Tsesis cdjcgo . Sedimenta-
tion of oil, high during the first two weeks of the
spill, was undetectable after two months. The
aliphatic hydrocarbons in the sediment traps had
experienced severe microbial degradation; the aro-
matic hydrocarbons appeared to have been lost due
to evaporation and dissolution processes. As much
as 7 mg of petroleum hydrocarbons per gram of
particulate was reported. No petroleum hydrocar-
bons were found in the surface sediment. This
puzzling finding led to the conclusion that the
freshly sedimented oil must exist at the sediment
surface in the form of a floe, which is easily dis-
turbed and lost by conventional sediment grab
samplers.
The fact that deposit-feeding Macoma sp. were
highly contaminated with oil confirmed the belief
that sedimentation must have occurred and that the
oil must have been deposited at the sediment sur-
face. Concentrations reached only 2 mg/g dry wt.
of tissue but remained at these levels for at least
two months. The hydrocarbon composition of
Macoma was nearly identical to that of sediment
trap material. Contaminated Macoma were found
outside the airea where visible slicks occurred, indi-
cating active subsurface transport of dispersed and
particulate oil.
Biological impacts (summarized by Linden et al.
1980) were described for pelagic, benthic, and
littoral communities. Limited data suggest that oil
concentrations in the water column reached 60 /ig/1
under an oU slick. Phytoplankton biomass and pro-
ductivity increased; species composition was un-
changed. Zooplankton were heavily contaminated
by oil droplets, but no reduction in standing stock
was noted. Total bacterial abundance increased in
the spill area. One month after the spill, measured
parameters of the water column were essentially
normal. Acute effects on fish could not be demon-
strated, although the possibility exists that an ob-
served decline in herring spawning in the area the
follovdng summer could be attributed to long-term
effects of the spill.
Calculations based on sediment-trap data revealed
that from 19 to 40 mt of oil sank. This oil at the
sediment surface caused no increases in mortality of
sedentary macrofauna, although mobile species were
reduced, possibly by emigration. Most meiofauna
groups showed abnormally low abundance in the
most affected area. The affected macro- and meio-
fauna had not recovered after ten months.
Mass mortality occurred among littoral crustaceans
and other Fucus-he\i macrofauna in areas where oil
slicks affected the shoreline. Considerable recovery
had taken place after 12 months, presumably the
effect of immigration from refuge areas which had
not been affected. Complete recovery of the littoral
zone fauna in two to three years can be predicted.
The Amoco Cadiz Spill
The Amoco Cadiz went aground off the coast of
Brittany on 16 March 1978. Over the next two
weeks its entire cargo of 223,000 mt of oil was
discharged to the sea. The large quantity of oil and
the proximity of the wreck to the shorehne (2.8 km)
caused great concern and reaction. About 40 percent
of the oil was in the volatile range and is assumed to
have evaporated. Even in the rapidly formed mousse,
the residence time of compounds with 15 or fewer
carbon atoms was determined to be five days or less
(Calder 1979). Microbial degradation did not appear
to be a significant process within the mousse, but
1306 Summary and perspectives
once oil was dispersed into the water column micro-
bial action was rapid, especially for alkane degra-
dation. Aminot (in press) reports depletion of
nutrients and oxygen over large offshore areas, the
result, he believes, of active microbial hydrocarbon
degradation. He calculates that up to 0.03 mg/l/d of
hydrocarbons were metabolized during the first 14
days of the spUl. Concentrations of oil in water
reached several hundred ^g/l under surface slicks in
coastal embayments, while concentrations offshore
varied from background (<2 /Jg/1) to 140 A/g/1 (Calder
et al. 1978). By May 3, water-column concentrations
had dropped to 60 /Lxg/l (Calder and Boehm, in press)
in embayments and 10 ^ig/l offshore (Berne et al.
1980).
An estimated 60,000 mt of oil reached the shore-
line. Oil that was not removed or buried was sub-
jected to physical and microbiological weathering.
Oiled tidal flats, which initially contained 1,000 ppm
of total hydrocarbons, showed rapid loss of hydro-
carbons for the first two months £ind then a slower
rate of weathering until about 95 percent was lost.
Petroleum hydrocarbons, especially certain aromatics,
were still detectable one year later (Calder and
Boehm, in press). Some oil which coated the shore-
line became encrusted with sand and other dense
material. Tidal action often removed the material to
the nearshore sediments. This phenomenon was
noted particularly in coastal embayments.
Organisms living in the fine sediments in coastal
embayments suffered the most significant damage.
Much of the toxicity was thought to be due to high
concentrations of dispersed oil at the time of the
spill. Millions of dead organisms were stranded on
the beach and the benthic biomass in heavUy oiled
areas may have been entirely destroyed. Recovery
has begun but is not complete and is particularly
difficult for at least one important food web amphi-
pod which does not have a pelagic life stage (Cabioch
1980).
Several commercially important species were
affected by the spill— how severely was difficult to
determine. Oysters cultured in coastal regions were
contaminated by oil. Although only a few were
reported to have been killed, 6,000 tons had to be
destroyed because they were inedible (Cabioch
1980). Some culture beds were reusable after
16 months, others not for more than two years even
with intensive cleanup attempts. Kelp reproduction
and density were normal after the spill, although the
biomass of red algae was reduced. Although signifi-
cant adult crustacean (crab, lobster) mortality was
not detected, the number of egg-bearing females was
unusually low in 1978 and 1979, indicating a poten-
tially reduced harvest in one or two future years.
Several fin diseases have been detected in flatfish
from heavily impacted areas, and plaice of the 1977
and 1978 year-classes were in low abundance in these
areas. It is estimated that the flatfish population will
not recover until the 1979 year-class matures.
The Ixtoc I blowout
The Ixtoc I well blew out in June 1979 with an
initial flow estimated at 30,000 barrels per day. The
blowout was not halted until March 1980, after a
total estimated release of 500,000 mt of oil. In
September 1979, a research effort was undertaken to
determine the major weathering processes acting on
the oil and to estimate rates of weathering. The pro-
jected technique was to conduct sampling at various
points along the north ward -flowing oil plume, relat-
ing measured compositional changes to estimated
time of environmental exposure. A hurricane passed
through the spill area just days before the arrival of
the research vessels, thoroughly disturbing the hoped-
for "steady state" oil distribution. As a result, many
of the weathering goals were not achieved. Prelimi-
nary research findings were presented at a symposium
in June 1980. The symposium proceedings provided
the following information.
The oU emanated from the sea floor at a water
depth of 51 m. The turbulence associated with the
release of the oU caused more extensive dissolution
of low-molecular-weight hydrocarbons than might
have resulted from a surface spill. Payne et al.
(1981) report benzene concentrations of 60-100 /ig/1
in and near the plume of rising oil; Brooks et al.
(1981) report volatile aromatic hydrocarbon concen-
trations of 50 jug/1 near the well, 9 jug/l at 6 miles
from the well, and 1 /ig/1 at 12 miles. Boehm
and Fiest (1981a) also note that the oil reaching the
surface appeared partially weathered by dissolution
and further that the surfacing oil was already emulsi-
fied and was "sticky."
Once on the surface, evaporation was the domi-
nant weathering process, with some dissolution
detected. Overton et al. (1981) presented evidence
for photo-oxidation, but only trace levels of phenolic
and carboxylic derivatives of hydrocarbons were
found in seawater samples. According to Boehm and
Fiest (1981a), chemical evidence indicates that
microbial degradation was not occurring in the
mousse, and Atlas et al. (1981) confirm that micro-
bial activity in the mousse was low and estimate
degradation rates of 5 percent per year from micro-
bial activity. It was postulated that limited nutrients
Environmental risks and research opportunities 1307
were responsible for the low observed rates, inasmuch
as the rates increased when nutrients were added.
Boehm and Fiest (1981a) find no chemical evi-
dence for microbial degradation in the water
column, even 44 miles from the well. Low nutri-
ent levels are thought to be responsible. Total oil
concentrations in the water column were reported
as 100-10,000 ppb; total alkyl benzenes and
naphthalenes were 0.5-500 ppb. The total amount
of oil within 25 km of the well in the upper 20 m
of the water column was estimated at 20,000 gal-
lons, or 1 percent of the total oil observed as sur-
face mousse. About 90 percent of the oil in the
water column was in particulate form.
Various authors present evidence of subsurface
"lenses" or "plumes" of oil which moved independ-
ently of the surface slick and which may have been
bounded by pycnoclines and frontal features. Data
to support these observations are limited. Boehm and
Fiest (1981b) deployed a few sediment-trap arrays
and collected sedimenting material which contained
from 1 to 2 Mg of oil per mg of sediment. They were
able to calculate a vertical flux of oil of
1-5 jug/cm^/d. The total suspended load at the time
of sampling was estimated as less than 100 iJLg/\ by
Boehm and Fiest (1981b) and as "low to non-
existent" by Nelson (1981). Previous laboratory
experiments indicated that several hundred /ig/1 of
suspended matter are needed to cause appreciable
sedimentation of oil (Jordan and Payne 1980).
Boehm and Fiest (1981b) also found low levels of
petroleum in sediments near the blowout. They
calculated that within a 30-km radius of the well,
about 1.5 percent of the total oil spilled could
be found in the sediments, which contained an aver-
age of 150 jug/g in the top 0.5 cm of sediments. They
estimated that more than 50 percent of the oil
existed £is surface material or as neutrally buoyant
particles (Boehm and Fiest 1981a).
Ross et al. (1981) reported that the mousse was
generally 1-3 mm thick and had a specific gravity of
0.99. They observed that the emulsion was viscous
and concluded that the use of chemical dispersants
was of questionable value in this instance.
Projections of the fate of oil spilled
in the Bering Sea
The preceding information can now be applied to
a potential Bering Sea oil spill. In the face of much
uncertainty and with many reasonable extrapola-
tions, the following mass balance can be constructed
for an offshore spill which does not affect a shoreline.
For purposes of this estimate, we will assume an
initial spill of 60,000 mt, which might be the cargo
of a medium-sized tanker. If the oil spreads to a
uniform 1-mm thickness, the maximum sea surface
affected would be 60 X 10*^ m^. For comparison,
the area of the middle domain in the southeastern
Bering is 2 X 10'° m^ . Therefore, the hypothetical
slick covers an area equail to 0.3 percent of the middle
domain. For the first few days, concentrations of
oil in the upper water column beneath the slick
would be on the order of 10^ ppb under mildly
turbulent conditions and 10^ ppb under greater
turbulence. Advection and dilution would reduce
these concentrations about one order of magnitude
for each 10 km from the discharge. Over the first
few days, the volatile components of the spUl would
evaporate. For a Prudhoe Bay crude, evaporation
would account for 45 percent, or 27,000 mt of the
hypothetical spill. The remaining oil may stay at the
sea surface, disperse or dissolve in the water column,
sink to the bottom, or be degraded by microbial or
photochemical action. Since very little photochemical
degradation was documented at the Ixtoc I spill,
we can assume that this process will be insignificant
at the higher latitudes of the Bering Sea. Microbial
degradation may be a more important process, per-
haps limited only by available nutrients.
The middle-shelf domain is the most nutrient-
poor region in the southeast Bering (Hattori and
Goering, Chapter 58, this volume) and in summer
contains an average of 3 /ig-at/l of NO3-N. If all of
this nitrogen were converted to microbial biomass
which conformed to the "Redfield Ratio" of 106 C
to 16 N, a carbon requirement of 20 Mg-at/1 would
exist. Assuming a 10-percent trophic efficiency,
200 /ig-at/1 of carbon would be ingested, which is
equivalent to 2,400 ^lg of carbon/1. If all of the
carbon came from petroleum, which is 80 percent
carbon, then 3,000 Mg of petroleum per liter would
be degraded by the exploding microbial population
before the nitrate was depleted and growth stopped.
If the microbial activity is constant in the upper 50 m
of the water column under the entire original surface
slick (60 X 10^ m^ ), a potential exists for microbial
degradation of 9,000 mt of oil, which is 15 percent
of the original spill. This projection is optimistic and
probably represents an upper limit. The lower limit,
of course, is no microbial degradation. The cal-
culated consumption of oil in the English Channel
after the Amoco Cadiz spill was 0.4 mg oil/1 before
nutrients were depleted, which projects to 1,200 mt
of oil degraded in this scenario, or 2 percent of the
original spill.
Sedimentation of the spilled oil could be an
1 308 Summary and perspectives
important process. A very low sedimentation rate
was observed at Ixtoc, only 1 fxg oil/cm^ /d (Boehm
and Fiest 1981b). At this rate over the area of the
hypothetical spill, sedimentation of 0.6 mt of oil per
day would occur, or 0.1 percent of the original oil
per day. Given the sluggish circulation in the south-
east Bering, the slick might hover over a given portion
of the seabed for 30 days. This circumstance would
place 30 jug of oil/cm^ of seabed under the slick.
If all the oil remained in the upper 0.5 cm of sedi-
ment, which has a density of 4 g/cm^ , a concentra-
tion of 15 iJg/g (ppm) of oil would result. One could
argue that sedimentation would be much greater in
the Bering than at Ixtoc because of higher loads of
suspended matter— for example, 1-5 mg/1 in the
northern Bering (Feely et al.. Chapter 20, Volume
1. A tenfold increase in sedimentation would cause
the removal of 30 percent of the original hypothetical
spill and result in surface-sediment oil content of
150 ppm.
At this point, we have accounted for 45 percent of
the spill by evaporation, 2-15 percent by microbial
degradation, and 3-30 percent by sinking. There
remains 10-50 percent unaccounted for, which we
will assume is converted to tar balls or microparticu-
lates and is dispersed to undetectable levels after
30 days. It is disappointing not to be able to create
a better mass balance, and yet even the foregoing
permits a first approximation of the expected eco-
logical impact.
Estimated ecological impact from a spill
in the Bering Sea
The seabirds would be the first noticeable casual-
ties of an offshore spill. Bird distributions are patchy
and unpredictable, but existing data (Hunt et al.
Chapter 38, this volume) indicate 10^ birds/km^ as
an upper-level average density. Discounting avoid-
ance behavior, we can assume that all seabirds in the
path of the spreading oil slick will be killed. The slick
occupies 60 km^ and therefore 60 X 10^ birds would
be immediately killed. More birds may become en-
trapped by the slick as it moves airound for 30 days
before losing its coating ability , and it is possible that
a large flock (10^ birds) may be affected. Estimated
bird mortality is therefore 10^-10^ birds, or less
than 1 percent of an estimated summer population
of 10' birds.
Some marine mammals— northern fur seals, for
example— will probably be killed. A quantitative
estimate is not possible from existing data, but it
seems unlikely that more than 10'^ mammals could be
affected during an offshore spill. This level of impact
should have no ecological significance.
The evidence from the Tsesis spill indicates that
microbes, phytoplankton, and zooplankton were
not severely affected during the spill and that ob-
served deviations from normal had been corrected
within 30 days. There is no reason to expect any
different response in the Bering Sea.
Concentrations of oil in water observed at Ixtoc
decreased from 10 to 0.1 ppm within 20 km down-
stream of the well (Fiest and Boehm 1981). Con-
centrations of oil in water in coastal embayments
fell below 0.1 ppm within 30 days after the Amoco
Cadiz spill (Calder et al. 1978). Concentrations
below 0.1 ppm were measured less than a week after
the Tsesis grounding (Kineman 1980). A water-
column concentration of 0.1 ppm or greater per-
sisting for 30 days after a Bering Sea spill could be
lethal to subadult stages of shrimp, crab, and fish,
although the evidence for such an impact is derived
from a variety of laboratory studies that cannot
accurately reflect real conditions. If all pelagic
species or life stages are distributed uniformly in the
middle domain of the southeast Bering, and all
organisms beneath the original oil slick (which occu-
pies 0.3 percent of the middle domain— see above) are
killed, only 0.3 percent of the population is lost,
which seems insignificant in an ecological sense. The
affected populations should recover within one
life -cycle.
Similarly, 0.3 percent of the middle domain
sediments would receive oil concentrations of 15 to
150 ppm. If, as happened in the Tsesis spill, the
oil resides on the surface floe, its effective concen-
tration may be much higher, and lethal effects should
be expected on amphipods and meiofauna. An ex-
perimental study in lower Cook Inlet demonstrated
that after a year, most of the oil had been lost from a
sediment initially containing 100 ppm of oil (Payne
et al. 1980). We should expect benthic recovery to
begin within a year after a spill in the Bering Sea and
become complete within a few years at most.
Although the above impact estimates are based on
assumptions and tenuous extrapolation, they seem
reasonable in the light of observations after several
oU spills. One must conclude that the Bering Sea
would not suffer significant impact from such a spill
as is described here. A greater impact would no
doubt result if the oil spill reached the coastline or
the ice-edge.
A spill of 60,000 mt of oil could easily produce
adverse effects on 100 km or more of shoreline. In
the southeast Bering it would be difficult to find that
much shoreline which did not contain a salmon
Environmental risks and research opportunities 1309
stream, mammal rookery, bird colony or feeding
area, or other ecologically important feature. Given
the number of important coastal targets and the
logistic difficulties associated with working in remote
areas, it is unlikely that any action could be taken to
prevent coastal impact of a nearshore spill . Oil
could persist on a coastline for 1-10 years, depending
on several conditions, and yet eventually the coast-
line would recover. Organisms below the top preda-
tor level have relatively short regeneration times and
can repopulate an affected area from refuge or
unaffected areas once natural processes reduce oil to
non-lethal levels. Certain top predators (birds,
mammals) could suffer long-lasting, population-
level effects if an oil spill reached a few critical
habitats. Although identification of such habitats
is beyond the scope of this chapter, it is clear that
only a few of the known rookeries and colonies are
truly critical in an ecological sense. Once these
critical areas are properly identified our best efforts
must be employed to protect them from oil-spill
damage, even if that means leaving known oil re-
serves untapped.
Research and actions needed to minimize
environmental risk from oil spills
The above discussion highlights a few research
needs critical to determining the potential for en-
vironmental damage from oil spills in the Bering Sea.
Subjects needing further research are:
a. Transport of oil to the benthos. The proc-
esses which control sinking of oil must be
better understood, their efficiencies deter-
mined, and reliable estimates made of quanti-
ties of oil which would reach the benthos
under a variety of circumstances. Such
information is especially critical in the Bering
with its valuable benthic and demersal
resources.
b. Recovery of oil-contaminated environments.
All environments can recover from an oil spill.
Only the rate of recovery is not known.
Determination of oil degradation and environ-
mental recovery rates for key environments
(e.g., benthic, shallow sub-tidal, intertidal)
and for critical locations (e.g., rookeries
or hauling grounds, low-lying bird colonies)
will be necessary before the potential for
environmental impact can be estimated.
Loss of organisms present at the time of
initial oil contamination may be acceptable if
the environment recovers in a reasonable time
and the lost populations are replaced.
c. Effect of use of dispersants on a. and b.
above. Chemical dispersants should be used
only if chemicEilly dispersed oil will have
less adverse effect on the environment than
nondispersed oil. At present there are no
good data from which one can determine
whether the use of dispersants affects oil
transport to the benthos, reduces total
environmental impact in nearshore areas,
or affects environmental recovery rates.
d. Long-term cumulative effect of multiple
spiUs and chronic discharges. The ability
to detect low levels of hydrocarbons and
especially their metabolites is constantly
improving, and we know that hydrocarbons
are ubiquitous, even in the Alaskan outer
continental shelf. It seems certain that
background levels of hydrocarbons will
increase in the Bering if oil production occurs
there. Continued vigilance is required to
ensure that we become aware of potential
impacts, presently unforeseen.
In addition to the above research needs, there are
several actions which government and oil industry
should take to reduce the environmental risk from
oil spills. These are:
a. All known safety features must be incor-
porated in the procedures involved in explora-
tion, production, and transport phases of oU
and gas extraction. Even with today's stan-
dards, there are still many inexcusable "acci-
dents" which could have been prevented.
Any tankers used in the Bering should be
required to have double bottoms, redundant
propulsion, steering and navigational systems,
and a complement of exceptional officers and
crew. Pipeline leak detection and surveillance
systems need improvement.
b. Spill contingency plans must be developed,
equipment procured, and personnel trained
to deal effectively with oil spills in the remote
environment of the Bering Sea. In partic-
ular, supplies needed for mitigative action
and for the health, safety, and comfort of
personnel should be stockpiled and adequate
airlift capability identified. Large aircraft,
properly equipped for dispersant application,
should be acquired, probably by the Coast
Guard, if the use of dispersants is demon-
strated to be valuable.
c. A capability for real-time tracking and fore-
casting of oil-spill movement must be devel-
oped so that spill-response organizations can
1310 Summary and perspectives
anticipate where action will be needed on a
daily and weekly basis.
d. Scientific investigation of environmental
damage must be initiated within the first
week after every major spill (>100 bbl).
From such studies one can determine the
real impact of oil spills. This knowledge will
be useful in litigation, for improving spill
countermeasures and for developing regula-
tions for future industry activities. The
industry-sponsored study of damage from the
Amoco Cadiz spill and the government-
sponsored Ixtoc damage-assessment study
were not begun until more than a year after
the spills. Because of this delay, the results
of these studies will be incomplete and open
to question.
e. A substantial part of the money from lease
sales should be set aside in a fund to support
research on the effects, prevention, and
mitigation of oil spills and for such activities
as described in b, c, and d above. Industry
should also develop a fund, based on produc-
tion volume, which can be drawn upon during
and after a spill for mitigation, cleanup,
scientific investigation of environmental
damage, and related activities. The industry
fund should be held in tax-free escrow,
replenished when used, and returned to
industry accounts when production ceases.
f. Industry and government should accept the
condition that an area, once oiled, must be
protected from additional oiling during the
recovery period by suspending production,
rerouting tankers or pipelines, or taking
other appropriate measures. A second oiling
during the recovery period would be more
pernicious and could eliminate survivors of
important populations and significantly retard
or perhaps prevent recovery. This is an
unacceptable risk.
FUNDAMENTAL RESEARCH OPPORTUNITIES
It would be a serious oversight indeed if in our
deliberations about how to minimize the risks from
oil and gas development we were not to indicate the
importance of fundamental research as a necessary
tool in all scientific endeavors. Such research leads
to understanding from which approaches to mitiga-
tion and control may be taken. In fact, one wonders
if any scientific effort is justified unless it in some
way adds to the reservoir of knowledge that leads
to understanding. More specifically, satisfactory
solutions to environmental problems in the oceans,
especially those where impact from contaminant
discharge is of concern, can come only from a
thorough understanding of how the ecosystem
functions in its natural state.
The eastern Bering Sea shelf is perhaps as well
understood as any continental shelf in the world as
documented in these two volumes. To use this
strong interdisciplinary base for continued investiga-
tions of a subarctic continental shelf represents a
unique scientific research opportunity. The authors
of the 70 preceding chapters of this book have
in turn dealt with the areas of deficiency in knowl-
edge pertaining to their particular interests. It would
appear constructive at this time to draw upon these
many offerings and upon workshop deliberations
that were held as part of the preparation of this
book to indicate broad areas where investigation of
yet unanswered questions about the Bering Sea
shelf is needed. What some of these questions are, as
now seen, and how they might be solved is the
subject of this final section of this chapter. The
authors approach this topic with considerable trepida-
tion, but fully realize that "nothing ventured, nothing
gained" applies even to scientific research.
Probably man's greatest concern about the Bering
Sea shelf is its fishery resources. Therefore the most
important questions we can ask about this region
concern the fishery resources and their predicta-
bility. On the basis of information presented in
Section V, edited by Felix Favorite, and Section XI,
edited by Murray Hayes, it appears that reasonably
good assessment of harvested and potentially harvest-
able fish stocks exists for the ezistem Bering Sea shelf,
but that far less than adequate information exists on
the ichthyoplankton, juvenile stages, and trophic
dynamics of these same fish species. Studies of this
subject belong to the field of fisheries oceanography.
It is important to realize from this terminology that
the oceanography to be done must relate to signifi-
cant events that occur within the fish population.
For instance, since most of the nekton have an
average life-span of more than one year, short-term
variations on a scale of hours or days might be
thought to have no effect— the nekton components
and demersal ichthyoplankton tend to integrate
these events. It might be inferred, then, that oceano-
graphic studies of the first priority should be made
over a time scale which the organisms cannot inte-
grate. Such a conclusion may, however, be erroneous
because the very survival of the juvenile nekton
components, because of specific food requirements,
may depend on an event or events in the plankton
community controlled by short-term phenomena.
Environmental risks and research opportunities 1311
To predict the success or failure of a spawning popu-
lation, such events must also be understood and
predicted.
Hypotheses must be formulated in terms of species
assemblages, individual species, or sub-groups within
a single species. Resolving problems and proving or
disproving hypotheses probably should start at this
level and fan out to include the energy transfer at
lower trophic levels and eventually the physical-
chemical environment itself. Phenology or timing
of events is crucial to a fish from egg to adult as it
moves from one environment to another linked in
time and space.
Predictability will probably best follow as a result
of an inquiry system that attempts to examine the
environment of the nekton in a holistic way, so that
not only the organisms and their trophic relations
are defined, but the energy flow as well. The best
example of such an approach is represented by the
PROBES (Processes and Resources of the Bering
Sea Shelf, See Section X, this volume) studies now
under way in the southeast Bering Sea. This effort,
now in its fifth year under the sponsorship of the
Office of Polar Programs of the National Science
Foundation, is an attempt by an interdisciplinary
team to relate the physical processes and biological
events at all trophic levels and to determine the
dynamics of the system that provides for energy
fixation to maintain the enormous biological pro-
ductivity of the Bering Sea shelf. From these data
sub-models can be constructed, of which the carbon
trophic -level budget described below is an example
of a first crude effort, followed by much more
comphcated predictive models as data and techniques
become available.
Because of the nature of the ecosystem supported
by the ocean, predictability of one biological com-
ponent requires a high level of understanding both
qualitatively and quantitatively of the whole. Thus
it is implied that to be able to predict any component
of fisheries all components of the ecosystem must
be predictable. If such understanding were possible,
then the production of predictive models would
be a relatively easy accomplishment. For the immed-
iate future, however, scientific advance in understand-
ing ecosystem dynamics will probably have to move
one segment at a time as opportunity presents itself.
As information is accumulated and rehable subset
models can be constructed, combined, and inter-
faced, the ultimate goal of ecosystem predictive
models may evolve.
There are many scientific problems about the
Bering Sea shelf which are by the nature of the
system important to fisheries, but which are also
important in themselves. Some that are easily identi-
fied will be mentioned here. Many more, known and
unknown to the authors, remain to be identified by
others.
Ice
Ice is an important physical feature of the Bering
Sea (see Sections II and VII). The eastern Bering
Sea shelf is a relatively shallow (shelf break at a
depth of 150 m) but broad (ca. 500 km) region
that is seasonally ice covered in varying degrees,
depending upon winter conditions (see Fig. 44-1).
During a typical winter, the ice advances on the order
of 1,000 km toward the south from the Bering
Strait to the shelf break, primarily by freezing sea-
water within the Bering Sea and not from extensive
advective transport through the strait. The ice pack
is in a continuous process of formation and melting.
Estimates of the replacement are on the order of
3-8 times each season, depending on conditions.
In spring about 63 percent of the ice melts within
the basin, and the remainder leaves the basin through
passes to the south and the Bering Strait to the
north. The dynamics of formation and movement
of this offshore ice and its shorefast counterpart
creates hazardous conditions for offshore oil and gas
development, influences the hydrographic regime of
underlying waters, and markedly influences the
cUmate of the entire northern hemisphere. Ice is
clearly important in the physical heat budget of the
ocean and atmosphere. Less obvious, but of con-
siderable importance, is its influence on primary
production, not only within the ice regime (where
10 percent of total productivity occurs), but by its
sustained effect on hydrography and associated
bio tic responses over the entire shelf region.
The influence of ice on biological and physical
events might better be examined on the Bering Sea
shelf than on other shelves of the boreal region
because of the vast amount of relevant data now
available and continuously being collected.
Important unsolved problems regarding Bering Sea
ice remain to be investigated. A better understanding
of the thermodynamics of the concept of ice as a
southward-moving conveyor belt (replacing ice
between 2.5 and 10 times each ice season) of Pease
and McNutt (Section II, Chapters 10 and 13) needs
further evaluation in order to better understand ice
trajectory, influence on heat budget, and influence
on productivity. The coupling of ice-related phyto-
plankton growth to higher trophic forms needs to
be evaluated in terms of the extent and intensity of
annual ice cover, the location of ice bloom, and
associated biota such as mammals and birds. Results
1312 Summary and perspectives
of such studies would help determine the dependency
of biological events of the shelf area on ice condi-
tions and history and are necessary for completing
carbon and energy budgets on which predictive
models depend.
In the area of ice physics many important ques-
tions need to be answered. The problem of the shear
structure of ocean currents immediately underneath
ice and how this affects transport of sediments,
detritus, or more practically, spilled petroleum needs
to be resolved. Ice gouging is a phenomenon of
importance to understanding structures on the sea
floor, sediment transport, and sea bottom topography.
To better understand this phenomenon the relation-
ships between ice sheet thickness, maximum sail
height, and keel depth of ridges must be known.
Furthermore, some relationship between ice-flow
velocities and velocity of water due to tides, currents,
and winds needs to be established.
Geology and geophysics
Geologically and geophysically the most critical
information gaps in the Norton Sound area, where
most of this type of work has been concentrated
in recent years, are the areas of active faulting,
liquefaction, and possible areas of gas-charged
sediments. The location aind identification of active
(Holocene) faults have not been addressed, although
seismicity data show frequent, relatively low-level
seismic activity in and around Norton Sound. These
data have not been correlated with mapped faults.
The difficult problems involved with gas-charged
sediments (Kvenvolden et al. Chapter 26, Volume 1)
are in need of resolution. It is most important to
determine exactly where anomalies observed in
high-resolution seismic records are and whether
they come from deep thermogenic or near-surface
sources. Multi-channel data on closer seismic lines
and vibracore sampling followed by gas geochemical
analysis should resolve the location, origin, ranges of
gas saturation, and occurrence aind extent of
cratering; but yet to be determined are the mech-
anism of the gas-charging phenomenon, changes in
pore-pressure during storms, and cyclic wave loading.
A detailed sediment budget of the Yukon River
is not available, but is currently under investigation.
It is difficult to evaluate other sediment budgets
(and also carbon budgets) of the area without high-
quality Yukon River data. Understanding the sedi-
mentation regime of the area will help overcome the
great difficulty encountered in dating observed faults,
since the surface sediments are continuously being
resuspended, transported, and eroded, making
*"€- or ^'°Pb- dating technology difficult to apply.
Chemistry
Many important questions in chemistry remain
unanswered, but most of these are directly related to
larger oceanographic questions of ecosystem dynam-
ics. Carbon and nutrient budget questions are impor-
tant in ecosystem studies because they provide
a means to integrate the activities of communities
on a quantitative basis, thus allowing a useful check
on independent studies of components of the eco-
system—an important control on other more specific
analyses. Several important parts of the cycle of
carbon in the ecosystem are still not weU under-
stood. The flux of carbon to the benthos (detrital
cycle) and sediment interface has not been estimated
quantitatively. Related studies should focus on
transport of materials from the surface to sediments
and atr-sea gas exchange.
Other chemical studies of importance concern
the utilization of trace metals by biota, remobiliza-
tion of heavy metals from the sediments, nitrogen
fixation and denitrification rates, rates of utiliza-
tion of organic carbon by microorganisms, and
difference in carbon cycle in areas of high macro-
phytic carbon and areas where phytoplankton pro-
vide the major source of carbon.
In this treatise data are presented which can be
used to estimate the standing stock of most of the
important organisms that make up the biomass of
the Bering Sea shelf. In addition, some data are
given on feeding rates, growth rates, and food-web
dynamics. It now appears possible to make an ini-
tial estimate of the amount of organic carbon neces-
sary to support the biota of some trophic levels of
certain parts of the shelf. Two areas are chosen:
the outer domain (See Fig. 5-8), which lies between
the 100-m and 200-m contours and extends from the
Aleutians to the Pribilof Islands, covering an area
of 1 X 10"* km^ , and the middle domain, bounded
by the 100-m and 50-m contours, extending from the
Alaska Peninsula to a line between St. George Island
and the south end of Nunivak Island, and covering
an area of 2 X 10" km^ . Breaking the shelf area up
into smaller segments in this manner was not free of
difficulties since some of the resource data are not
specific enough to be so isolated, and the continual
seasonal movement of some animals makes it diffi-
cult to allocate residence time to any one region. The
advantages seemed to outweigh the disadvantages,
however, because dealing with the areas where most
is known about all trophic levels will lead to finding
out earlier where knowledge is insufficient and thus
will guide subsequent investigators to significant
problems.
Environmental risks and research opportunities 1313
The results of our effort to estimate the primary
fixed organic carbon required (primary production)
for some of the outer-domain fauna are presented in
Table 71-3 and for the middle domain in Table 71-4.
Resource data for these computations were mostly
taken from this book, as referenced in footnotes
to the tables.
Of the factors used to reduce wet weight of organ-
isms per unit area to primary carbon required, the
trophic factor is the most uncertain and also the
most influential. To obtain this factor, food-web
data (Feder and Jewett, Chapter 69), which in their
present form are only qualitative, were used to esti-
mate the relative amount each species consumed of a
particular trophic level. The factor was then esti-
mated by allowing those organisms (zooplankton,
etc.) which feed on phytoplankton or organic detritus
to have a value of one, those feeding on zooplankton,
euphausiids, and the like a value of 10 (reflecting that
unless better data are available, as they are for zoo-
plankton, 10 grams of food are required to produce
1 gram of body mass), and organisms consuming fish,
which feed on zooplankton, etc., a value of 100. For
many organisms, such as pollock, which are some-
times cannibalistic, or other top carnivores, this
factor rises to 1,000, a factor of 10 more than the
trophic factor for the food organisms. The trophic
factor used also depends upon whether the food
requirement data are given as grazing rate or growth
rate. Grazing-rate data are multiplied by the trophic
factor of the food consumed. Growth -rate data must
be multiplied by a factor related to efficiency of
assimilation in order to relate growth to primary
carbon requirements.
The data presented in Tables 71-3 and 71-4 contain
some interesting and sometimes surprising informa-
tion. The zooplankton and micronekton data in both
the inner and outer domain appear to support reas-
onably well the present thinking of the plankton
ecologists (Section X) that the outer-domain phyto-
plankton are heavily grazed by the zooplankton
community (55 percent), whereas in the middle
domain a much lower percentage (7.5 percent) is
grazed, leaving most of the production available for
formation of detritus and subsequent support of the
benthic community. The walleye pollock data also
seem reasonable if the lower stock assessment
(2.5 g/m^ ) of Smith, Chapter 33, is used for the
outer domain: pollock would require 27 percent
of the estimated primary production. If the higher
value (10 g/m^ ) were used, the requirement would
exceed 100 percent. In Smith's calculation of required
primary production (Table 33-8) no trophic factor
was used to estimate the primary carbon required to
produce a unit mass of pollock. Had the same
trophic factor been used, the results would be the
same as presented here. The infauna and epifauna in
both domains show a very high requirement. These
could be on the high side because of high biomass or
grovirth-rate estimates, but in view of the exten-
sive data presented in Chapter 69, it appears that
the estimates of primsiry carbon requirements are
reasonable.
Marine birds, many feeding at the top predator
level, take a heavy toll of production in both do-
mains. The murres, with a concentration of over
1.5 million birds around St. George Island alone,
represent only a relatively small part of the total
bird population of this area and yet consume around
5 percent of the estimated primary production.
This estimate is probably low and is expected to be
revised upward as data are more carefully analyzed.
The marine mammals, represented here by fur
seals in the outer domain and walrus in the middle
domain, are difficult to evaluate in terms of primary
production requirements in a limited area because
they move about seasonally and in a different pattern
annually, depending on the weather conditions. The
conservative estimate made here, however, shows
the fur seal alone in the outer domain to consume
about 40 percent of the primary production and the
walrus in the middle domain about 5 percent, or
about the same as the estimate for murres. Surprising,
too, is the calculation that the known commercial
fish catch for the outer domain would require more
than the estimated primary production to produce.
These two tables represent an effort to tie
together what is presented in these volumes about
carbon requirements for maintaining some of the
biomass of the middle and outer domains of the
eastern Bering Sea shelf. The numbers do not add up
to balance the contribution of primary production
and the requirements of animals. Perhaps, however,
a more precise balance should not be expected, in
view of the difficulty of obtaining reliable data for
such computations. Further refinement of the data
and means of calculating the carbon requirements
should soon lead to use of techniques similar to this
to evaluate more accurately than is now possible the
partitioning of carbon in the ecosystem. The above
data do suggest that the primary productivity values
used in these computations may be low. In fact.
Hood (Chapter 22, Volume 1) and recent unpub-
Hshed data (Iverson and Goering; Codispodi and
Hood) obtained during the 1980 field season ind-
icate that present estimates should be revised upward
substantially.
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1316 Summary and perspectives
Transport
Physical oceanography of the Bering Sea has pro-
gressed from large spatial and temporal scales in the
deep Bering Sea, which followed from the available
background information, instrumentation, and scien-
tific research resources formerly available, to measure-
ment of the small-scale phenomena required to under-
stand the broad -scale events. The small-scale studies
have been greatly enhanced by hydrographic pro-
files which have increased vertical resolution tenfold.
Horizontal resolution has been increased propor-
tionately by ample shiptime dedicated to studies of
physical structure and dynamics. An abundant use
of current meters associated with intensive hydro-
graphic studies, often on a time-series basis, has led to
a high level of understanding of transport rates and
establishment and maintenance of frontal systems,
and in general to a far more precise conception of the
forces of the physical system which heavily influence
or control the biological environment.
Even as late as 1972 (Hood and Kelley 1974),
representations of the current system of the Bering
Sea showed a counterclockwise current flowing
through Bristol Bay which originated from transport
of Gulf of Alaska surface water through Unimak or
more western Aleutian passes. This water allegedly
swept over the shelf to the north to help form the
well-established flow through the Bering Strait.
Investigations over the past decade have refuted the
existence of this shelf current, but have established
the presence of three permanent oceanic frontal
systems located roughly on the shelf break, at the
100-m and at the 50-m depth contours. Transport
across these fronts is very limited, and a slow drift of
1-2 cm/sec parallel to the fronts in a northerly
direction has been observed. A slope current does
transport water northward in the Bering Sea seaward
of the shelf-break front, where part of it flows west
of St. Lawrence Island to help form the Bering Strait
current. A coastal current along the west coast of
Alaska which transports much of the water of the
Yukon and Kuskokwim rivers joins this current before
it enters the Chukchi Sea through the Bering Strait.
Much of the success of transport studies on the
Bering Sea shelf can be credited to the closely inte-
grated interdisciplinary studies that have come from
scientific interest in answering important questions
about how the ocean functions as a system. An
interdisciplinary team studied the system in unison,
and thus the work of each investigator supplemented
the simultaneous data of others. For example, as a
result of the elucidation of the frontal system on the
southeast shelf region, an explanation of whale
migration, the concentration of bird populations, and
the patterns of commercial trawl fishing along the
shelf-break front became more apparent: the physical
regime supports a closely coupled energy flow to the
pelagic system upon which whales, birds, and some
fishes depend. Likewise, the bottom fisheries for
sole, tanner crab, and king crab and the popula-
tion concentrations of walruses are found at the
middle front and in the middle domain: this regime
is physically controlled so that it does not support a
large grazing zooplankton community and therefore
allows fixed carbon, mostly in the form of organic
detritus, to reach the benthos, where it is utilized by
a large infauna and epifauna population, which in
turn supports these bottom-feeding organisms.
Although remarkable progress has been made in
transport studies, many questions yet exist and
offer outstanding research opportunities to help
understand shelf dynamics in general and the Bering
Sea shelf in particular. One of the most important
questions is related to the rate of supply of nutrients
to the three domains that provides for extended
periods of high rates of primary production on the
shelf. The middle domain has the highest produc-
tivity (400 gC/m^/yr), the outer domain has less
(200 gC/m^ /yr), and the inner domain has the
least (120 gC/mVyr).
There are several more questions. What is the
relation between tidal energy, wind energy, and other
physical features in maintaining the frontal systems?
What is the relation of water flow to ice transport and
dynamics? What are the energy relations of ice to
annual hydrographic regime on the shelf? Many
other studies need to be continued: we need enough
further hydrographic and current data (particularly
major flow) to serve as the regional framework for
modeling and process studies and more temporal
coverage of variability in hydrographic structure in
order to estimate flushing rates and distribution of
pollutants, to describe seasonal progression of biolog-
ically important properties, and to serve as input to
numerical models on turbulence.
Plankton ecology
There have been extensive studies of carbon pro-
duction rates over much of the ice-free region of the
Bering Sea shelf, accompanied by nutrient, chloro-
phyll, and phytoplankton distribution measurements,
especially on the southeast shelf region. Regions of
high production are related to the position of oceanic
frontal systems where these fronts dominate the
characteristics of the phytoplankton growth pattern.
At the outer front and outer domain, spring blooms
are largely grazed in the water column by early de-
velopmental stages of large overwintering zooplank-
Environmental risks and research opportunities 1317
ton (e.g., Calanus cristatus and C. plumchrus). At
the mid-shelf front and in the middle domain most
plants produced during the spring bloom are believed
to sink to the benthos. Ice, which covers most of
the region during the winter, has associated phyto-
plankton blooms of short duration as it recedes.
About 10 percent of the productivity of the shelf
is associated with this phenomenon.
Zooplankton have been collected extensively
over many years and there appear to be sufficient
data to describe biomass and major species groupings
for the whole of the Bering Sea. The association of
these organisms with the frontal systems is of great
importance to energy transfer relationships. In the
oceanic domain production of zooplankton is esti-
mated to be 1-27 gC/m^ /yr, 33 at the shelf break,
8 in the mixed zone (middle domain), and 2 in the
inner domain. It is possible that these results, par-
ticularly in the inner domain, are imprecise, since the
turnover rates of organisms with short generation
times have not been carefully considered.
Many opportunities for research in plankton
ecology are apparent from evidence now available
in this and other related publications. Probably the
age-old problem of plankton patchiness can best be
addressed here because of the wealth of basic infor-
mation now available. Success in this area will
require careful integration of the physics and chemis-
try with plankton dynamic studies. The physics
of the system will determine the stability of the
bloom configuration and the limits of dispersion
which will control the concentration of stimulating
or inhibiting chemical compounds that influence the
bloom phenomenon. Trace-metal chemistry, which
has largely been neglected in these studies in recent
years, and organic chemistry of the media in which
the bloom occurs should be fruitful in supplying
some of the reasons for bloom formation and demise,
and in explaining the patchiness well enough that it
might eventually be predictable. The importance of
these studies, in addition to their academic interest,
is in the relation of patchiness of food organisms to
survival of larval fish and population distribution
of benthic infauna.
In the middle domain of the shelf, according to
PROBES hypothesis, the phytoplankton are not
heavily grazed, but sink to the bottom as food for
benthic organisms. Although this hypothesis has
considerable support (Table 71-4 and Chapter 57),
there have been few studies attempting to deter-
mine the actual existence of detritus on the surface
sediments, its fallout rate and composition, or in
fact the nature of the benthic food cycle as related
to overlying water-column conditions. How this cycle
may be altered by pollution during oil and gas devel-
opment activities may be one of the most important
considerations in transport of petroleum hydro-
carbons to the benthic community. Only adsorption
to detritus (organic or inorganic), transport by fec£il
pellets, or sedimentation of weathered oil by direct
fallout are reasonable mechanisms by which such
material can reach the benthic biota. Of these, in
the middle domain, the association with organic
detritus appears to be the most potentially
important.
Euphausiids are found in large populations over the
shelf, particularly at the outer front. Their abundance
and fluctuations in population levels have not been
quantified, although some acoustic and net surveys
have been initiated. Studies on feeding strategies and
biology of these organisms are needed since they
are important food for mammals, birds, and fish.
A greater opportunity to carefully evaluate the
heretofore accepted, but now questioned, methods
of measuring primary productivity in the ocean
exists for the Bering Sea shelf than perhaps for
any other part of the ocean. Independent estimates
by carbon budget, '"C uptake, nutrient uptake,
nutrient supply, and biomass requirements should
all give comparable results. Such estimates have not
been made elsewhere, but because of the present
understanding of the Bering Sea shelf system, they
are now a viable and exciting possibility in this region
of the ocean.
Marine mammals
Because of the very large populations of many
kinds of marine mammals in the Bering Sea and their
heavy requirements for food, they are one of the
dominant features of the ecosystem. Since these
animals have a demand of several times more primary
carbon than the commercial fisheries and are essen-
tially protected from harvesting, except for subsis-
tence hunting by native peoples, they are of consider-
able importance in the management of commercial
fisheries. The lack of quantitative data on numbers,
biomass, food dependence and efficiency of utiliza-
tion, foraging pressure, and behavioral responses of
many of these animals makes existing management
strategies questionable.
The walrus population (Lowry and Frost, Chapter
49, this volume) may be under stress due to increas-
ing numbers, but because little is known about the
feeding patterns of walruses, e. g., time in water vs.
time on ice, it is difficult to obtain accurate survey
data. More perhaps could be learned under the
present circumstances about physiological stress in
these animals by monitoring the subsistence harvest
1318 Summary and perspectives
than in any other way. There is a further need for
evaluation of benthic food animals taken by the wal-
rus over many regions of the Bering Sea. Only north
of the Alaska Peninsula, in connection with a planned
clam fishery for this region, have adequate estimates
been made. More field data are needed, but there are
large amounts of data directly related to walruses, in
these volumes and elsewhere, that have not yet been
fully analyzed and that should get first attention.
Time and interest of competent people Eire needed to
provide such analysis and synthesis. It might be
prudent to delay temporarily further data collection
afield in order to have resources to view existing
evidence and from this establish needed research goals
that will permit the eventual understanding required
for placing these animals appropriately in the Bering
Sea shelf ecosystem.
Phocid seals (ably reviewed by Lowry and Frost,
Chapter 49, this volume), represented by harbor,
spotted, ribbon, ringed, and bearded seals, are all
in competition for carbon in the pelagic food web
with fur seals, sea lions, cetaceans, and birds, as
well as all other members of the pelagic community.
Available data on foods of phocid seals are inadequate
for all seasons and in all regions except for the north,
where the Eskimo subsistence harvest makes it
possible to examine the stomach contents of seals.
There is little chance at present to relate most of
these animals to their environmental energy demands
because of the lack of relevant information. An
exception is the excellent work presented by
Ashwell-Erickson and Eisner (Chapter 53, this vol-
ume) on studies of the energy cost of the harbor and
spotted seals in the environment; it appears that
these two species alone would consume about
8 X 10^ kg of primary carbon each year. Depending
on where this consumption occurs, this high demand
could represent a substantial proportion of the total
primary production (10 percent of middle-domain
estimate).
Research opportunities in this field are seriously
limited by the lack of logistics to support ice-edge
and inner ice-zone work on the Bering Sea shelf in
fall, winter, and spring seasons, when the activities
of these voracious animals occur.
There are 13 species of cetaceans (Frost and
Lowry, Chapter 50, this volume) which inhabit the
Bering Sea shelf for varying amounts of time each
year. All except the gray whale, which feeds largely
on benthic amphipods, compete for food in the
pelagic food web with fishes, pinnipeds, seabirds, and
people. Eleven species regularly spend the summer
feeding in some part of the Bering Sea, and two
species, white and bowhead whales, winter there.
The effect of the whales on food resources is
largely unknown, since the estimates of population
size, residence time, body weights, consumption
rates, prey composition, energy requirements, Eind
metabolic efficiency are only partially known for any
species. Best known perhaps is the gray whale, which
has a population of approximately 15,000 and which
spends much of the year (180 days) on the Bering
Sea shelf. These whales, weighing about 14,000 kg,
consume benthic amphipods amounting to 7-9 per-
cent of their body weight daily (1,000-1,200 kg).
Amphipods feed on deposited organics, detritus,
bacteria, benthic diatoms, and meiofauna; the propor-
tion of each is not clearly defined. A rough estimate
indicates that 1 kg of amphipod carbon is derived
from 5-10 kg of primary carbon. This population,
weighing 2.1 X 10^ kg (1 X 10^ gC @ 5-percent
wet weight), occupies about 1 X 10'^ m^ (an area
nearly as large as the Bering Sea shelf) and con-
sumes from 6.3 to 16 X 10'' g primary carbon each
season, or about 3-16 gC/m^/yr. If we assume a pri-
mary production rate of 200 gC/m^/yr for the entire
region, then the gray whale consumption is between
1 .5 and 8 percent of the total production, compared
with 1.2-3.4 percent of the total benthos as cal-
culated by Frost and Lowry (Chapter 50, this vol-
ume). Since this is average consumption over most
of the shelf area, local consumption in some regions
could be several times higher.
From the above estimate of food consumption for
the gray whale, it is clear that the cetaceans place a
very heavy demand on the ecosystem of the Bering
Sea shelf. Data for similar estimates of any other
species are not available. Although the cetaceans in
general have been sought by man the world over
since as early as 875 a . d . by the Basques and per-
haps earlier by the Norwegians (Hardy 1967), there
seems to be relatively little known about these, the
largest of earth's living animals. Numbers of most
species are uncertain, their food requirements only
superficially understood, their behavioral patterns
mostly unknown, their energy requirements in doubt,
and considerations of their impact on the ecosystem
mostly neglected. Public attitudes about whales,
as well as many other marine mammals, and the
difficulty encountered in working with such large
animals have effectively placed most whale research
in the category of nature studies. Better effort is
badly needed to understand how these animals
function as individuals, as a community, and within
the ecosystem.
Marine birds
Marine birds have a population level in the Bering
Sea shelf region of approximately 50 million, com-
Environmental risks and research opportunities 1319
prise 14 species with a total mass of 2.4 X 10^ kg,
and consume one million mt of food a year (Hunt
et al., Chapter 38, this volume). Of these the Slender-
billed Shearwater is most abundant in numbers (13.5
X 10^) as well as in biomass (9.4 X 10*^ kg); it
consumes mainly euphausiids and amphipods. Second
in abundance (4.9 X 10* ) and biomass (5.3 X 10* kg)
is the Thick-billed Murre, which feeds heavily on
pollock (30 percent) and other fish (30 percent);
third is the Common Murre with an abundance of
4.2 X 10* and a biomass of 4 X 10* kg, which feeds
mainly on pollock (35 percent) and other fish (45
percent). The importance of birds as consumers of
the energy budget of the Bering Sea shelf is unques-
tioned, as the data for the two murre species in
Tables 71-3 and 71-4 demonstrate.
The outstanding efforts of the biological oceanog-
raphers working on birds, well represented by the
chapters in Section VI of this volume, have produced
data that can now readily be used by other oceanog-
raphers to put together the ecosystem puzzle of the
eastern Bering Sea. Clearly it is now time for the
"bird people" to be joined by other ecosystem-
oriented scientists so that each can profit from inter-
disciplinary interaction. Only in this way have
scientists learned much about oceanography or other
environmental science. The rapid progress that has
been made recently should be greatly enhanced in
the future by examining those factors in the environ-
ment (at all seasons) which influence the abundance,
location, and food-selection habits of birds and
applying the information appropriately to a holistic
view of the Bering Sea ecosystem.
Benthos
The last, but not the least important, category to
be discussed in these few summary statements on re-
search opportunities is the very large and often
neglected realm of benthic biology. The impressive
group of studies in Section XII covers fairly well
the reconnaissance level of information needed on
infaunal and epifaunal distributions and relative abun-
dances, except perhaps for some regions such as
Norton Sound and the Navarin Basin. Moreover, the
feeding interactions of benthic biota and other biotic
communities and within the community itself have
been quite well established (Feder and Jewett, Chap-
ter 69, this volume). Little has yet been done to
establish the flow of energy quantitatively through
the benthic community and those other biotic
communities depending upon it.
On the shelf, at least from the 100-m contour
shoreward, it appears that of all biotic components,
the benthic community is by far the greatest user of
primary production. Its requirements exceed the
presently estimated available primary carbon pro-
duced. Despite this heavy consumption, the flow of
carbon in this community is poorly defined, as are
the environmental factors which influence its utiliza-
tion by the many members of the community.
The function of this community in the ecosystem is
probably the least understood of all communities,
except perhaps that of marine mammals. This situa-
tion is urgently in need of resolution as we face the
ever-increasing stresses of human activities (or in-
activities) on the environment.
Advances in benthic biology will now most likely
result from the work of fully cooperating members
of an interdisciplinary team of scientists who attempt
to unravel the important concepts of energy transfer
through the biota. Much needed are rate studies,
i. e., growth, feeding, and metabolism and how these
are influenced by stresses either natural or anthropo-
genic. The disciplines of marine microbiology, phys-
iology, and biochemistry, often neglected by the
more descriptive approaches, can be incorporated
here. Probably of equal importance are physical
and chemical studies of dispersion, sorption, and
equilibrium, which must play a significant role in
what happens and where and how fast it happens
in sediment processes and interactions between
sediment and the water column. In benthic biology
we appear to be dealing with a "black box" which is
fairly well described outwardly but must now be
opened and examined.
A SUMMARY NOTE
In nearly all the studies reported in these two
volumes, there is a serious gap in fall and winter data
resulting from a lack of effective logistic support
for scientific work in ice-covered waters or under con-
ditions conducive to formation of ice on floating
platforms. This gap exists despite the fact that the
Bering Sea shelf is unsurpassed by any region of
the world as a biological and possible energy re-
source for the supply of human needs. No other
region offers its equivalent in amounts and varieties
of biota that are now used or potentially useful,
nor does any offer greater promise for the pro-
duction of energy. Both are needed and full exploita-
tion of both is planned.
The research efforts reported here are probably of
as high quality as the present state of the art in
oceanography will permit. Great progress has been
made in understanding the Bering Sea ecosystem,
which has developed through centuries to provide the
bountiful harvest of this region. Far greater under-
standing is needed before it will be possible to predict
1320 Summary and perspectives
events which influence the functioning of this eco-
system and its various components. To accomplish
this ultimate goal, it is essential that a firm base of
knowledge be established for all seasons of the year,
including those when this shelf is mostly covered
with ice.
Studies of this type require the acquisition of an
oceanographic research platform that can function
in ice and under difficult weather conditions and at
the same time accommodate the necessary scientific
party and tools to carry out the needed work effi-
ciently. The cost of such equipment is high, probably
$30 million for acquisition and about $3 million
annually for operating costs. This does not seem so
high, however, when one considers that the harvest
of all countries' present commercial fisheries exceeds
$2.5 bUlion annually, with the U.S. portion increasing
on a self-determined schedule, because all this region
lies within the 200-mile U.S. jurisdictional limit.
This huge amount of commerce excludes any valua-
tion of nonharvested biological or mineral resources.
It would appear that a capital investment of
1 percent and an operational budget of 0.1 percent
of the annual yield is a small price to pay to help
understand and protect the uniquely bountiful region
of the eastern Bering Sea and also the neighboring
areas to the north in the Chukchi and Beaufort seas.
ACKNOWLEDGMENTS
The authors of this chapter— the editors of the two
volumes— wish to thank the 130 authors and 12
associate editors who contributed so vigorously to
producing the material in this first Bering Sea shelf
book. In the preparation of this chapter we have
drawn from all parts of the book, but also from the
workshop held in Anchorage on 13-15 November of
1979 in connection with a symposium in which many
of the chapters appearing here were presented. We
wish to acknowledge the chairmen and participants
in these workshops for their mature view of scientific
needs in the Bering Sea and for their willingness to
allow us to extract from their views so freely here.
The chairmen were: physical oceanography, Eddy
C. Carmack; fisheries oceanography, Ole A. Mathisen;
geology and ice, Peter J. Fischer; chemical oceanog-
raphy, Herbert E. Bruce; plankton ecology, David
W. Menzel; marine mammals, Robert Farentinos;
marine birds, George L. Hunt, Jr.; benthic biology,
Paul R. Becker; and ice-edge ecosystems, David
Nyquist.
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1981 Microbial degradation of hydrocar-
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Berne, S., M. Marchand, and L. d'Ozouville
1980 Pollution of sea water and marine
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Boehm, P. D., J. Barak, D. Fiest, and A. Elskus
1980 The analytical chemistry of Mytilus
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Boehm, P. D., and D. Fiest
1981a Subsurface water column transport
and weathering of petroleum hydro-
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in the Bay of Campeche and their
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from the September 1979 Research-
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1981b Aspects of the transport of petroleum
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during the Ixtoc I blowout in the
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Brooks, J. M., D. A. Wiesenburg, R. A. Burke,
M. C. Kennicutt, and B. B. Bernard
1981 Gaseous and volatile hydrocarbons in
the Gulf of Mexico following the
Ixtoc I blowout. In: Proceedings of
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Washington, D.C.
Fiest, D. L., and P. D. Boehm
1981 Subsurface distribution of petroleum
from an offshore well blowout— The
Ixtoc I blowout. Bay of Campeche.
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D.C.
Cabioch, L.
1980
Calder, J. A.
1979
Pollution of subtidal sediments and
disturbance of benthic animal com-
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Weathering effects on the chemical
composition of the Amoco Cadiz
oil. Presented at the annual meeting
of the A A AS, Houston, Texas. Cited
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Hardy, Sir Alister
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1976 Assessment of the arctic marine envi-
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Hood, D. W., and E. J. Kelley, editors
1974 Oceanography of the Bering Sea.
Inst. Mar. Sci., Occ. Pub. No. 2,
Univ. of Alaska, Fairbanks.
Calder, J. A., and P. D. Boehm
The chemistry of Amoco Cadiz
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Horowdtz, A., and B. J. Presley
1977 Trace metal concentrations and par-
titioning in zooplankton, neuston
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outer continental shelf. Archives of
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Calder, J. A., J. Lake, and J. Laseter
1978 Chemical composition of selected
environmental and petroleum samples
from the Amoco Cadiz oil spill.
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preliminary scientific report, W. N.
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Iverson, R., and J. Goering
1979 Primary production and phytoplank-
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Jordan, R. E., and J. R. Payne
1980 Fate and weathering of petroleum
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Ann Arbor Science Publishers, Ann
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1980 Metal levels in sediment and ben-
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Kineman, J.
1980
NOAA acute phase experiments on
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Boulder, Colo.
1322 Summary and perspectives
Linden, O., R. Elmgren, L. Westin, and J. Kineman
1980 Scientific summary and general dis-
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Boulder, Colo.
McGlothlin , R. E., and H. Krause
1980 Water base drilling fluids. Proc.
Research on environmental fate and
effects of drilling fluids and cuttings.
API, APOAetal. 1:30-7.
McMordie, W. C, Jr.
1980 Oil base drilling fluids. Proc. Research
on environmental fate and effects
of drilling fluids and cuttings. API,
APOAetal. 1:38-42.
Nelson, T. A.
1981
Mineralogy of suspended and bottom
sediments in the vicinity of the
Ixtoc I blowout, September, 1979.
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D.C.
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1981 Photochemical oxidation of Ixtoc I
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D.C.
Payne, J. R. N. W. Flynn, P. J. Mankiewicz, and
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1981 Surface evaporation/dissolution par-
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Payne, J. R., G. S. Smith, J. L. Lambech, and P. J.
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1980 Chemical weathering of petroleum
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Perricone, C.
1980 Major drilling fluid additives— 1979.
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fate and effects of drilling fluids and
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Ross, S. L., C. W. Ross, F. Lepine, and E. K. Langtry
1981 Ixtoc I oil blowout. In: Proceedings
of a symposium on preliminary
results from the September 1979
Researcher/Pierce Ixtoc I cruise.
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Tomberg, L. D., E. D. Thielk, R. E. Nakatani, R. C.
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1980 Toxicity of drilling fluids to marine
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cuttings. API, APOAetal. 2:997-1016.
Index: Volumes I and II
aalge, Uria, see Common Murre.
Acartia clausi, 951
Acartia longiremis, 770, 940, 947,
950, 951, 952, 953
Acartia spp., 942, 984
acceptable biological catch, fish, 1033
acervata, Leptasterias polaris, 1134,
1136, 1137, 1138, 1141, 1146,
1147, 1149-51
Achnanthes spp., 778, 936
Acinetobacter, 904
acipenserinus, Agonus, 483
Acmaea spp., 1120
acoustic anomalies, 420
acuminata, Calidris, see Sharp-tailed
Sandpiper
acuta. Anas, see Pintail
acutorostrata, Balaenoptera, see minke
whale
Adak Island, 17, 18; crab fisheries,
1041
advection, Norton Sound, 87-8, 90
aeglefinus, Melanogrammus, see had-
dock
aequalis, Mediaster, 1109
aequispina, Lithodes, see golden king
crab
aerodynamic drag, 189, 202, 207, 210
Aethia cristatella, see Crested Auklet
Aethia pusilla, see Least Auklet
Aethia pygmaea, see Whiskered Auklet
Afognak Island, 1231, 1233
Agonus acipenserinus, 483
Agonidae, larvae, 483-4
Air -sea interaction, 10
Akun Island, algae, 1116-22; barnacles,
1121-2; herbivores, 1119-21 ; mollusks,
1110-15; species density, 1111-14;
species importance, 1114-15
alanine, 373
Alaria spp., 1116-18, 1120, 1123
Alaska Department of Fish and Game,
808, 844, 1041
Alaska plaice, see flatfish; plaice
Alaska surf clam, 1205, 1213, 1236
Alaskan Stream, 359, 363, 368, 565
alata, Rhizosolenia, 938, 941-2
alba, Calidris, see Sanderling
alba, Cylichna, 310
Albatross, 694
albatrus, Diomedea, 694
albifrons, Anser, see White-fronted
Goose
alcids, 665-74, 690; distribution, 704-
12; reproduction, 679
Alectridium aurantiacum , 485
aleutensis, Lyconectes, 486
Aleutian Canada Goose, 748
Aleutian Islands, albatross, 694; alcids,
710; Aleutian Canada Goose, 748-9;
arctic flounder, 919; auklets, 669-71,
706; cormorants, 654; eiders, 748-9,
Emperor Goose, 747; fulmars, 650,
694; harbor seals, 814, 873;ichthyo-
plankton distribution, 475-90; kitti-
wakes, 662; northern fur seals, 851;
northern sea lions, 861 ; puffins,
672-4, 708; Sanderling, 732; sea
otters, 837; Sharp-tailed Sandpiper,
733; starry flounder, 919; storm-
petrels, 698; terns, 663
Aleutian Low, 15, 25
Aleutian passes, 33,63
Aleutian range, surfbirds, 731
Aleutian Tern, 664-5, 704
aleutica, Littorina, 1119, 1124
aleutica. Sterna, see Aleutian Tern
aleuticus, Ptychoramphus, see Cassin's
Auklet
algae, distribution, 1116-21, 1123,
1125; in harbor seal diet, 815; in red
king crab diet; in sea ice, 939
alkanes, 392, 399, 402, 404, 433,
435
alkenes, 402, 433, 435
Alle alle, see dovekies
Alopex lagopus, see arctic fox
alpina, Calidris, see Dunlin
aluminosilicate, 329, 332
aluminum, 314-16, 321, 324, 329-32
Amak Island, algae, 1116-21; barnacles,
1121-2; crabs, 450; herbivores, 1119-
21; mollusks, 1110-15; northern fur
seals, 852; sea otters, 840, 843;
species density, 1111-14; species
importance, 1115-6
Amchitka Island, 814, 844, 1116
Amchitka Pass, auklets, 706
Amee Island, terns, 664
American Golden Plover, 721-4, 727, 733,
736
amino acids, 372-4
Ammodyies hexapterus, see sand lance
Ammodytidae, larvae, 486
ammonia, concentration, 768-9; under
ice, 775-6, 778; utilization, 351-52
ammonium, concentration, 980-87;
oxidation, 987-8; in seawater, 979-
86; source, 981
Amoco Cadiz oil spill, 1305-08, 1310
1323
Ampelisca spp., in gray whale diet,
829
amphidrome, 117, 119, 122
amphipods, abundance, 1073; in auklet
diet, 638-40, 644, 706; in bow-
head whale diet, 828; in cormorant
diet, 641; diet, 1318; distribution,
947, 949-51, distribution related to
sediment size, 310-11; feeding at sea
ice, 769; hydrocarbons in, 384; in
gray whale diet, 819, 829; in hump-
back whale diet, 828; in kittiwake
diet, 641, 644; in mammal diet, 770;
in murre diet, 636-7, 641, 644; in
Pacific cod diet, 1238; in Pacific
herring diet, 516; in plaice diet,
1239; in puffin diet, 641, 644; in red
king crab diet, 1232; in ribbon seal
diet, 815; in ringed seal diet, 816,
819; in sea ice, 774; in seabird diet,
770, 799; in shearwater diet, 631,
1238; in spotted seal diet, 815; in
walleye pollock diet, 541. 1238; in
yellowfin sole diet, 561, 1240; see
also specific amphipods
Amphiuridae, 1233
Amundsen Gulf, beluga whale at, 792
amurensis, Asterias, see sea star
amygdalea, Yoldia, 1159, 1165-7, 1169-
70, 1172-4, 1176-7, 1179-80, 1182
Anadyr Bay, see Gulf of Anadyr
Anadyr River, 460
Anadyr Strait, 1085
Anarhichadidae, larvae, 485
Anarhichas orientalis, 485
Anas acuta, see Pintail
Ancient Murrelet, distribution, 710-11
angulatus, Chionoecetes, see Tanner
crab
angulosum, Buccinum, 1220, 1224
annelid, 907, 1073, 1137
Anonyx spp., 829, 1238
Anoplopoma fimbria, see sablefish
Anoplopomatidae, larvae, 481-2
Anser albifrons, see White-fronted
Goose
Anser c. caerulescens, see Lesser Snow
Goose
Antarctophthirius callorhini, see seal
lice
antiqua, Neptunea, 1223, 1224
antiquus, Synthliboramphus, see An-
cient Murrelet
Aphriza virgata, see Surf bird
Aptocyclus ventricosus, 484
1324 Index: arabinose
arabinose, 374-5
arcta, Spongomorpha, 1116, 1118
Arctic Basin, evolution, 298
arctic char, 774
arctic cod, 774; abundance, 528;
in beluga whale diet, 830; in Black-
legged Kittiwake diet, 634-5; in Dall
porpoise diet, 831; in fin whale diet,
827 ; in humpback whale diet, 828 ; in
killer whale diet, 830; in minke
whale diet, 828; in murre diet, 636-7;
in pinniped diet, 819; in ribbon seal
diet, 815-6; in ringed seal diet, 816;
in seabird diet, 642, 799, 802; in sei
whale diet, 827; in spotted seal diet,
815
arctic flounder, 919
arctic fox, 677, 788-9, 858
arctic shanny, 485
Arctic Tern, 663-5, 704
arctica, Fratercula, see Common Puffin
arctica, Hiatella, 1084
Arctogadus glacialis, see polar cod
Arenaria interpres, see Ruddy Turn-
stone
Arenaria melanocephala, see Black
Turnstone
argentatus vegae, Larus, see Herring
Gull
arginine, 373-4
Argis spp., 817
Argo Merchant, oil spill, 237
aromatic compounds, 392-4, 400, 404,
1306
arrow worms, hydrocarbons in, 384
arrowtooth flounder, 487, 542, 960,
1026, 1028, 1232, 1238-40
Artediellus pacificus, 483
Arthropoda, 1133-7
Ascidia nigra, 907
ascidians, 829. 1236
aspartic acid, 373-4
aspera, Limanda, see yellowfin sole
Aspidophoroides spp., 483
Asterias spp., 1133-35, 1137, 1141-2,
1144, 1146-51, 1233, 1236
Asterias amurensis, see sea star
Asterias rathbuni, 1134
Asterophila japonica, 1150
Asterotheca infraspinata, 483
Atheresthes spp., see arrowtooth
flounder
Atka mackerel, 480, 815, 827-9, 831
Atlantic cod, 1007-8
Atlantic halibut, 496
Atlantic herring, 510
Atlantic mackerel, 874
Atlantic surf clam, 1205, 1213
atmospheric pressure, related to trans-
port, 90, 105-6, 109
Atylus spp., in gray whale diet, 829
auklet, 638, 649, 669, 706-08; see also
specific auklets
aurantiacum, Alectridium, 485
auritus, Phalacrocorax, see Double -
crested Cormorant
Axinopsida serricata, 1173
Ay thy a marila, see Greater Scaup
B
Baby Islands, 671, 673
Babylonia japonica, 1224
bacillary dysentery, 903
bacteria, 905-08
Bacteriosira fragilis, 936
bacteriovores, 905, 907
Baffin Island, 1080
Baird Bank, 449
bairdii, Berardius, 825
bairdii, Calidris, 733
Baird's beaked whale, 825, 830
Baird 's Sandpiper, 733
Balaena mysticetus, 623, 788, 791-4,
807-08, 828, 831
Balaenoptera acutorostrata, 825, 828,
831
Balaenoptera borealis, 827
Balaenoptera musculus, 827
Balaenoptera physalus, 825-7, 831
Balanus spp., 1118, 1121-3, 1231-2,
1234-6
baleen whales, 825-6, 954
balthica, Macoma, 726
barbatus, Erignathus, see bearded seal
Barclay Sound, 553
Barents Sea, 633, 636, 637, 642
barnacles, 1118, 1121-3, 1224, 1231-2,
1234, 1236
baroclinic coastal flow, 87
Bar-tailed Godwit, 721, 723, 726,
728,732
bartoni, Aspidophoroides, 483
basket star, 1134, 1136, 1138, 1143,
1151, 1232
Bathylagidae, 476-7, 831
Bathylagus spp., 476
Bathy master signatus, 484
Bathymasteridae, 484
Bay of Anadyr, see Gulf of Anadyr
beach goose, 745, 747
beaked whales, see Baird's beaked
whale, Cuvier's beaked whale,
Stejneger's beaked whale
bearded seal, calving, 789, 793; diet,
813, 816-17, 1235, 1242; food web,
818; habitat, 759, 788, 789, 792
793, 808, 816-17; heavy metal con-
tent, 342; hydrocarbons, 384
Bechevin Bay, 843, 844
bedform migration, 255, 258
beluga whale, 623, 759, 774, 788,
791-4, 808, 830, 832; see also
white whale
benthic community, 400, 615, 622,
779, 1069, 1091, 1101, 1319;
abundance, 1073, 1079, 1080; clus-
tering, 1077, 1079-81, 1084-6,
1094-7; distribution, 1073, 1076-7,
1079-81, 1083-5, 1087, 1220, 1230;
effect of ice, 759, 799; environmen-
tal factors, 769, 1077, 1079, 1086,
1087, 1100; food web, 614, 942-3,
1155, 1317; nutrients, 1073; preda-
tors, 342, 452, 618, 819, 832, 859-
61, 959, 1069, 1081-4, 1100; rela-
tion to sediment size, 310-11; under
sea ice, 774; variation, 1079, 1086-7
benthic sharks, 829
benzene, 1306
benzo(E)pyrene, 404
benzoperylene, 404
Berardius bairdii, 825, 830
Bering, Vitus, 807
Bering flounder, 487
Bering poacher, 483
Bering Slope Current, 8, 56, 69, 72,
782, 1109
Beringius beringii,1221, 1223
bernicla nigricans, Branta, 743-5, 747
Berryteuthis magister, see squid
Big Diomede Island, 675
bigeye lanternfish, 477
bilineata, Lepidopsetta, see rock sole
biochemical cycles, 906
bioenergetics, 871
biomass, 611-14, 617; bacterial, 905-06,
912; benthic, 1080; bivalve, 1173,
1175; epifaunal, 1133, 1151;equiH-
brium, 614-17; phytoplankton,
984; related to species importance,
1115-16; zooplankton, 950-4
bioturbation, 1277-80, 1286-7
bivalves, 829, 1070, 1157, 1224, 1232,
1 246-9 ; see also clams
Black-bellied Plover, 7 21, 727
Black Brant, 743-5, 747
blackfin sculpin, 483
Black-footed Albatross, 694
Black Guillemot, 650, 668, 710, 800-
01,803
Black-headed Gull, 700
Black-legged Kittiwake, 656-63, 676,
677; colonies, 652, 653, 657; diet,
632-5, 640-1; distribution, 656,
690, 694, 701-02, 712, 800; habitat,
657; hydrocarbons, 384; phenology,
657-9; reproduction, 657-60
Black Scoter, 750
Black Sea, 435
Black Turnstone, 721, 726, 730, 735
blenny, 830
bloom, 763-4, 767, 770, 771, 984,
see also phytoplankton bloom
blue king crab, 1039-40, 1045-6,
1050, 1133, 1145-6
blue whale, 827
bluff, 634, 636, 653, 660, 662, 666
Bogoslof Island, 635, 662, 703, 852
Index: carbon dioxide 1325
bolini, Ulca, 542
Boltenia, 1233
Bonaparte's Gull, 700
borchgrevinki, Trematomus, 11 A
borealis, Balaenoptera, see sei whale
borealis, Icelinus, 483
borealis, Neptunea, 1219
borealis, Pandalus, 1231-2
Boreogadus saida, see arctic cod
Bowers Ridge, 486
bowhead whale, 623, 788, 791-4,
807-08, 825, 828, 831
Brachyramphus spp., 650, 710-11
brandtii, Schizoplax, 1119-20
Brandt's Cormorant, 650
Branta spp., 743-8
brevirostris, Brachyramphus, 710
brevirostris, Rissa, 635, 640-4
Bristle-thighed Curlew, 7 28-9
Bristol Bay, auklets, 669; beluga whale,
792, 793, 830; benthic fauna,
1097; Black-bellied Plover, 727;
Black Brant, 744; Black Scoter,
750; Black Turnstone, 730; Cackling
Canada Goose, 746; circulation,
56, 306; Common Snipe, 731;
copepods, 954; cormorants, 652,
654; description, 182-6, 216, 426,
740-3; dissolved hydrocarbons,
426-7; Emperor Goose, 744; fast ice,
182; fulmars, 694; Glaucous Gulls,
655; Greater Yellowlegs, 729; hali-
but, 497; harbor seal, 814-15, 873;
hydrocarbons, 431; ice formation,
216, 604, 786-7; ichthyoplankton,
475-90; King Eider, 744, 749; Pacif-
ic herring, 476, 512-13, 516, 519;
pack ice, 182; Pectoral Sandpiper,
733; Pintail, 744; Red Phalarope,
730; river plumes, 44; Rock Sand-
piper, 725; rock sole, 919; runoff,
600; salinity, 602; salmon, 578, 581-
91, 959; Sanderling, 7 32; sandpipers,
732-3; sea otters, 839-45; sea-
surface temperature, 24, 136;
Short-billed Dowitcher, 731; spotted
seal, 789, 815; Steller's Eider, 749;
Surfbird, 731; tides, 117, 122, 123;
walrus, 789, 817, 1081; Wandering
Tattlers, 7 29; waterfowl, 739;
Whimbrel, 728; yellowfin sole, 556,
561-3, 603, 605; zooplankton,
954-5
Bristol Bay River, current, 456
brittle star, 1231, 1232
Brooks Range, 294, 297, 299, 731
Buccinum spp., 817, 1220-1, 1224,
1232
Buckland, 727
Buff-breasted Sandpiper, 734
Buldir Island, 635, 662, 671, 703,
748
Bulk Biomass Model, 614-15
bungii, Eucalanus bungii, 770, 947,
950-3, 955
buoys, drogued, 5, 8, 56, 65
Bureau of Commercial Fisheries, 1030
butanes, distribution, 431, see also
iso-butane, n-butane
butter sole, 1029
Buzzards Bay, Massachusetts, oil spill,
224
cachalot, see sperm whale
Cackling Canada Goose, 745-7
cadalene, 402
cadmium, 341-5
caeca, Nephthys, 310
caerulescens, Anser caerulescens, 745,
747
calanoids, 384, 516, 541, 638
Calanus cristatus, 639, 770, 826-
7,940, 947, 950, 952-3
Calanus glacialis, 770, 947, 951
Calanus marshallae, 639, 770, 951,
953
Calanus plumchrus, 639, 770, 826,
940, 947, 950, 952-3, 955, 1317
Calanus spp., 399, 402, 516, 638, 827
calcarea, Macoma, 1159, 1167, 1173-
4, 1176-83, 1236
calcium, 324, 330-1
Calidris spp., 721, 723-6, 731-6
California headlight fish, 477
California sea lion, 863, 883
californianus, Mytilus, 907
californiense, Clinocardium, 1232
Callinectes sapidus, 1037
callorhini, Antarctophthirius, 903
Callorhinus ursinus, see northern fur
seal
camtschatica, Paralithodes, see red king
crab
Canada, fisheries, 1016-17, 1030; fishery
agreements, 495, 1031
canadensis minima, Branta, 745-7
canadensis leucopareia, Branta, 748
canadensis taverneri, Branta, 745-6
Canadian Beaufort Sea Project, 223
canagica, Philacte, 745, 747
Cancer magister, 1038
canus, Larus, 650, 654, 700-01
canutus, Calidris, 721-4, 731-2
Cape Avinof, 180, 182, 749
Cape Cheerful, 852
Cape Cod Canal, 224
Cape Constantine, 512
Cape Corwin, 182
Cape Darby, 85, 87-90, 92, 178, 677
Cape Denbigh, 178, 677
Cape Douglas, 514
Cape Espenberg, 294
Cape Etolin, 181
Cape Krusenstern, 294
Cape Leontovich, 839-40, 844
Cape Lisburne, geology, 294; guillemot,
668; puffin, 673; Sharp-tailed Sand-
piper, 733; transports, 97-104, 109;
water level, 106, 108
CapeMendenhall, 182
Cape Mohican, 181
Cape Mordvinof, 840, 844
Cape Navarin, 55, 461, 516, 578,
598, 602-03, 606
Cape Newenham, 43, 65, 66; amphi-
drome, 117, 126; Bristle-thighed
Curlew, 729; cormorant, 652, 678-9;
eider, 748, 749; Emperor Goose,
747; fast ice, 182; Glaucous Gull,
701; Glaucous-winged Gull, 701,
guillemot, 678-9; Harlequin Duck,
749; kittiwake, 676; methane source,
427, 429-30; murre, 705; Pacific
herring, 512; Pintail, 748; Red
Phalarope, 730; seabird population,
675-7; waterfowl, 745; Whimbrel,
729
Cape Nome, 178, 216
Cape Olyutorsky, 362, 606
Cape Peirce, 649, 652-4, 656-7, 665-6,
674-5,748,750
Cape Prince of Wales, 104, 186, 727,
730, 733, 748, 790
Cape Romanzof, 179, 180, 513, 750
Cape Sarichef, 1041
Cape Schmidt, 105
Cape Serdtse-Kamen, 105, 109
Cape Thompson, 232, 294, 632, 634,
636-7, 642, 649, 655, 657, 659, 672
Cape Vancouver, 677
capelin, abundance, 476, 614; distribu-
tion, 476, 770; in jaeger diet, 700;
in kittiwake diet, 632; larvae, 476;
in murre diet, 637; in Pacific cod
diet, 1238; in Pacific herring diet,
516; in pinniped diet, 819; in por-
poise diet, 831; pristane, 384;
in red king crab diet, 1233; in sea-
bird diet, 661, 675, 677, 802; in
seal diet, 815-16, 857-8, 861, 891;
in shearwater diet, 631; in whale
diet, 827-8, 830-1; in yellowfin sole
diet, 560
carbohydrates, 374-5
carbon, 324, 332, 360, 778; analysis,
390; budget, 347-9, 356; cycle, 348,
354-5, 911, 1312; detrital organic,
371-2; fixation, 770; at ice edge,
759; isotopic values, 401, 413, 418;
microalgal, 401; to nitrogen ratio,
905, 907-08, 910; organic, 360-7,
392-3, 434, 909-10, 1174, 1230,
1312-13; production, 773, 1316;
in sea ice, 769
carbon dioxide, 911; cycle, 348-9; deri-
vation, 347; exchange, 354-6; flux,
347, 353, 355; from sediment, 256,
413, 418-22, 437; system, 909;
transfer, 355-6; variations, 352-4
1326 Index: Carex
Carex spp., 743, 746, 747
Cariaco Trench, 400
cariosus, Balanus, 1118, 1121, 1123
carneipes, Puffinus, 696
carrion, 631, 701
caryi, Gorgonocephalus, 1134-5, 1138,
1143,1151,1232
Cassin's Auklet, 638, 710-11
catodon, Physeter, 623, 825, 829, 832
cavirostris, Ziphius, 825, 830, 831
Centropages abdominalis, 951
cephalopods, in auklet diet, 641, 644;
in Dall porpoise diet, 831; in Fork-
tailed Storm -Petrel diet, 644, 698;
in fulmar diet, 630-1, 641, 644,
676-7; in kittiwake diet, 641, 644;
in murre diet, 636-7, 641, 644;
in puffin diet, 640-1, 708; in
ribbon seal diet, 815; in sculpin
diet, 1239; in shearwater diet,
631, 644; in whale diet, 826, 829-31
Cepphus spp., 650, 668-9, 676, 710,
800-01,803
Cerorhinca monocerata, 650, 710-11
cetaceans, see specific whale or por-
poise
Chaetoceros spp., 936-8, 940,
941,980
chaetognaths, 384, 950-1
Chagulak Island, 650, 676, 694
chalcogramma, Theragra, see walleye
pollock
Charadrii, see shorebirds
Charadrius semipalmatus, 721, 727
Chauliodus macouni. All
Chelysoma orientale, 1236
Chiniak Bay, 664-5
Chinook salmon, 575-80, 582, 583,
585-7, 591
Chionoecetes spp., see Tanner crab
Chirikov Basin, 279, 411, 418-20,
1081-2, 1084
Chirolophis polyactocephalus, 485, 637
Chironomidae, 726
Chlamys spp., 1232
chlorite, 311-13
chlorophyll, 764, 769, 778-9; concen-
trations, 41, 360; distribution, 362-7,
775-6, 976, 984-6; hydrocarbon
production, 434; at ice surface, 767;
measurements, 360, 773; profile,
362 ; relation to carbon dioxide, 351 ;
Unimak Pass, 986
Chordata, 1137
chrysene, 404
Chthamalus dalli, 1121
Chukchi Sea, 19, 54, 313, 335, 1240
Chukotsk Peninsula, 293-4, 296, 731,
747-8, 785,791
Chukotsk Range, 293
chum salmon, 450, 575-87, 591, 608,
1238
ciliates, 774
ciliatum, Clinocardium, 1097, 1151,
1159, 1168-71, 1173, 1231, 1233
circulation, atmospheric, 7-8, 15, 19-20,
23-7, 133; water, 53, 56-8, 63-8,
305-06, 323, 334, 428, 430, 463,
934-6, 1156
cirrhata, Lunda, 639-41, 644, 673,
708-09, 712
cirripeds, 516
Cistenides sp., 1233, 1236
Cladocera, 516, 951
clam, age determination, 1177-83; in
bowhead whale diet, 828; diet,
1238; distribution, 1157; fishery,
1131, 1205, 1209, 1213; in flatfish
diet, 1155; growth, 1179; in king
crab diet, 1155, 1175-6, 1183, 1233;
in Pacific Cod diet, 1238; in plaice
diet, 1239; in sea star diet, 1236; in
seal diet, 816-17; in Tanner crab diet,
1155, 1175-6, 1183, 1235; in walrus
diet, 817, 818; in yellowfin sole diet,
560-1
Clangula hyemalis, 745, 749-50, 800
Clarence Rhode Range, 747, 748
clausa, Natica, 1236
clay, 307, 309, 311-14
Clinocardium calif orniense, 1232
Clinocardium ciliatum, 1097, 1151,
1159, 1168-71, 1173, 1231, 1233
Clinocardium spp., 817, 1084, 1234,
1238
Clinopegma magna, 1220
closterium, Nitzschia, 118
clouds, 18, 20-22, 27-8, 457
Clupea harengus pallasi, 449, 451-2,
473, 475-6, 509-22, 831, 1020, 1023
Clupeidae, see specific herring
Cnidaria, 1137
coarctatus alutaceus, Hyas, 1232
coastal flooding, 251, 258
cockles, 1155, 1234, 1236, 1238-9
cod, 449-50, 477-80, 828, 831; see also
Pacific cod
coho salmon, 575-80, 582-3, 585-8,
590-1, 608
Cold Bay, 843, 844
coli, Escherichia, 905-7
Collisella spp., 1119, 1120, 1123
columba, Cepphus, 668-9, 676, 710
columbianus, Cygnus, 745-6
Colville Delta, 288,728
Colville GeosyncHne, 294, 297, 298
Colville River, 749
Commander Islands, see Komandorsky
Islands
commercial fisheries, see fisheries
Common Eider, 748-9
Common Murre, 665-7, 676, 677
diet, 635-6, 640-1, 644, 1319
distribution, 694, 704-06, 1319
hydrocarbons, 384
Common Puffin, 672
Common Snipe, 731
Common Tern, 704
Constantinea, 1124
consumption rates, pinnipeds, 870
Convention on the Continental Shelf,
1040, 1046
Convention for the Preservation and
Protection of Fur Seals, 847
convergence fronts, 689
Cook Inlet, 431, 437, 441, 721, 1231,
1235, 1238, 1239
cookii, Pterodroma, 698
Cook's Petrel, 698
copepods, in auklet diet, 641, 676,
706, 832; consumption of bacteria,
905, 907; distribution, 947-9, 984,
1230; ingesting phytoplankton, 941,
942; feeding on ice-edge bloom,
770; in kittiwake diet, 641 ; in minke
whale diet, 828, 832; in Pacific
herring diet, 510, 515-16; in salmon
diet, 907; in seabird diet, 799;
in sea ice, 774; in walleye pollock
diet, 541, 832, 954, 1238; in whale
diet, 826-8, 832
copper, 314-16, 324, 332, 333, 339-42,
343-5
Copper River Delta, 721, 731, 734
coprophagy, 908
coral, 907
cormorants, 652-4, 656, 676, 700
corniculata, Fratercula, 639-41, 644,
672, 708, 712
coronene, 404
Coryphaenoides pectoralis, 480
cotidal charts, 117, 127
cottids, 482-3, 614, 632, 636, 815,
1016
crab, 450, 502-03, 632, 700, 817,
829, 1238; fisheries, 450, 1039-47,
1053-4, 1058-60; see also specific
crabs
Crangon spp., 817, 1238-9
craterodmeta, Diamphiodia, 1231-2,
1235, 1240
crebricostata, Cyclocardia, 1084, 1159,
1169, 1171, 1173, 1236
crenatus, Balanus, 1231, 1234
Crested Auklet, 638-41, 643-4, 670-1,
674, 694, 706-08, 712
cristata, Cystophora, 788
cristatella, Aethia, 638-41, 643-4,
670-1, 674, 694, 706-08, 712
cristatus, Calanus, 639, 770, 826-7,
940, 947, 950, 952-3
Cristispira spp., 909
crotonensis, Fragilaria, 7 78
crowberries, 746
crustaceans, in alcid diet, 710; in cor-
morant diet, 632; in Dall porpoise
diet, 831; effect of oil spill, 1306,
1308; in murre diet, 637; in Pacific
cod diet, 1238; in plaice diet, 1239;
in red king crab diet, 1232-4; in seal
diet, 814-16; in snail diet, 1224; in
storm-petrel diet, 651; in Tanner
crab diet, 1235; in walrus diet, 817;
in whale diet, 826, 830; see also specific
crustaceans
Index: fast ice 1327
currents, 84-90, 172, 180, 186, 215,
218,456, 1267, 1319
Cuvier's beaked whale, 825, 830, 831
cycloalkanes, 402
Cyclocardia spp., 1084, 1151, 1159,
1171, 1173, 1236, 1238
Cyclorrhynchus psittacula, 638-41, 643-
4, 669-70, 706-08, 712, 801
Cygnus columbianus, 745-6
Cylichna alba, 310
cylindricus, Nitzschia, 778, 936
Cylindropyxis temulens, 940
Cystophora cristata, 788
D
Ball porpoise, 808, 825,830-1, 861-2
dalli, Chthamalus, 1121
dalli, Crangon, 1238-9
dalli, Phocoenoides, 808, 825, 830-1,
861-2
DAPP, 782
daubed shanny, 485
decapods, 641, 950
decorated warbonnet, 485
De Long Mountains, 294, 297, 299
Delphinapterus leucas, 623, 759, 774,
788, 791-4, 808, 825, 830-1
denitrification potential, 904
density stratification, 84, 86
Denticula seminae, 980
dentigera, Laminaria, 1124
depression area, 254-5, 257-8
Detonula spp., 936
detrital organic carbon, 371-2
detrital organic nitrogen, 371-2
detritus, 348, 375, 400, 907-08, 1081-4,
1087
Dezhnev, 807
Diamphiodia craterodmeta, 1231, 1235,
1240
Diaphus theta. All
diatoms, 375, 757-8, 773, 778-9,
936,938-41,980, 984,1116
dichothermal layer, 359, 362, 363,
371
dinitrogen oxide, 911
dinoflagellates, 375, 941, 980
Diomede Islands, 706, 785, 792, 816-
17, 819; see also Big Diomede Island,
Little Diomede Island
Diomedea spp., 694
directa, Navicula, 778
disphotic layer, 981
distorts, Navicula, 778
distichus, Fucus, 1117-18
Disturbed Belt, 294
diterpanes, 392, 402
divergence fronts, 689
diversity, species, 1105
dodecaedron, Occella, 483
dolphins, 819
dominica, Pluvialis, 721-4, 727, 733,
736
Double-crested Cormorant, 651-2, 700
Dovekies, 707, 710
Dover sole, 1029
droebachiensis, Strongylocentrotus,
1134-8, 1142-3, 1151, 1236
Dungeness crab, 1038
Dunlin, 721-6,733-6
Dutch Harbor, 1037
DYNUMES model, 612-24
E
East Coast blue crab, 1037
east Kamchatka current, 362-3
eburnea, Pagophila, 701, 800-3
Echinarachnius parma, 310, 1079,
1086, 1231, 1232, 1236, 1240
echinata, Boltenia, 1236
echinoderms, 817, 1133-7, 1232-4
echinosoma, Evasterias, 1134, 1141,
1147-9,1151, 1236
echiuroid worms, 561
Echiurus echiurus alaskensis, 1231
ecological efficiency, 872-3
ecosystem dynamics, 611-4
Ectoprocta, 1137
eddies, 8, 10, 55, 68
edulis, Mytilus, 1121-2
eelgrass, 389, 401, 513, 743, 747, 799,
1097, 1137
eelpout, 450, 480, 637, 815-6, 830,
1238-9
Egegik Bay, 182, 839-40
Egegik River, 44, 308
eggs, fish, 475-90; walleye pollock,
993-1012
Egregia, 1120
eiders, 745, 800
Ekman convergence, 48
Ekman current, 55
elassodon, Hippoglossoides, 487, 1028-
9, 1232, 1235, 1238, 1241
Eleginus gracilis. All, 528, 815-17,
819, 827-30, 1005, 1242
Eleginus spp., 774
Elymus spp., 747
Emperor Goose, 745, 747
Empetrum nigrum, 746
energy, pinniped, 871-5, 879-80, 886-
91; levels, 109
energy flow, biological, 348
Engraulis mordax, 641
enteriditis. Salmonella, 903
Enterobacter, 904
Enteromorpha spp., 1119
eous, Haustorius, 311
Ephydridae,726
Epilabidocera amphitrites, 947
epontic plants, 758
equilibrium yield, 1032-3
Erignathus barbatus, see bearded seal
Erilepis zonifer, 481
Erimacrus isenbeckii, 1061, 1232, 1234
erosion, 251, 269
Escherichia spp., 904, 905, 907
Eschrichtius robustus, 808, 819, 825,
828-33, 1318
ethane, 91, 411, 413, 418-19, 422, 425,
431, 433-6,437,440
ethene, 411, 413, 418-19, 422, 425,
431, 433-5, 437, 440
Etolin Strait, 44, 126, 180-2
Eualus spp., 637, 817, 828, 1242
Eucalanus bungii bungii, 770, 947, 950-
3,955
Eukrohnia hamata, 950-2
Eumetopias jubata, 655, 666, 818
euphausiids, in alcid diet, 710; in auklet
diet, 638-9, 641-4, 706, 708, 832;
in cormorant diet, 644; in Dall
porpoise diet, 831; distribution, 947,
950, 959, 984, 1317; in flathead sole
diet, 1241; in Fork-tailed Storm-
Petrel diet, 631, 644; hydrocarbons,
384; ingesting phytoplankton, 941,
942; in kittiwake diet, 632-5, 641,
642, 644; in mammal diet, 770; in
murre diet, 636-7, 641, 644; in
Northern Fulmar diet, 631, 641,
644; in Pacific herring diet, 510,
515-6; in ringed seal diet, 818; in
seabird diet, 770; in shearwater diet,
631, 644, 696, 1319; in spotted seal
diet, 815; in tern diet, 704; in
walleye pollock diet, 541, 838, 1238;
in whale diet, 826-8, 831-2; in
yellowfin sole diet, 560, 1241
euphotic layer, 981, 984
Eurytemora spp., 947, 951-2
Eusirus spp., 829
Evadne, 951-2
Evasterias spp., 1134, 1141, 1147-9,
1151, 1234, 1236
evermanni, Atheresthes, 487
fabricii, Eualus, 637, 1242
fabricii, Lumpenus, 485
Fairway Rock, 657
False Pass, 745
Farallon Islands, 674
fasciata, Phoca, see ribbon seal
fasciola, Gyrosigma, 778
fast ice, 167-86, 783, 785
1328 Index: fatty acids
fatty acids, 375-7
faults, 296-300
femorata, Pontoporeia, 1079, 1086
filicornis, Spio, 310
filiformis, Potamogeton, 748
fimbria, Anoplopoma, 481-2, 960,
1020-1, 1023, 1026-9, 1239
fin whale, diet, 826-7, 831
finestructure, 10, 31, 41-2, 44, 46,
350
finfish, 597-609
fischeri, Somateria, 747, 749
fish, in alcid diet, 710; in auklet diet,
638-9, 641, 644; in cormorant diet,
632, 641, 644, 700; in Dall porpoise
diet, 831-2; effect of oil spill, 1308;
eggs, 475-90; feeding at sea ice,
769; in Fork -tailed Storm-Petrel diet,
631, 698, 641, 644, 694; in Glaucous
Gull diet, 701; in Glaucous-winged
Gull diet, 701; in kittiwake diet,
632-5, 641, 644, 701, 862; larvae,
distribution, 475-90; in mammal
diet, 623, 770; in murre diet, 635-7,
641, 644, 704, 862; in northern sea
lion diet, 857, 861; in puffin diet,
639-41, 644, 708; in seabird diet,
632, 674, 770, 799, 802; in seal diet,
814-17, 856-8, 861; in shearwater
diet, 631, 644, 696; in snail diet,
1 224 ; in tern diet, 704 ; in whale diet,
826-30, 832
fisheries, 7, 11; crab, see crab fisheries;
effect on benthos, 1082; effect on
whales, 832; history, 448-51, 1016-
26; interaction with pinnipeds, 869-
70; Japan, 511, 542, 554-5, 1017-21,
1025-30; management, 624, 809,
870; oceanography, 447; regulation,
1030-4, 1041; Republic of Korea,
542, 1017, 1023;Taiwan, 542, 1017,
1023; Union of Soviet Socialist Re-
publics, 542, 554-5, 557, 1017,
1021-3, 1025, 1029
Fisheries Conservation and Manage-
ment Act, see United States Fishery
Conservation and Management Act
Fisheries Management and Protection
Act, 809
fissiped, see polar bear
flagellates, 941
flatfish, 815, 817, 830, 1115, 1238
flathead sole, 487, 1028-9, 1232, 1235,
1238, 1241
flatworms, 516
flauipes, Tringa, 7 29
flaw lead, 168-70
Flesh-footed Shearwater, 696
flexuosa, Thyasira, 1173
floccosa, Odonthalia, 1118
floes, see ice floes
flooding, 251, 258, 269
flounder, 487-9, 960, 1019, 1021,
1026-7, 1029
flow regimes, 53, 71-2, 95-110, 463-5
fluctuosa, Gomphina, 1239
fluctuosa, Liocyma, 1239
fluctus, Proechinophthirius, 903
fluoranthene, 404
fluorene, 404
food, availability, 689; competition,
818-22; partitioning, 630
food chain, 375, 712-13, 759, 869,
904,907
food web, 510, 527, 540-2, 770, 814,
817-22, 831-3, 933, 959-60, 983-4,
1084, 1242-5,1312-13
forbesii, Travisia, 310, 1240
Fork-tailed Storm-Petrel, 631, 644, 651,
694,698-700,712
Forrester Island, 672
fossa, Nuculana, 1159, 1161, 1166,
1169, 1171, 1173, 1176-83, 1233
fourhorn poacher, 483
fox, 708; see also arctic fox
Fox Island, 837-9
Fragilaria spp., 778, 936
Fragilariopsis spp., 936
fragilia, Bacteriosira, 936
fragilia, Volutopsius, 1217, 1219-20
Fratercula arc tica, 67 2
Fratercula
Fratercula arctica, 672;
Fratercula corniculata, 639-41, 644,
672-3, 676, 708, 712
freshwater influx, 19, 55, 68, 90-1,
347,426
frigida, Nitzschia, 778, 936
fronts, 10, 31, 37-41, 46, 49; oceano-
graphic, 306, 309; shelf, 426, 995;
effect on benthic fauna, 1092, 1100;
effect on nutrients, 975-6, 984,
1092; effect on seabird distribution,
690, 700, 711-12; effect on zoo-
plankton, 951, 953, 955, 959;
temperature, 767
fucose, 374-5
Fucus spp., 513, 1116-19
fulicarius, Phalaropus, 700, 721, 730
fulmars, see Fulmarus glacialis
Fulmarus glacialis, 630-1, 641, 643-4,
650-1, 679, 690, 694-6, 711-13,
800, 802
fur seal, see northern fur seal
Fur Seal Act, 858
furcata, Oceanodroma, 631, 643-4,
651, 694, 698-700, 712
fusca, Melanitta, 7 50
fuscum, monostroma, 1116
Fusitriton oregonensis, 1222-3
G
gadfly petrels, 698
gadids, see Atlantic cod, haddock. Pacif-
ic cod, saffron cod, walleye pollock
Gadus macrocephalus, see Pacific cod
Gadus spp., 774, 1007-8, 1238
gaimardii, Eualus, 828, 1242
galactose, 374-5
Gallinago gallinago, 7 31
Gambell, 816
gas cratering, 256-7
gastropods, 829, 907, 1215-26, 1232,
1236
geology, 293-300, 1156, 1268, 1287-
90
gigas, Grossotrea, 907
glacialis, Arctogadus, 11 A, 799
glacialis, Calanus, 110
glacialis, Fulmarus, 630-1, 641, 643-4,
650-1, 679, 690, 694-6, 712, 800-01
glacialis, Liopsetta, 919
glacialis, Parosira, 936
glandiforme, Halosaccion, 1116
glandula, Balanus, 1121-2
glaucescens, Larus, 655-6, 678, 701,
801
Glaucous Gull, 655, 701, 800-2
Glaucous-winged Gull, 655-6, 678, 701,
801
Global Navigation System, 202
glucose, 374-5
glutamic acid, 373
glycine, 373
Glyptocephalus zachirus, 1232
golden king crab, 1040, 1061
golden triangle, 348
Golovnin Bay, 178, 511, 514, 584-5,
748, 785
Gomphina fluctuosa, 1239
gonatids, 829
goniurus, Pandalus, 828, 1236, 1242
goodei, Ptilichthys, 486
Goodnews Bay, 182, 664, 731
gorbuscha, Oncorhynchus, 575-86, 591,
608, 1238
Gorgonocephalus spp., 1134-6, 1138,
1143, 1149, 1151, 1232
gracilis, Eleginus, All, 528, 815-17,
827-30, 1005, 1242
Grantley Harbor, 511, 514,785
gravel, 307-8, 310
gravida, Thalassiosira, 940
gravis, Puffinus, 690
gray whale, 808, 819, 825, 828-33,
1318
grease ice, see ice
great sculpin, see sculpin
Greater Scaup, 748
Greater Shearwater, 690
Greater Yellowlegs, 7 29
green sea urchin, 1134-8, 1142-3, 1151
Greenland, 1080
Greenland cockle, 817, 1080, 1084,
1151, 1173, 1236-7, 1239, 1242
Index: ice 1329
Greenland halibut, 489, 816, 960,
1020-1, 1023, 1026-9, 1238-40
Greenland turbot, see Greenland halibut
greenling, 480-1, 815, 827
grenadier, 480, 829
griseus, Limnodromus, 721, 731, 736
griseus, Puffinus, 631, 643-4, 650,
694, 696-8, 712
groenlandica, Phoca, 788, 87 2, 883
groenlandicus, Serripes, 817, 1080,
1084, 1151, 1173, 1236-7, 1242
Grossotrea gigas, 907
grounded-ridge zone, 168-71
grunowii, Nitzschia, 778, 936
grylle, Cepphus, 650, 668,710,800-01,
803
Gulf of Anadyr, 32, 33, 55, 451;dicho-
thermal layer, 362; halibut, 496;
ice formation, 785; ribbon seal,
815; salinity, 461-2; salmon, 578,
581-3, 586, 608; temperature, 601-
03; walleye pollock, 527; yellowfin
sole, 553
Gulf of Bothnia, 600
Gulf of Finland, 600
Gulf of Olyutorski, 516
Gulf of St. Lawrence, 197, 1235
gulls, 654, 676, 700-04;
gunnel, 486
Gymnocanthus spp., 483
Gymnodinium spp., 980
Gyrosigma spp., 778, 936
H
habitat, marine mammal, 787-94;
shorebirds, 734-6; waterfowl, 739-
50
haddock, 1007
haemastica, Limosa, 7 27-8
Hafnia, 904
Hagemeister Island, 675, 748
Hagemeister Strait, 514
hake, 831
halibut, see Greenland halibut. Pacific
halibut; see also Hippoglossus hippo-
glossus
Hall basin, 296
Hall Island, 668, 670, 674, 694
halocline, 765, 767
Haloconcha reflexa, 1119-20
Halosaccion spp., 1116-19
hamata, Eukrohnia, 950
harbor porpoise, 808, 825, 830-2, 861-2
harbor seal, 384, 808, 813-15, 818,
873, 883-8, 891, 1238-9, 1241-2,
1318
harengus pallasi, Clupea, 449, 451-2,
475-6, 510-22, 831, 1020, 1023
Harlequin Duck, 749
harp seal, 788, 872, 883
Haustorius eous, 31 1
Hazen Bay, 180, 730
heavy metals, 313-16, 339-45
Hedophyllum spp., 1116-17
helianthoides, Pycnopodia, 1234
helicinus, Margariles, 1119-20
heliozoans, 774
helium, 437
Hemilepidotus spp., see sculpin
heneicosahexane, 384
Herald Arch, 294, 297, 298
Herald Fault Zone, 294, 296-7
herbivores, 1118-19, 1124
Herendeen Bay, 517
hermit crabs, 1239
heros, Neptunea, 1134, 1136-9, 1151,
1219-20, 1223-4
herring, 642; abundance, 449, 451;
migration, 598-604, 606; in pinniped
diet, 819; in porpoise diet, 831; in
seabird diet, 642, 675; in seal diet,
815, 819, 870, 1242; spawning,
601-02, 604, 606, 608; in walleye
pollock diet, 1238; in whale diet,
827-31 ; see also Pacific herring, other
specific herring
Herring Gull, 650, 654, 701
Heteroscelus incanus, 729
Hexagrammidae, 480-1
Hexagrammos spp., 480-1, 815, 827
hexane, 392, 401
hexapterus, Ammodytes, see sand lance
Hiatella spp., 817-18, 1084, 1238
highsnout melamphid, 480
Hinchinbrook Island, 663
Hippoglossoides spp., 487, 1232, 1241
hippoglossoides, Reinhardtius, 489,
816, 960, 1020-1, 1023, 1026-9,
1238-40
Hippoglossus hippoglossus, 496
Hippoglossus stenolepis, see Pacific
halibut
Hippomedon, 1279
hirundo. Sterna, 704
hispida, Phoca, 759, 788-9, 792-4,
808, 813, 816, 818, 832, 1242
Histrionicus histrionicus, 749
Hokkaido Island, 496, 553, 581
holothurian, 907
holoplankton, 950
hooded seal, 788
hookhorned sculpin, 483
Hooper Bay, 730, 873
hopanes, 403
Hope basin, 294, 296, 298, 300, 826
Horned Puffin, 639-41, 644, 672-3,
676, 708, 712
horse crab, 1234; see also Korean hair
crab
Hotham Inlet, 514, 518
Hudsonian Godwit, 727-8
humic acid, 401, 404
hummock fields, 170, 172
humpback whale, 808, 825, 827-8,
830-1
humpy shrimp, 1236
hunting, 807
Hyas spp., 817, 829, 1232, 1238-9
Hydrobatidae, 651
hydrocarbons, dissolved, 426-7; gas, 256,
411-22, 435; of marine animals,
383-7; in marine sediments, 389,
392-4, 399-402, 434; petroleum-
derived, 434, 436; source-compo-
sition relationship, 434-40; utilizers,
904
hydrogen sulfide, 911
hydrography, 32, 213, 359, 361-3;
distribution, 7; domains, 31, 33-7,
49, 53, 72, 950; profilers, 5, 34;
structure, 31-50
hydroid, 907
Hydrozoa, 950
hyemalis, Clangula, 745, 749-50, 800
hyperborea, Yoldia, 1231, 1239-40
hyperboreus, Larus, 655, 701, 800-02
hyperiid amphipod, 631
Hypsagonus quadricornis, 483
ice, advection, 170-1, 213, 217-18;
algae, 758, 759, 763, 773-9; bands,
142, 145, 152-3, 155, 164, 172,
179-80, 189, 197, 202-04, 207-1,
210, 213; behavior, 186; bloom,
778; brash, 149, 778, 787; breakup,
269-75, 399, 455, 457, 465; compac-
tion, 142, 147, 149, 179; conditions,
282; cores, 145, 152, 189; cover, 68,
70, 73, 78, 123, 133, 135-7, 142,
455, 457-8, 466, 598-604, 611,
764-5; cycle, 135; decomposition,
801-03; deformation, 269, 787;
depth, 168; disintegration, 770-1,
787; dissipation rate, 136; diver-
gence, 142, 149; dynamics, 216, 264,
282, 1311-12;edge, 152-5, 164, 167-
72, 178-86, 189-92, 194, 202,
598-604, 763-71; effect on benthos,
759; effect on petroleum develop-
ment, 264; effect on salt, 49; effect
on seabirds, 799-803; extent, 23, 24,
32, 164, 782, 800-01, 803; fast,
167-72, 178-86, 189-92, 783, 785;
first-year, 141-2, 147, 172; floes,
155, 189, 192-5, 197-210, 213,
785-7; flora, 758; fluctuations, 133;
formation, 135, 136, 142, 145-7,
213. 399, 455, 457, 465, 783, 786,
800, 803; formation of floes, 203;
1330 Index: ice, cont.
ice, cont.
freezeup, 265; front, 800-803; gen-
eration, 142, 763; gouging, 253-4,
258, 264-5, 275, 279, 283-9, 400;
grease, 145-7, 216, 223, 225-31;
hazards, 275-6; interior zone, 189,
194, 197; jams, 269; melting, 133,
135-6, 142, 160-2, 164, 209-10, 214,
216, 763; migration, 16, 135, 141-
2, 145, 147, 149, 151-3, 155, 164,
172, 203-04, 207, 210, 216-18,
237; movement, 267-9, 275, 282;
multiyear, 167; nearshore, 167, 172,
178-86, 189-92; pack, 133, 142, 155,
168, 170-2, 179, 182, 186, 189, 194,
197, 202, 210, 218, 282, 286, 565-6,
783, 785; pancake, 145, 155, 204,
207, 231-2, 235-7; plumes, 225-7;
rafted, 149, 155, 182, 189, 192,
197, 202, 210, 216, 224; retreat,
133, 136-7, 142, 160-4; ridges, 149,
168-71, 178, 189, 192, 202, 210,
216-17, 224; rotting, 142, 152, 155,
216-17; scour, 253-4, 258, 1106,
1111-25; sheet, 155, 167, 170, 782-
3; spatial distribution, 1108; stream-
ers, 142, 145; temporal distribution,
1108; thickness, 782; trajectories of
floes, 164; transition zone, 189,
192, 194, 202; transport, 45, 783
Icelinus borealis, 483
ichthyoplankton, 471-90
illite, 311-13
immutabilis, Diomedea, 694
Imuruk Basin, 514, 518
incanus, Heteroscelus, 729
Indigirka River Delta, 749
inermis, Thysanoessa, 632-3, 637, 639,
770, 826-7, 950-2, 959, 1238
inertial-gravity waves, 126
inexpectata, Pterodroma, 690, 698,
712
insolation, 90-1, 457, 466
Interim Convention on Conservation of
North Pacific Fur Seals, 848
International Convention for the High
Seas Fisheries of the North Pacific
Ocean, 495
International Fisheries Commission
(IFC),495
International North Pacific Fisheries
Commission (INPFC), 451, 457,
495, 504, 1030, 1039-40
International Pacific Halibut Commis-
sion (IPHC), 495-6, 504, 1030,
1033
interpres, Arenaria, 726, 729-30
invertebrates, 633, 636-40, 642, 1121-2
Irish lord, 482
iron, 314-17, 324, 332-3
isenbeckii, Erimacrus, 1061, 1232, 1234
islandica, Fragilaria, 118, 936
Islands of the Four Mountains, 671
isobutane. 411, 418-19, 422, 425
isoleucine, 373
isopods, 829
Ivory Gull, 701, 800-01, 803
Ixodes uriae, 904
IXTOC-I blowout oil spill, 237
Izembek Bay, 744-5, 747
Izembek Lagoon, 353, 389, 392, 401,
404, 434-5, 743-4, 746, 839-40,
844, 1097
Izhut Bay, 1231, 1233
Jacksmith Bay, 182
jaegers, 700
Japan, crab fishery, 1039-40, 1045-7,
1054-60; fisheries, 511, 542, 554-6,
1017-21. 1025-30; fishery agree-
ments, 495, 505, 1030-31, 1040;
snail fishery, 1215, 1224-6
Japanese Fishery Agency, 1215
japonica, Asterophila, 1150
japonica. Babylonia, 1224
jellyfish, 384, 631
joak, Myoxocephalus, 1239
johanni, Yoldia, 1239
jubatus, Eumetopias, 655, 666, 818
K
Kachemak Bay, 721, 1234
Kaligagan Island, 673
Kaltag fault, 294, 296-300
Kamchatka flounder, 487
Kamchatka Peninsula, 8, 501, 527,
671, 694,749
Kamishak Bay, 1234
kaolinite, 312
Karaginsky Bay, 789
Karaginsky Inlet, 749
Katharina tunicata, 1119
keta, Oncorhynchus, 575-86, 591, 608,
1238
Kilbuck Mountains, 731
Kiliuda Bay, 1231, 1233
killer whale, 794, 808, 825, 829-32,
858-9
kincaidi, Malacocottus, 483
kinetic energy, 59-64, 67-9, 71, 73
king crab, diet, 1155, 1176, 1235;
distribution, 1133, 1144; fishery,
1037-9, 1047, 1056-7, 1131, 1144-5;
food web, 1231, 1233; in halibut
diet, 1239; pot sanctuary, 1030;
predators, 1234; in sea otter diet.
king crab, cont.
1234; in sperm whale diet, 829; see
also blue king crab, golden king crab,
red king crab
King Eider, 745, 748-9
King Island, 255, 649, 669-70, 675,
706,785, 791
King Salmon, 186, 1097
king salmon, 602, 607-08
kisutch, Oncorhynchus, 575-80, 582-3,
585-6, 591, 608, 1238
kittiwake, 641-2, 650, 656, 677-9,
802,862
Kittlitz'sMurrelet, 710
Kivalena, 225
Kobuk fault, see Kobuk Trough
Kobuk River, 103, 296
Kobuk Trough, 294, 296-300
Kodiak, 106. 109
Kodiak Island, 657, 663-5, 749, 1039,
1041, 1231, 1233,1235, 1239
Komandorsky Islands, auklets, 671,
706; fulmars, 650, 694; Glaucous-
winged Gull, 655; harbor seal,
873; kittiwakes, 662, 703; northern
fur seal, 850; storm-petrels, 698
Kongkok Bay, 637
Korea, see Republic of Korea
Korean hair crab, 1061, 1232, 1234
Kotzebue, 105-06, 109, 167
Kotzebue anticline, 298
Kotzebue Sound, 90, 103, 225; beluga
whale, 830; herring, 512, 518, 602;
ice formation, 225; murres, 704;
salinity, 45; salmon, 580-3, 586
Koyuk,7 27
Krenitzin Island, 837-9
kroyeri, Plicifusus, 1219-20
Kulukak Bank, 449
Kurile Islands, 361-3, 527, 650, 668,
671-2, 850
Kuskokwim Bay, 44-5, 56; Black
Scoter, 750; fast ice, 182; methane
source, 428, 430; Pintail, 748; salin-
ity, 45; salmon, 581, 583, 586;
Taverner's Canada Goose, 746; tides,
117; walrus, 789; yellowfin sole,
563
Kuskokwim Delta, see Yukon Delta
Kuskokwim River, 32, 743, 1080;
American Golden Plover, 727; cur-
rent, 456; detritus, 1097; fast ice,
182; as freshwater source, 19, 426,
460; goose, 746-7; herring, 511,
516; lipids from, 399; Long-billed
Dowitcher, 731; methane source,
429; salmon, 582; sand source,
308; Semipalmated Sandpiper, 732;
transport of terrigenous material,
400;Whimbrel, 728
Kvichak Bay, 126-7
Kvichak River, 32, 44, 308, 426-7,
582, 1156
Index: mollusks 1331
lactuca, Ulua, 1116
Lafoeina maxima, 1233
lagopus, Alopex, 677, 788-9, 858
lamellibranch, 907
Laminaria spp., 1116-18, 1124
lamprey, 830
lancet, 829
lanternfish, 477
lapponica, Limosa, 721-6, 728, 732
larga seal, see spotted seal
largha, Phoca, see spotted seal
Laridae, 654-65
Larus spp., 641, 650, 654-6, 700-01,
799-802
larvae, 611, 1109
larval fish, 475-90, 706
layering, 79-84, 88, 90
Laysan Albatross, 694
Leach's Storm-Petrel, 651, 694, 698-
700,712
lead, 314, 339
Least Auklet, 638-41, 644, 670-1,
674, 694, 706-08, 712
Least Sandpiper, 726, 732-3
Leda, 1232
Lembos spp., 829
Lena River, 576
Lepidopsetta bilineata, 488, 490, 561,
919-20, 1028-29, 1235, 1240
Leptasterias polaris acervata, 1134,
1137, 1141, 1146-7, 1149-51, 1236
leptospira, 903-04
lesions, in Pacific cod, 923-4
lesser prickleback, 485
Lesser Snow Goose, 745, 747
Lesser Yellowlegs, 729
Lethasterias nanimensis, 1134, 1141-2,
1147, 1151, 1236
leucas, Delphinapterus, 623, 759, 774,
788, 791-4, 808, 830-1
leucichthus, Stenodus, 514, 518
leucine, 373
leucopareia, Branta canadensis, 748
leucopsarus, Stenobrachius, 477
leucorhoa, Oceanodroma, 651, 694,
698-700, 712
libellula, Parathemisto, 631-7, 639,
642,770, 828, 1238
limacina, Ophelia, 310
Limanda aspera, see yellowfin sole
Limanda proboscidea, 488, 553, 1028,
1029
Limnodromus spp., 721-4, 726, 731,
735,736
Limosa spp., 721-4, 726-8, 732, 735
limpets, 1119
Lincoln Bight, 844
Liocym'a fluctuosa, 1239
Liopsetta glacialis, 919
liparids, 451
Liparis spp., 484
liquefaction, 253, 257-8
Lisburne Hills, 294, 297-9
Lithodes aequispina, 1040, 1061
Little Diomede Island, 634, 649,
657,669-76, 783, 791, 816
little piked whale, 808, 825, 828, 830-2
littorea, Littorina, 1119
Littorina spp., 1119-20
lobatus, Phalaropus, 700, 721, 730
lomvia, Uria, see Thick-billed Murre
longasetosa, Nephthys, 310
Long-billed Dowitcher, 721, 726, 731,
735, 736
longhead dab, 488, 553, 1028, 1029
longicaudus, Stercorarius, 700
longipes, Laminaria, 1117-18, 1124
longipes, Thysanoessa, 632-3, 637,
770,826
longiremis, Acartia, 940
Long-tailed Jaeger, 700
lucens, Metridia, 770
Lumpenus spp., 485, 636, 816, 1231
lumpsuckers, 484, 829
Lunda cirrhata, 639-41, 643-4, 673-4,
676-7, 862
lutea, Tellina, 1151, 1159, 1167-8,
1173, 1183, 1236, 1240
Lutra canadensis, 677
Lycodes spp., 450, 480, 637, 815-16,
830, 1238-9
Lyconectes aleutensis, 486
lymphocystis, 926-8
lyrata, Neptunea, 1219, 1222-4
lyratus, Hyas, 1239
lysine, 373
M
Mackenzie River Delta, 831
mackerel, 831
Macoma balthica, 7 26
Macoma calcarea, 1159, 1167, 1173-
4,1176-83,1236
Macoma spp., 1234, 1235, 1305
macouni, Chauliodus, 477
macrenteron, Styela rustica, 1143
macrocephalus, Gadus, see Pacific cod
Macrouridae, 480
maculatus, Lumpenus, 485
magister. Berry teuthis, 858
magister, Cancer, 1038
magna, Clinopegma, 1219-20
magnesium, 324, 332
Magnuson Fishery Conservation and
Management Act, 1017: see also
United States Fishery Conservation
and Management Act
Malacocottus spp., 483
Mallotus spp., 631-7, 661, 700, 827,
891. 1233
Mandarte Island, 652-3, 656
manganese, 314-15, 321, 324, 332-5
mannose, 374-5
Marbled Murrelet, 710-11
Margarites spp., 1119-20, 1233
marila, Aythya, 748
marina, Zostera, 401, 404, 1097
marine birds, 627-753, 759, 1318-19
Marine Mammal Protection Act, 808-09,
870
maritimus, Ursus, 788-92, 794, 808
marmoratus, Brachyramphus, 710-11
marshallae, Calanus, 639, 770
Massachusetts Bay, 224
maxima, Lafoeina, 1233
maximum sustainable yield, fish, 1029,
1032-3
media, Siliqua, 1239, 1241
Mediaster aequalis, 1109
medius, Lumpenus, 485
Medusae, 384
Megaptera novaeangliae, 808, 825, 827-8,
830-2
Melamphaeidae, 480
Melamphaes lugubris, 480
Melanitta spp., 750
melanocephala, Arenaria, 721-4, 730,
735
Melanogrammus aeglefinus, 1007
melanoleuca, Tringa, 729
melanotos, Calidris, 7 22-4, 726, 7 33
Melita, 1279
Melosira sulcata. 111
meltback, 133-6, 141, 142, 160-4,
209, 214, 216
meltwater, 155, 214-15, 216
meroplankton, 950
Mesoplodon stejnegeri, 825, 830-1
metabolism, pinniped, 871, 875-7, 880-
3,887-8
methane, 91, 256, 411, 413, 418-
22, 425-40, 911
methionine, 373, 910
Metridia spp., 770, 947, 950, 953,
955
Mew Gulls, 650, 654, 700-01
microalgal carbon, 401
microbes, 903-12
microflagellates, 936
micronekton, 947, 1313
Middleton Island, 667
migration, seasonal, 611, 613, 618-19;
shorebird, 725, 726; waterfowl, 739-
40, 744
minima, Branta canadensis, 745-7
minke whale, 808, 825, 828, 830-2
minutilla, Calidris, 726, 732-3
Moffet Lagoon, 840
Mogula sp., 1097
mollissima, Somateria, 748-9
mollusks, bivalve, 1070, 1073, 1160-
73; distribution, 1110-11, 1133,
1137; gastropod, 1073; in herring
diet, 516; in plaice diet, 1239;
predators, 1246-7; in red king crab
diet, 1232, 1234; in seabird diet,
799; in Tanner crab diet, 1235;
see also specific mollusks
1332 Index: molt, pinniped
molt, pinniped, 884-8
monocerata, Cerorhinca, 650, 710-11
Monodon monocerus, 759-88
monopterygius, Pleurogrammus, 480,
815, 827-31
monosaccharides, 375
Monostroma spp., 1116
Montipora verrucosa, 907
Moraxella, 904
mordax, Engraulis, 641
mordax, Osmerus, 476
morphology, Bering Sea, 247-8
morrhua, Gadus, 1007-08
Moses Point, 748
Mottled Petrel, 690, 698, 712
murres, 674; colonies, 655; diet, 862,
1238, 1313; distribution, 711-13,
801; food web, 1313; habitat,
650, 656; migration, 800; repro-
ductive success, 677-8; see also
specific murres
murrelets, 650
Muscidae, 726
musculus, Balaenoptera, 827
mussels, 830
Mya spp., 817, 1070, 1084, 1238
myctophids, 477, 632-6, 641, 662,
676,703-04
Myoxocephalus spp., see sculpin
mysids, 560, 814-16, 828-9
Mysis oculata, 828
mysticetes, see specific whale
mysticetus, Balaena, 623, 788, 791-4,
807-08, 825, 828, 831
Mytilus spp., 907, 1121-2, 1305
N
Naked Island, 663
Naknek River, 44, 182, 308, 582
nanimensis, Lethasterias, 1134, 1141-2,
1147, 1151, 1236
Nanvak Bay, 728
naphthalenes, 404
narwhal, 759,788
Natica clausa, 1236
Naticidae, 637
natriegens, Pseudomonas, 905
naupiii, 541, 955
Navicula spp., 778, 936
n-butane, 411, 418-19, 422, 425
Nectoliparis pelagicus, 484
Near Islands, 671
nekton, 401, 690
Nelson Island, 179, 182
Nelson Lagoon, 723, 728, 730-1
nematodes, 774
Neomysis rayi, 384
Nephlhys spp., 310
Neptunea heros, 1134, 1137-9, 1151,
1219-25
Neptunea spp., 817, 1215, 1219-25
nereid worms, 636, 639, 708
Nerita picea, 907
nerka, Oncorhynchus, 450, 575, 578-
86, 591, 602, 605, 608, 959
nesting, see habitat, specific seabirds,
waterfowl
neuston, 690, 1006
nickel, 324, 332
nigra, Ascidia, 907
nigra, Melanitta, 750
nigricans, Branta bernicla, 743-5, 747
nigripes, Diomedea, 694
nigrum, Empetrum, 746
nitrate, 351, 353, 767-70, 775-6,
779, 976-88
nitrite, 353
nitrogen, 324, 332, 360; cycle, 910-12;
detrital organic, 371-2; effect on
phytoplankton growth, 362; fixa-
tion, 907-12; particulate organic,
360-6; in seawater, 939; source, 779,
981
Nitzschia spp., 778, 936, 941
Noatak River, 103
Nome, 105-06, 109, 186, 226, 253,
258, 816, 1141
normanii, Pleurosigma, 778
North Pacific Fishery Management
Council, 1032, 1033, 1041, 1053
North Pacific Fur Seal Convention, 807
Northeast Cape, 17-18, 127
northern anchovy, 641
Northern Fulmar, 630-1, 641, 650,
679, 690, 694, 696, 712, 800-01
northern fur seal, 601, 607, 623,
808, 818, 847-63, 873, 1313
northern lampfish, 477
Northern Phalarope, 700, 721, 7 ?0
northern sculpin, 483; see also sculpin
northern sea lion, see sea lion
northern smoothtongue, 476
Northwest Cape, 127
Norton basin, 251-3, 294, 296, 298,
300, 420, 826, 828
Norton Bay, 178, 225, 310, 785
Norton Sound, 77-9; acoustic anomaly,
420; amphidrome, 117, 119, 122,
127; auklets, 669; beluga whale,
830, Black-bellied Plover, 727; bu-
tanes, 431; Common Snipe, 731;
cormorants, 653; crab fisheries,
1041, 1044-5; description, 743;
Dunlin, 734; fast ice, 178; fulmars,
694; gas craters, 256-7; gas seep,
435, 437, 440; geology, 411-13;
Glaucous Gull, 655; godwits, 727-8;
herring, 514, 516, 519, 600-01,
604; hydrocarbon gases, 411, 418-
20; ice cover, 78, 142, 179, 216;
ice formation, 216, 225, 785; ice
movement, 282; ice regimen, 265;
kittiwakes, 658; layering, 79-84, 88,
Norton Sound, cont.
90; Long-billed Dowitcher, 731;
murres, 665-7 ; organic carbon con-
tent, 392, 394; Pacific herring,
476; pack ice, 265-7, 269; phala-
ropes, 730; Pigeon Guillemot, 668;
puffins, 672; Red Knot, 731; ringed
seal, 816; salinity, 45, 461, 602-03;
salmon, 580-6, 608; Sanderling, 732;
sandpipers, 732-4; scour depressions,
2545, 257-8 ; sea otter, 845 ; seabirds,
675, 678; sediment, 251, 258, 269,
310, 323; shorebirds, 726; starry
flounder, 1240; storm regimes, 251-
3; Surf bird, 731; Tanner crab, 1235;
tides, 117. 119. 123-7, 248, 251;
turnstones, 730; water level, 108-09;
wave effects, 253
Notoacmaea spp., 1119-20
novaeangliae, Megaptera, 808, 825,
827-8, 830-2
Nucula spp., 1159-61, 1166, 1167,
1169, 1170, 1173-4, 1176-83, 1231-
3,1235
Nuculana spp., 1159, 1161, 1166,
1168, 1169, 1170, 1171, 1173-4,
1176-83, 1232-5, 1238
nugax, Anonyx, 637
Nulato Hills, 728
Numenius spp., 726, 728-9
Nunivak Island, 32, 43, 45, 54, 65, 66,
1156; American Golden Plover, 727;
amphidrome, 117, 119, 122; Black
Brant, 745; clams, 1171; eiders,
748-9; Glaucous Gull, 701; Glaucous-
winged Gull, 655, 701; goose, 745-
6; Harlequin Duck, 749; herring,
601; humpback whale, 827; ice
cover, 142, 600; ice formation, 225-
786; ichthyoplankton, 475-90; mar-
ine birds, 675, 713; murres, 676,
705; Pacific cod, 477-8; polynyas,
216; sea otter, 845; terns, 663; tides,
123; walrus, 789; Western Sandpiper,
732;yellowfin sole, 5623, 603, 608
Nunivak National Wildlife Refuge, 747
Nushagak Bay, 126
Nushagak River, 308, 399, 427, 460,
582, 1156
nutrients, benthic fauna, 1073; concen-
trations, 975-6, 983-4, 987-8; diet
content, 874-5; inorganic, 368
o
Occella dodecaedron, 483
occidentalis, Larus, 641, 700
Oceanodroma spp., 631, 644, 651,
694,698-700,712
ochraceus, Pisaster, 1237
\
octopus, 814-17, 830, 1238
oculala, Mysis, 828
Odohenus rosmarus, see walrus
Odonthalia floccosa, 1118
odontocetes, see specific whale or
porpoise
Odontopyxis trispinosa, 483
offal, 630-1, 694, 698, 701
oil, contamination effects, 679, 837-9,
854-5, 911-12, 1125; development
risks, 1300-04; ecological impact,
1305, 1308; in grease ice, 230,
235-7; in ice floes, 224, 231-2,
235-7; spills, 237, 1304-10
oil-ice interactions, 223-37
Oithona similis, 770, 950-1
Okhotsk Sea, 527, 553, 563, 583,
750
Oldsquaw, 745, 749-50, 800
olriki, Aspidophoroides, 483
Oncorhynchus spp., 575, 661, 815; see
also Chinook salmon, chum salmon,
coho salmon, pink salmon, salmon,
sockeye salmon
Ophelia limacina, 310
Ophiodesoma spectabilis, 907
Ophiura spp., 1086, 1231, 1232, 1235
opilio, Chionoecetes, 817, 1037, 1051-
64, 1133, 1145, 1234-5, 1238-40
optimum yield, fish, 1034
orca, Orcinus, 794, 808, 825, 829-31,
858-9
oregonensis, Fusitriton, 1222-3
Orcinus orca, 794, 808, 825, 829-31,
858-9
ornithine, 373
organic carbon, 360-7, 392-3, 434,
909-10, 1174, 1230, 1312-13
organic matter, 389, 909-10
orientate, Chelyosoma, 1236
osmerid smelt, 476
Osmeridae, 476
Osmerus mordax, 476
Otter Island, algae, 1116-21; benthic
biota, 1110; harbor seal, 815; herbi-
vores, 1119-21; ice scour, 1106;
kittiwakes, 635; sea otter, 844;
seabirds, 674; sessile invertebrates,
1121-2; species-biomass distribution,
1115
oxygen, 911, 986
Oyashio area, 361-3, 369, 690
oysters, 1306
Pacific blacksmelt, 476
Pacific cod, abundance, 528; diet,
542, 1232, 1235, 1238-9; distribu-
tion, 477-8, 1027; eggs, 1005;
Pacific cod, cent.
fishery, 1016-17, 1021, 1026-7,
1029; in harbor seal diet, 815; lar-
vae, 477-8; predators, 815, 827-30,
1239; in whale diet, 827-30
Pacific fin whale, 808; see also fin whale
Pacific Flyway swans, 746
Pacific halibut, 452, 473, 487, 830;
abundance, 503-04; description, 496,
500-02, 506; diet, 502-03, 542,
560,1234-5, 1238-9; distribution,
496-500, 506, 560; fisheries regula-
tions, 495-6, 504-05, 507; fishery,
495-6, 504-06, 1017, 1020, 1026,
1028, 1030; migration, 496-500,
506, 598-605; research, 505-07;
spawning, 500-01, 506, 598-600,
606-07
Pacific herring, 449, 451-2, 475-6,
510, 522, 561, 831, 1020, 1023;see
also herring
Pacific ocean perch, 542,959, 1020-1,
1027-9
Pacific salmon, see chinook salmon,
chum salmon, coho salmon, pink
salmon, salmon, sockeye salmon
Pacific sandfish, 1239
Pacific sardine, 674, 831
Pacific saury, 829
Pacific viperfish, 477
Pacific walrus, see walrus
pacifica, Calidris alpina, 734
pacifica, Parathemisto, 384, 950, 1238
pacificus, Artediellus, 483
pack ice, see ice, pack
Pagophila eburnea, 701, 800-03
Pagurus spp., 1232, 1235
Palmer Station, 758
Pandalus borealis, 1231-2, 1238, 1239,
1240, 1241
Pandalus go niurus, 828, 1236
Pandalus spp., 817
papillomas, epidermal, 919-28
paradisaea. Sterna, 663-5, 704
Parakeet Auklet, 638-41, 644, 669-71,
676,706-08, 712, 801
Paralithodes camtschatica, see red king
crab
Paralithodes platypus, see blue king crab
Paralithodes spp., see king crab
Paraphoxus sp., 310
Parasitic Jaegers, 700
parasiticus, Stercorarius, 700
Parathemisto libellula, 631-7, 639, 642,
770, 828, 1238
Parathemisto pacifica, 384, 950, 1238
Parathemisto spp., 704
parma, Echinarachnius, 310, 1079,
1086, 1231-2, 1236, 1240
Parosira glacialis, 936
particulate amino acids, 372-4
particulate matter, 321-2, 325-9
particulate organic carbon, 360-7, 369-
71
Index: phytoptankton 1333
particulate organic nitrogen, 360-6,
369-71
Pectoral Sandpiper, 722-4, 726, 733
pectoralis, Coryphaenoides, 480
Pelagic Cormorant, 632, 651-4, 678,
700
pelagic distribution, marine birds, 711-
13
pelagis, Nectoliparis, 484
pelagis, Phalacrocorax, 632, 651-4,
678, 700
Pelonia, 1233
pelta, Acmaea, 1120
pelta, Collisella, 1119-20, 1123
Pelvetia, 1120
penicillatus, Phalacrocorax, 650
Pennaria tiarella, 907
persona, Notoacmaea, 1119-20
perspicillata, Melanitta, 7 50
perylene, 404
Peter the Great Bay, 1238
petroleum, 7-11, 399, 402-03, 440;
see also oil
Phaeocystis spp., 936, 938, 940-2
phaeopus, Numenius, 726,728
Phalacrocoracidae, 651
Phalacrocorax spp., 632, 640-1, 650-4,
678, 700
phalaropes, 700, 721, 726; see also
Northern Phalarope, Red Phalarope
Phalaropus spp., 700, 721, 726, 730
phenanthrene, 404
Philacte canagica, 145, 747
Philadelphia, Larus, 700
Phoca fasciata, see ribbon seal
Phoca groenlandica, see harp seal
Phoca hispida, see ringed seal
Phoca largha, see spotted seal
Phoca vitulina, see harbor seal
phocid seals, see bearded seal, harbor
seal, ribbon seal, ringed seal
Phocoena phocoena, 808, 825, 830-2,
861-2
Phocoenoides dalli, 808, 825, 830-2,
861-2
Pholidae,486
phosphates, 775-6, 908, 910-11, 976-
80; concentration, 982-3, 987-8
photosynthesis, 347-8, 351-6,773,776,
778
phthalates, 384, 386
Phyllochaetopterus prolifera, 1109
physalus, Balaenoptera, 825, 826-7,
831-2
Physeter catodon, 623, 825, 829,
831-2
phytane, 392, 399, 402
phytoplankton, 366, 368, 773; bloom,
936, 938-9, 948, 951, 959, 1230,
1316-17; bloom in ice margin,
763-4, 767 ; distribution 933-7 ; effect
of bloom on acid concentration,
376-7; effect of bloom on carbon
dioxide, 355; effect of oil spill,
1305, 1308; in euphausiid diet,
826; food web, 1313; in ice, 757-9,
1334 Index: phytoplankton, cont.
phytoplankton, cont.
777-8, 936, 939-40; importance of
light, 938-40, 942; nutrients, 938-43,
975-7, 979, 988; particulate organic
carbon source, 363, 372; productiv-
ity, 983; seasonal succession, 938-43
picea, Nerita, 907
Pigeon Guillemot, 668-9, 676, 710
pingeli, Triglops, 483, 636
pink neck clam, 1151, 1159, 1171-3,
1176-83, 1205-13, 1234, 1236
pink shrimp, 1231-2, 1238, 1239, 1240,
1241
pink salmon, 575-86, 591, 608, 1238
Pinnacle Island, 674
pinnipeds, 870; see also bearded seal,
ribbon seal, ringed seal, spotted
seal, walrus
Pinnixa, 1238
Pintail, 745, 748
pipeline construction, hazards, 256-8
Pisaster ochraceus, 1237
plaice, 543, 561, 607, 1006, 1028-9,
1239; see also flatfish
plankton, 515, 690, 700, 763
platessa, Pleuronectes, see plaice
Platichthys stellatus, 488, 919, 1231,
1240
platypus, Paralithodes, 1039-40, 1044-
6, 1050, 1133, 1145-6
Pleurogrammus monopterygius, 480,
815,827-31
Pleuronectes platessa, see plaice
Pleuronectes quadrituberculatus, 488,
543, 1239
pleuronectids, 473, 487-9, 543, 553,
637,825, 830; see also specific
flounders
Pleurosigma spp., 778, 936
Plicifusus kroyeri, 1219-20
plovers, 726
plumchrus, Calanus, 639, 770, 826,
940, 1317
Pluvialis spp., 721-4, 727, 733, 735-6
poachers, 483-4
Podon, 951
Point Barrow, 791, 793, 828, 831
Point Dexter, 178
Point Hope, 225, 791, 828
Poland, fisheries, 1017, 1031
Polar Basin, 781
polar bears, 788-92, 794, 808
polar cod, 774, 799
polar oceanic climate region, defined,
15
polare, Buccinum, 1221
polaris acervata, Leptasterias, 1134,
1137, 1141, 1146-7, 1149-51, 1236
Polinices, 1233
pollock, see walleye pollock
pollutants, 210
polyacanthocephalus, Myoxocephalus,
1239
polyactocephalus, Chirolophis, 485, 637
polychaetes, in auklet diet, 638-9,
641 ; in cormorant diet, 641 ; distribu-
tion, 310; feeding, 769; in gray whale
diet, 829; in herring diet, 516; in
kittiwake diet, 635, 641; larvae,
774; in murre diet, 636-7, 641; in
Pacific cod diet, 1238; in plaice
diet, 1239; in puffin diet, 639-41;
in red king crab diet, 1233-4; in rock
sole diet, 1240; in sea ice, 774;
in sea star diet, 1236; in snail diet,
1224; in Tanner crab diet, 1235;
in yellowfin sole diet, 560
polynyas, 142, 145, 147, 164, 179,
186,216
polynyma, Spisula, 1151,1159,1171-3,
1176-83, 1205-13, 1234, 1236
polysaccharides, 375
Polysticta stelleri, 749
polyunsaturated acids, 376
Pomarine Jaeger, 700
pomarinus, Stercorarius, 700
Pontoporeia spp., 829, 1079, 1086
Porphyra spp., 1116
Port Clarence, fast ice, 172, 178;
flounder, 1240; herring, 514, 516,
518; ice formation, 785; ice gouging,
258, 287-9; sand ridges, 255, 258;
sediment, 310, 418; shoals, 178;
wave effects, 253, 255, 258
Port Heiden, 516-17, 814, 839-40,
1041
Port Moller, clams, 1207; harbor seal,
814; methane source, 427-30; red
king crab, 1141; salmon, 450; sea
otter, 839-40, 844; tern, 664
Port Valdez, 1235
Portlandia, 1235
Potamogeton fill for mis, 748
potassium, 324, 332
poucheti, Phaeocystis, 936, 938
predation, 612-13, 621-4, 629, 689
Preliminary Fishery Management Plan
for King and Tanner Crab, 1046
pressure, atmospheric, 90, 105-06, 109,
783
priapulids, 829
Pribilof Canyon, 8, 55
Pribilof Current, 56
Pribilof Islands, 32, 43, 54-5, 65, 135;
algae, 1116-21, 1124; amphidrome,
117; auklets, 638, 669, 706-08;
Aleutian Canada Goose, 748; Black-
bellied Plover, 727; blue king crab,
1041-2, 1048, 1050; clams, 1171-5;
Common Eider, 748; copepods, 954;
cormorants, 632, 654, 700; crab
fishery, 1040-1; fish, in seabird diet,
642; fulmars, 651, 676; Greater
Yellowlegs, 729; halibut, 497, 501,
601; herbivores, 111921, 11 24; herr-
ing, 516-17, 600, 603, 606; ice, 598,
600, 1106, 1108; Lesser Yellowlegs,
729;mollusks, 1110-15; murres, 635,
665-8, 704, 705; northern sea lion,
Pribilof Islands, cont.
861; pack ice, 1108; puffins, 639,
672-4, 708; Ruddy Turnstone, 729;
salmon, 581; sandpipers, 733-4; sea
otter, 837, 844-5; seabirds, 630, 649,
674, 677-8; seals, 449, 601, 603,
789, 814, 847-52, 870, 1242; sea-
surface temperature, 24, 26, 136;
sessile invertebrates, 1121-2; shore-
birds, 726; species density, 1111-14;
species importance, 1115; Steller sea
lion, 870; Tanner crab, 1052; tem-
perature gradients, 24; walleye pol-
lock, 478-80, 545, 600-01, 606;
walrus, 789; whale, 826, 830; winds,
137; yellowfin sole, 562, 601
pribiloffensis, Neptunea, 1219, 1221,
1224
pricklebacks, 485, 636, 816, 1231,
1240
primary production, 359, 763-73, 778-
9, 826, 831, 869, 907, 939, 948,
981, 1151, 1230, 1313-19; ben-
thic biomass relationship, 1080-1,
1083, 1087, 1097; effect on carbon
dioxide production, 347-8, 356;
hydrocarbons, 400; in ice layer, 776;
see also benthos, diatoms, ice algae,
phytoplankton
Prince of Wales Shoal, 172
Prince William Sound, 884, 1235,
1238
pristane, 384, 387, 392, 399, 402
pristene, 402
proboscidea, Limanda, 488, 553, 1028,
1029
proboscis worm, 1231
procaryotic cells, evolution, 905
Procellariformes, 679
Procellariidae, 650-1, 694
Proechinothirius fluctus, 903
profilers, 5, 34, 42
prolifera, Phyllochaetopterus, 1109
propane, concentration, 440; distribu-
tion, 91, 431-4, 436; production,
425; in sediment, 411, 413, 418-19,
422
propene, distribution, 431-4; produc-
tion, 425; in sediment, 411, 413,
418-19,422
Prorocentrum spp., 940
Protocol for Regulation of the North
Pacific Halibut Fishery, 504
protokerogen, 401
Protomedeia, 1279
Protomyctophum thompsoni. All
Protothaca staminea, 1233
Protozoa, 905
prowfish, 486
Provideniya Bukhta, 105, 109
Pseudocalanus spp., 770, 940, 942,
950-3, 984
Pseudomonas natriegens, 905
Index: St. Matthew Island 1335
psittacula, Cyclorrhynchus, 638-41,
644, 669-71, 676, 706-08, 712,
801
Pterodroma cookii, 698
Pterodroma inexpectata, 690, 698, 712
pteropods, 828
Ptilichthys goodei, 486
ptilocnemis, Calidris, 721-5, 733-4,
736
Ptychoramphus aleuticus, 638, 710-11
Puffinus spp., 631, 640, 643-4, 650,
690, 694, 696-8, 712
punctatus, Stichaeus, 485, 637
pusilla, Aethia, 638-41, 644, 670-1,
674,694, 706-08, 712
pusilla, Calidris, 721-4, 726, 732, 735
pycnocline, 213, 214, 217, 765, 767,
981
Pycnopodia helianthoides, 1234
pygmaea, Aethia, 638, 671-2, 676,
694,710-11
pygmy poacher, 483
pyrene, 404
pyrite, 910
Pyrulofusus deformis, 1223
Q
quadricornis, Hypsagonus, 483
quadricornis, Myoxocephalus, 637
quadrituberculatus, Pleuronectes, 488,
543, 1239
quillfish, 486
quinones, 404
R
radiata, Nuculana, 1232
radiation, 770-1
rainbow smelt, 476, 815
Rajidae, 829
raschii, Thysanoessa, 632-3, 635, 637,
770, 826-7
rathbuni, Asterias, 1134
rattails, 480
rayi, Neomysis, 384
rays, 830
red king crab, abundance, 1048, 1060;
diet, 1231-5; distribution, 1039-40,
1048, 1133-4, 1139-41; fishery,
1037, 1039-46, 1145-6; size, 1048-
50
Red Knot, 721-4, 731-2
Red Phalarope, 700, 721-4, 730
Red-faced Cormorant, 632, 640-1, 643-
4, 651-4, 700
Red-legged Kittiwake, 635, 640-1, 643-
4, 657, 662-3, 694, 703-04, 712
reflexa, Haloconcha, 1119-20
Reinhardtius hippoglossoides, 489, 816,
960, 1020-1, 1023, 1026-9, 1238-40
retene, 402
rex sole, 1028-9, 1232, 1235, 1240
rhamnose, 374-5
Rhinoceros Auklet, 650, 710-11
Rhizosolenia spp., 938, 941-2
Rhodostethia rosea, 700, 800, 803
ribbed sculpin, 483
ribbon seal, calving, 789, 792-3; diet,
813, 815-16, 832, 861, 1238, 1242;
food web, 818, 820; habitat, 759,
788-9, 792-3, 808, 815; hydrocar-
bons, 384
ribose, 374-5
Richardson Mountains, 297
ridibundus, Larus, 700
right-eyed flounder, 487
ringed seal, calving, 789, 792-3; diet,
813, 816, 832, 861, 1242; food web,
818, 820; habitat, 759, 788-9, 792-4,
808, 816
Rissa brevirostris, see Red-legged Kitti-
wake
Rissa tridactyla, see Black-legged Kitti-
wake
river otter, 677
river plumes, 44
river runoff, 19, 55, 68, 73, 457-8,
460
Robben Island, 850
robustus, Eschrichtius, 808, 813, 819,
825, 828-33, 1318
robustus, Hippoglossoides, 487
rockfish, 480, 827-9, 1021-3, 1029
Rock Sandpiper, 721-5, 733-4, 736
rock sole, 488, 561, 919-20, 924-8,
1028-9, 1240
rockweed, 513
ronquils, 484
rosea, Rhodostethia, 700, 800, 803
rosmarus, Odobenus, see walrus
Ross's Gull, 700, 800, 803
Ruddy Turnstone, 722-4, 726, 729-30
ruficollis, Calidris, 7 32
Rufous-necked Sandpiper, 732
Russia, see Union of Soviet Socialist
Republics
rustica macrenteron, Styela, 1143
Sabine's Gull, 701
sabini, Xema, 701
sablefish, 481-2, 960, 1020-1, 1023,
1027-9, 1239
Sadlerochit formation, 436-7
Safety Lagoon, 663, 728
saffron cod, 477, 528, 815-17, 827-
30, 1005, 1242
sagax, Sardinops, 674
Sagitta elegans, 950-1
Sagitta spp., 516
saida, Boreogadus, see arctic cod
St. George basin, 428-9, 434-5, 440,
826
St. George Island, algae, 1116-21;
auklets, 670-1; benthic biota, 1110;
current, 456; fulmars, 630, 650, 694;
herbivores, 1119-21; ice scour, 1106;
kittiwakes, 635, 662, 676, 678,
703-04; murres, 667-8, 676, 678-9,
1313; northern fur seals, 849, 852,
858; puffins 672, 708; sea otters,
844; seabirds, 674-5; sessile inverte-
brates, 1121-2; species importance,
1115-16; walleye pollock, 999; yel-
lowfin sole, 556, 561-2
St. Lawrence Island, 45; American Gol-
den Plover, 727; amphidrome, 126
auklets, 638, 641, 669-71, 675-6
690, 706-08, 801; benthic fauna
1084-5; Black-bellied Plover, 727
blue king crab, 1045; bowhead
whale, 792-3; cormorants, 653, 676
eiders, 748-9, 801; geology, 294
guillemots, 668-710; Glaucous Gull
655; goose, 745, 747; Herring Gull
701; ice, 142, 145, 147, 151, 162
164, 179, 216-17, 225, 286, 783
Lesser Yellowlegs, 729; Long-billed
Dowitcher, 731; marine birds, 713
murres, 636-7, 666-7, 705; Old-
squaw, 801; phalaropes, 730; polar
bear, 790-1; polynya, 225, 801;
puffins, 672-4; Ruddy Turnstone,
729-30; salinity, 461; salmon, 580-1;
sandpipers, 732-3; sea otter, 845;
seabirds, 649, 674-5, 677; seals,
815-16, 852; Tanner crab, 1052;
tides, 117, 123, 126-7; walleye
pollock, 527; walrus, 789, 1081;
water level, 106, 108-09; yellowfin
sole, 563; zooplankton, 947
St. Matthew basin, 296
St. Matthew Island, 145, 147, 152,
164; bivalves, 1175; Black-legged
Kittiwake, 632; blue king crab,
1041, 1045; eiders, 748, 801; flow,
67; fulmars, 650, 676-7, 694; Glau-
cous Gull, 655; halibut, 497; ice,
598, 786; marine birds, 713; murres,
705; Oldsquaw, 801; pai-ticulate
1336 Index: St. Matthew Island, cont.
St. Matthew Island, cont.
matter, 367-8; phalaropes, 730; Pi-
geon Guillemot, 668; polynyas, 216;
Ruddy Turnstone, 729-30; seabirds,
674, 677; seals, 815, 852; Slaty-
backed Gull, 801; tides, 122; walleye
pollock, 1027; walrus, 1081; Western
Sandpiper, 732; whales, 792-3, 830;
yellowfin sole, 556
St. Paul Island, cloud cover, 18; kitti-
wakes, 635, 657, 660, 662, 678;
murres, 668, 678; Northern Fulmar,
630; northern fur seal, 848-9,
852, 862-3; Red Phalarope, 730;
Ruddy Turnstone, 729; sea otter,
844-5; seabirds, 674, 904; Semi-
palmated Plover, 727; temperature,
17; Wandering Tattler, 729; yellow-
fin sole, 556, 561-2
Sakhalin Island, 581, 1238
sakhalina, Calidris alpina, 734
Salcha River, 585
salinity, 359, 460-1, 904, 976-7; effect
on fish eggs, 995, 1001, 1008;
effect on ice floes, 209; ice, 217-19,
765-7; Norton Sound, 79-84, 86-8,
90, 92; profile, 349, 362, 364-5,
368, 978; Unimak Pass, 986
salmon, abundance, 575-8, 591; des-
cription, 575, 578; diet, 589-90;
distribution, 587, 590-1; in fur seal
diet, 601; in harbor seal diet, 815;
migration, 452, 575, 578-86, 590-1,
601-03, 607-08; salinity effects, 590;
in seabird diet, 661, 675, 678;
spawning, 602; studies, 449-50, 590-
2; temperature effects, 586-9; in
walleye pollock diet, 1238; in whale
diet, 827-30; see also specific salmon
Salmonella enteriditis, 903
salmonellosis, 903
salmonids, 831
salt flux, 45, 48, 49
Samalga Island, 838-9, 852
Samalga Pass, 8
Sanak Islands, 837
sand, 307-10
sand dollar, 1231-2, 1236-40
sand fleas, 1232
sand lance, abundance, 614; in Dall
porpoise diet, 831; in halibut diet,
502, 1239; in kittiwake diet, 633-
6; larvae, 486-7; in murre diet,
636-7; in Paciflc cod diet, 1239;
in puffin diet, 639; in sea ice, 774;
in seabird diet, 642, 662; in spotted
seal diet, 815; in starry flounder
diet, 1240; in walleye pollock diet,
1238; in whale diet, 827-8
Sanderling, 722-4, 725, 732
Sandman Reef, 837
sandpipers, 721-6, 732-4
sapidus, Callinectes, 1037
sardine, see Pacific sardine
Sardinops spp., 674, 831
sarsi, Ophiura, 1086, 1232
satellite imagery, 5, 8, 70, 782; to
delineate sediment transport, 306;
to map shore, 172; to track eddies,
8; to track ice bands, 153, 197,
202; to track ice conditions, 141,
145, 147, 160, 170, 172, 178-9,
182-4, 192, 225, 264, 275, 786;
to track ice dynamics, 456; to track
ice floe migration, 151; to track ice
retreat, 162; to track melting regime,
182; to track nearshore ice, 186;
to track polynyas, 216; to track sea-
ice conditions, 1108
Savoonga, 816, 845
scalariforme, Buccinum, 1219-20, 1224
schistisagus, Larus, 700, 801
Schizoplax brandtii, 1119-20
schmidti, Bathylagus, 476
scissurata, Yoldia, 117 3
scolopaceus, Limnodromus, 721-4, 726,
731, 736
Scomber scombrus, 874
scoters, 745, 750
sculpin, 451, 483, 1016; diet, 1234-5,
1238-9; larvae, 480, 482-3; in murre
diet, 637; predators, 1239; in seal
diet, 815-18, 1239, 1242; in whale
diet, 829-30
scutulata, Littorina, 1119
scutum, Acmaea, 1120
scutum, Notoacmaea, 1119-20
sea goose, 743-5, 747
sea level, 106, 108-09, 167
sea lions, 623, 808, 830, 832, 858,
861
Sea of Okhotsk, 496, 830-1, 1080
sea otter, 807-08, 830, 837-45, 1234
sea squirts, 1233
sea stars, 1133-5, 1137, 1141-2, 1144,
1146-51, 1233-4, 1236-8, 1249
sea urchins, 1232, 1236; see also
Strongylocentrotus droebachiensis
seabirds, 774; diet, 629-43, 1313;
distribution, 689-714; effect of oil
spill, 1308-09; effect of predators,
689; food web, 1313; parasites,
904; virus, 904; see also specific
seabirds
seals, see bearded seal, harbor seal,
harp seal, hooded seal, northern fur
seal, ribbon seal, ringed seal, spotted
seal
Seal Island, 450
seal lice, 903
searchers, 484
sea-surface temperature (SST), 23-7,
133-4, 136, 164, 213-15, 599,
608, 783
Sebastes spp., 480, 1029
Sebastodes spp., 827
Sebastolobus spp., 480
secondary production, 359, 948, 950
954-60, 1238
sedge, 743, 746-7
sedimentation, 249-58, 306-10, 313-16,
335, 1269-77, 1280-6, 1290-2, 1312
sei whale, 827
Semidi Islands, 650-1, 694
Semipalmated Plover, 721-4-2, 724,
727
Semipalmated Sandpiper, 721, 726,
732,735
semipalmatus, Charadrius, 721, 727
serine, 373
Serpulidae, 907
serricata, Axinopsida, 1173
Serripes groenlandicus, 817, 1080,
1084, 1151, 1173,1236
Serripes spp., 819, 1233, 1238
sessile, Hedophyllum, 1117
sessile invertebrates, 1121-2
Seward Peninsula, 294, 728, 731-3
747-8
Shaiak Island, 675
sharks, 829-30, 858
Sharp-tailed Sandpiper, 722-4, 726, 733
shearwaters, 640, 711-13
sheefish, 514, 518
Sheep Island, 664
Shishmaref Inlet, 516-18, 1139, 1242
shoals, 178, 180-2, 218
shorebirds, 720-6, 734-6
shore ice, see fast ice
Short-billed Dowitcher, 721-4, 731, 736
Short-tailed Albatross, 694
Short-tailed Shearwater, 631, 642, 643-
4, 650, 690, 694, 696-8, 712, 1319
shrimp, 502, 632, 700, 706, 710,
814-17, 828-31, 1238, 1242; see
also pink shrimp
Siberia, 136, 726, 733, 747-8
Siberian Coastal Current, 101
Siberian high, 106, 109, 210, 225
signatus, Bathymaster, 484
silenus, Zaprora, 486
silicate, 775, 776
silicic acid, 976-8, 980, 987-8
silicon, 324, 332
Siliqua spp., 1233, 1239-41
silt, 307-10
similis, Oithona, 770
simonellite, 402
Sitkalidak Strait, 664-5
sitkana, Littorina, 1119-20
skates, 829-30
Slaty-backed Gull, 700, 801
Sledge Island, 178-9, 186, 649, 852
slender eelblenny, 485
Slender-billed Shearwater, see Short-
tailed Shearwater
Slime Bank, 449
smelts, abundance, 614; in Dall por-
poise diet, 831; distribution, 476-7;
in herring diet, 516; in Pacific cod
diet, 1238; in pinniped diet, 819;
in seabird diet, 675; in spotted seal
diet, 815; in whale diet, 827-31;
in yellowfin sole diet, 560; see
also specific smelts
Index: tumors, fish 1337
smooth lumpsucker, 484
snailfish, 484
snails, 817, 828, 1215-26, 1232, 1238
snow crab, see Tanner crab
sockeye salmon, 450, 575, 577-86,
591, 602, 605, 608, 959
Solariella sp., 1232-3
solidissima, Spisula, 1205, 1213
Somateria spp., 745, 747-9
Sooty Shearwater, 631, 643-4, 650,
694, 696-8, 712
Southeast Cape, 117, 127
Spartina, 907
spectabilis, Ophiodesoma, 907
spectabilis, Somateria, 745, 748-9
Spectacled Eider, 747, 749
sperm whale, 623, 825, 829, 832
species importance, 1114-16
spider crab, 817, 829, 1239
spinescens, Spongomorpha, 1116
spinifera, Thysanoessa, 826
spinycheek starsnout, 483
Spio filicornis, 310
Spisula polynyma, 1151, 1159, 1171-
3, 1176-7, 1179-83, 1205-13, 1234,
1236
Spisula spp., 817, 1070, 1084, 1094,
1238
sponge, 907
Spongomorpha, 1116, 1118
spotted seals, calving, 789, 792-3;
diet, 813, 815, 832, 861, 1242,
1318; distribution, 759, 788-9, 792-
3, 808, 815, 873; energy require-
ment, 891; food web, 818, 820;
growth rate, 883-4; heavy metal
content, 342; hydrocarbons, 384;
metabolism, 887-8
Squaliformes, 829
squatarola, Pluvialis, 721-4, 727
squid, 631, 635, 637, 694, 696, 826-7,
829-32, 857-8, 1033
Stadukhin, 807
staminea, Protothaca, 1233
stamukhi, 168-70, 265, 275
starry flounder, 488, 919, 1028-9,
1231, 1240
stejnegeri, Mesoplodon, 825, 830
Stejneger's beaked whale, 825, 830
Stellersea cow, 807, 809
Steller sea lion, 655, 666, 813, 818; see
also sea lions
Steller's Eider, 749
stellatus, Platichthys, 488, 919,1028-9,
1231, 1240
telleri, Polysticta,, 749
Stenobrachius leucopsarus. All
Stenodus leucichthys, 514, 518
stenolepis, Hippoglossus, see Pacific
halibut
steranes, 402
Stercorarius spp., 700
Sterna spp., 663-5, 704
Stichaeidae, 485-6, 636
Stichaeus punctatus, 485,637
stomias, Atheresthes, 487, 1232
storm-petrels, 651, 679, 690
storm surge, 258
storms, 15, 19-20, 251-3, 258
stout blacksmelt, 476
stout eelblenny, 485
striatula, Fragilaria, 778, 936
Strongylocentrotus spp., 1076, 1124,
1232-3, 1236
Stuart Island, 88-9, 91-2, 178, 275
sturgeon poacher, 483
Styela rustica macrenteron, 1143
subruficollis, Tryngites, 734
sulcata, Melosira, 111
sulfur analysis, 390
Surf Scoter, 7 50
Surfbird,731
suspended particulate matter, 321-2,
325-9
Sverdrup waves, 126
Synthliboramphus antiquus, 710-11
tadpole snailfish, 484
taeniata, Achnanthes, 778
taenia ta, Alaria, 1117
tahitiensis, Numenius, 728-9
Taiwan, fisheries, 542, 1017, 1023
Tanner crab, 451; abundance, 1060-1;
in bearded seal diet, 817; diet, 1155,
1175-6, 1231; distribution 1052-
3, 1133, 1141-4; fishery, 1037-
40, 1047, 1051, 1053-61, 1131,
1144-5; food web, 1231, 1234; in
halibut diet, 503, 1239; predators,
1235; in sculpin diet, 1239; in sperm
whale diet, 829; in walleye pollock
diet, 1238; in walrus diet, 817
tanneri, Chionoecetes, 1051
taverneri, Branta canadensis, 745-6
Taverner's Canada Goose, 745-6
tectonic evolution, Bering Strait, 293,
297-9
Teleostei, 950
Tellina
Teleostei, 950
Tellina lutea, 1151, 1159, 1165, 1167-
8, 1173-83, 1236, 1240
Tellina spp., 1094, 1233
temperature, air, 598-604; bottom, 461,
466-8, 598-606, 1220; cycle, 566;
effect on marine organisms, 995-7,
999-1001, 1110, 1151, 1220; gra-
dients, 24, 79-84, 86-8, 90, 92;
profile, 359, 362-5, 368; regime,
456-63, 465-7, 598-604; related to
fish abundance, 450; sea-surface,
23-7, 133-4, 136, 164, 213-15,
599, 608, 783; variations, 16-17,
995-7 ; water, 976-7, 986, 997
temulens, Cylindropyxis, 940
Tenilny Range, 293
tenuirostris, Puffinus, 631, 640, 644,
650, 690, 694, 696-8, 712
tenuis, Nucula, 1159-61, 1165, 1173-
83, 1231, 1235
Thalassiophyllum spp., 1124
Thalassiosira spp., 778, 936, 938,
940-1
thayeri, Larus, 700
Thayers Gull, 700
Themisto spp., 516
Theragra chalcogramma, see walleye
pollock
thermocline, 765, 767, 936, 976, 978-9
theta, Diaphus, All
Thick-billed Murre, 665, 667-8, 671,
677; diet, 636-7, 640-1, 644, 1319;
distribution, 667, 694, 704-06;
hydrocarbons, 384
Thioploca, 905
thompsoni, Protomyctophum, All
Thyasira flexuosa, 1173
Thysanoessa spp., 541, 632-3, 635,
637, 639, 770, 826-7, 950-1, 959,
1238
tiarella, Pennaria, 907
tides, 170-1, 217, 463-5; crack, 167,
170; currents, 45-6, 49, 56, 58-9,
62-5, 68, 70-2, 84, 113, 117, 122-6,
224; diurnal, 113-14, 117, 119,
122-3; eddies, 689; effect on fast
ice, 167, 170; semidiurnal, 112-14,
117, 119, 122-3; study of, 12, 111-
12, 117-22
Tigalda Island, 838-9
Tintina fault, 298
Tipulidae, 726
Tokiak,600
Togiak Bay, 581-2, 1174
Togiak River, 1156
toothed whales, 825, 826; see also
specific whales
Tortanus discaudatus, 947, 951
Toxadocia violacea, 907
Transverse Current, 464; see also
Bering Slope Current
Travisia forbesii, 1240
Trematomus borchgrevinki, 11 A
Trichodon trichodon, 1239
tridactyla, Rissa, see Black-legged Kitti-
wake
Triglops pingeli, ASS, 636
Triglops spp., 483
Tringa spp., 729
trispinosa, Odontopyxis, 483
triterpanes, 392, 402-04
troschelii, Evasterias, 1234
truncata. My a, 817
Tryngites subruficollis, ISA
tshawytscha, Oncorhynchus, 575, 577-
80, 582-3,585-6, 591
Tufted Puffin, 639-41, 644, 673-7
694,708-09, 712
tumors, fish, 919-22, 927-8
1338 Index: tunicata, Katharina
tunicata, Katharina, 1119
tunicates, 817,907,1143
turbellarians, 774
turbot, 473
turnstones, 726; see also Ruddy Turn-
stone, Black Turnstone
Twin Island, 675
u
Ugashik Bay, 746-7, 839, 1097, 1207
Ugashik River, 44
Ulca bolini, 542
Ulva spp.„ 1116, 1119
Umnak Island, 838
Unalakleet, 310
Unalaska Bay, 708
Unalaska Island, 839, 852
Unimak Island, clams, 1172; herring,
603, 606; red king crab fishery,
1041; salinity, 461; sea otter, 837,
839; Tanner crab, 1141; walleye
pollock, 480, 600, 606, 999, 1001;
yellowfin sole, 556, 561-2
Unimak Pass, albatross, 694, ammonium
distribution, 986-7; copepods, 954;
currents, 305; ethane source, 434-5;
ethene source, 434; halibut, 497,
501; herring, 517; ichthyoplankton,
475-90; methane source, 428, 430-1;
nitrate distribution, 986-7; northern
fur seal, 852, 861; northern sea lion,
861 ; sea otter, 838; walleye pollock,
478-80, 1006
Union of Soviet Socialist Republics,
crab fishery, 1040, 1045-7, 1054-
8; fisheries, 542, 554-5, 557, 1017,
1021-3, 1025, 1029; fishery agree-
ments, 1031, 1040
United States Bureau of Fisheries, 807
United States Fishery Conservation and
Management Act, 448, 496, 542,
870, 1015, 1026, 1030, 1032; see
also Magnuson Fishery Conservation
and Management Act
United States National Marine Fisheries
Service (NMFS), 1215
United States Public Law 88-308, 1030
United States Public Law 89-658, 1030
United States Public Law 94-265, 542
upwelling, 8, 48, 347, 359, 371, 690,
701
urea, 373
Uria aalge, see Common Murre
Uria lomvia, see Thick-billed Murre
uriae, Ixodes, 904
urile, Phalacrocorax, 632, 640-1,651-4,
700
Urochordata, 1137
ursinus, Callorhinus, 601, 607, 623,
808, 818, 847-63, 873, 1313
Ursus maritimus, 788-92, 794, 808
valine, 373
vanadium, 314
vegae, Larus argentatus, 650, 654, 701
Venericardia, 1232
ventricosa, Neptunea, 1219-20, 1223-4
ventricosus, Aptocyclus, 484
verrucosa, Montipora, 907
Vibrio spp., 904
villosus, Mallotus, 631, 633, 635-7,661
violacea, Toxadocia, 907
virgata, Aphriza, 731
viruses, 904
vitamins, 908-09
vitulina, Phoca, see harbor seal
vitulina largha, Phoca, see spotted seal
Volutopsius fragilis, 1219-21
Vsevidof Island, 839
w
Wales, 172, 186, 225, 723, 816; see
also Prince of Wales Shoal
walleye pollock, 7, 630; abundance,
449-51, 530-1, 554, 614; in arrow-
tooth flounder diet, 542; in auklet
diet, 542, 634, 639; in avifauna
diet, 527; in cormorant diet, 542,
632, 644; in cottid diet, 542; des-
cription, 533-7, 544-6; diet, 1232,
1235, 1238, 1313; distribution,
478-80, 527-30, 540, 770, 960,
1034; eggs, 478-80, 606, 993,
995, 997-1008; fishery, 527, 542-4,
1019-21, 1023, 1025-9; food web,
10, 540-2, 1231, 1235, 1313; in
fulmar diet, 630, 644, 676-7, 694; in
haUbut diet, 502, 542, 1239; in
harbor seal diet, 869-70; in herring
diet, 516; in jaeger diet, 700; in
kittiwake diet, 542, 632-5, 644;
larvae, 478-80, 606, 954, 993,
1006, 1008; life cycle, 348; migra-
tion, 452, 598-606, 608, 1007;
in murre diet, 542, 635-7, 644,
1319; neuston, 1006; in Pacific cod
diet, 1238; predators, 1238; in puffin
diet, 542, 639, 644; in sablefish diet,
542; in sculpin diet, 1239; in seabird
diet, 642, 661, 677-8, 802;spawning,
473, 475, 537-8, 598-601, 604, 606-
07, 993, 1001, 1005-07; in spotted
seal diet, 869-70; in Steller sea lion
diet, 542, 870; in whale diet, 527,
542,827, 831-2
walrus, 813-22, 1317-18; calving, 790,
793; diet, 813, 817, 1235, 1237,
1241, 1248-9, 1313; food web,
818, 1313; habitat, 759, 788-90,
walrus, cont.
792-3, 808, 817; as prey of killer
whale, 830
Walrus Island, 655, 666, 674-5
Walrus Islands, 652, 705
Walvis Bay, 400
Wandering Tattler, 729
water-level anomaly, 106, 108-09
water transport, 95-110
wave effects, 253
West Alaska Current, 56
Western Gull, 641, 700
Western Sandpiper, 722-6, 732, 736
whale, 819, 826, 1316, 1318; see also
specific whales
whelk, 1134, 1137-9, 1151
Whimbrel, 726, 728
Whiskered Auklet, 638, 671-2, 676,
694, 710-11
Whistling Swan, 745-6
White Sea, 1080
white whale, see beluga whale
whitefish, 830
White-fronted Goose, 745-7
White-winged Scoter, 750
whiting, 831
wildUfe management, 807, 809
wildlife preservation, 11
winds, effect on ice floes, 151-3, 155,
164, 203-04, 207, 210; offshore,
216; sea-surface temperature rela-
tionship, 27; stress, 189; surface,
18-19, 84, 107, 110, 133, 136-7,
142,162, 164,172
winter halibut savings area, 1030
Wood River, 590
Wrangel Arch, 294, 297, 299-300
Wrangel Island, 294-6, 299, 745, 747
wrymouth, 486
Xema sabini, 701
xylose, 374-5
Yanuska Island, 650
yellowfin sole, 553-69; abundance, 449,
51, 542, 553-5, 569; description,
557-60; diet, 560-1, 1176, 1232,
1241; distribution, 553, 555-7, 560-
2, 567-9, 960, 1028; fishery, 554,
558, 1019-23, 1025-6, 1028; food
web, 1231, 1237; in halibut diet.
Index: Zostera spp. 1339
yellowfin sole, cont.
502, 560, 606, 1239, 1241; larvae,
488; migration, 452, 562, 567-9,
598-605; spawning, 473, 475, 563,
569, 602, 607-08
Yoldia amygdalea, 1159, 1165-7, 1169-
70, 1173-4, 1176-7, 1179-80, 1182
Yoldia hyperborea, 1231, 1239, 1240
Yoldia jo hanni, 1239
Yoldia scissurata, 1165, 1173
Yoldia spp., 1232-3, 1235, 1238, 1241
Yukon Delta, 179, 723; Bar-tailed God-
wit, 728; Black-bellied Plover, 727;
Black Brant, 744, 747; Black Scoter,
750; Black Turnstone, 730; Bristle-
thighed Curlew, 728-9; Common
Snipe, 731; description, 279, 743;
Dunlin, 723, 726, 734; eiders, 744-
5, 748-9; geese, 739-40, 744-7;
Greater Scaup, 748; Greater Yellow-
legs, 729; harbor seal, 873; ice goug-
ing, 286; ice movement, 282; Long-
billed Dowitcher, 728, 731; methane
source, 418, 422; morphology, 265
Oldsquaw, 745, 749-50; peaty sed
iment, 418, 422; phalaropes, 730
Pintail, 744, 745; Red Knot, 723
731; Ruddy Turnstone, 726, 729
Sanderling, 732; sandpipers, 723
726, 732-4; sedimentary processes
24953, 264, 269; shorebirds, 721
723, 726; Surf Scoter, 750; tides
Yukon Delta, cont.
127; Wandering Tattler, 729; water-
fowl, 739, 750; Western Sandpiper,
723; Whimbrel, 728; Whistling Swan,
745-6; White-winged Scoter, 750
Yukon-Koyukuk basin, 294, 296-7
Yukon-Kuskokwim Delta, 830
Yukon River, 91-2, 178, 180, 1080
discharge, 249, 456; as source of
fresh water, 19, 90, 460, 675
herring, 511, 516; king salmon
607-08; Lesser Snow Goose, 747
methane source, 429; Pintail, 748
plume, 82, 325-8; salinity, 82
salmon, 581, 586; sediment source
310, 313, 316, 323, 325, 328, 1312
source of suspended particulates,
323, 325-8; Taverner's Canada
Goose, 746; terrestrial detritus,
1151; White-fronted Goose, 746
Yukon River prodelta, 178, 179,
279-88
zachirus, Glyptocephalus, 1232
Zaimaka Island, 656
Zapadni Bay, 1108
Zaprora silenus, 486
Zaproridae, 486
Zhemchug Canyon, 608, 980
zinc, 321, 324, 332-5, 342
Ziphius cauirostris, 825, 830
Zoarcidae, 480
zonifer, Erilepis, 481
zooplankton, 759; in auklet diet,
638; in baleen whale diet, 826;
in bird diet, 712; in Black-legged
Kittiwake diet, 701; carbon isotopic
value, 401; consumption of, 622,
826; distribution, 947-54, 988; effect
of oil spill, 1305, 1308; in fish
diet, 452; food web, 1313; grazing,
981; in herring diet, 510, 515-16,
518; ingestion, 940, 1313; produc-
tion, 954-60, 1317; in puffin diet,
708; in salmon diet, 589; in seabird
diet, 674-5, 799, 802; in storm-
petrel diet, 651; in walleye pollock
diet, 527; in yellowfin sole diet,
560
Zostera marina, 389, 401, 404, 513, 743,
747,799, 1097, 1137
Zostera spp., 513
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